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C# Console Calculator with all input on a one line

I am trying to make a program that is a small console calculator where the input is inserted on a single line in the console. example the input "88+12*7/2" should be translated into a math operation looking like this => "((88+ 12) * 7)/2" and print answer in the console.
I will be grateful if you help me to complete this code...
I did a part of the project but it only works to do the operator on two numbers
static string Input_User()
{
string Input_User = Console.ReadLine();
return Input_User;
}
static void ShowMessage()
{
Console.WriteLine("Enter your numbers with operation like: 7*7");
}
ShowMessage();
string input_string = Input_User();
int result = PerformCalculation(InputToList(input_string));
Console.WriteLine($"{input_string}={result}");
static string[] InputToList(string input)
{
string number1 = "";
string number2 = "";
string Oprt = "";
string[] Arithmetic = new string[3];
int n = 0;
foreach (char charecter in input)
{
int num;
bool isNumerical = int.TryParse(charecter.ToString(), out num);
n += 1;
if (isNumerical)
{
number1 += num;
}
else
{
Oprt = charecter.ToString();
Arithmetic[0] = number1;
Arithmetic[1] = Oprt;
for (int i = n; i <= input.Length - 1; i++)
{
number2 += input[i];
}
Arithmetic[2] = number2;
}
}
return Arithmetic;
}
static int PerformCalculation(string[] Input)
{
int result = 0;
switch (Input[1])
{
case "+":
result = Int32.Parse(Input[0]) + Int32.Parse(Input[2]);
break;
case "-":
result = Int32.Parse(Input[0]) - Int32.Parse(Input[2]);
break;
case "*":
result = Int32.Parse(Input[0]) * Int32.Parse(Input[2]);
break;
case "/":
result = Int32.Parse(Input[0]) / Int32.Parse(Input[2]);
break;
}
return result;
}

If your input would be for example '5 + 5 + 5' it would not work because your function InputToList would do the following
InputToList("5+5+5")
-> Return Value ["5","+","5+5"]
The function PerformCalculation would now try to parse 5+5 to an Integer, and that's simply not possible.
One Solution would be to use regular expressions to filter and check the input.
Then you could use a binary tree or a linked list in which you insert the numbers and operators.
After this you would be able to iterate over the list/tree and to do multiple operations.

How can I use ParameterExpression to parameterize an expression tree?

I am learning to use expression trees/expressions in C#. I have gradually built up a parser, with which I can take a string in "calculator" syntax (like "2 * 3 + 14 * 4 / 7 - 5 * 5") and build and evaluate an abstract syntax tree (AST). It even calculates the correct answer! :-) The AST consists of Expression nodes: arithmethical binary nodes (Add, Subtract, Multiply, Divide) and unary Constant nodes representing the integer values.
Next step: I want to add parameters to the expression to be parsed, like "2 * 3 + myVar1 * 4 / 7 - 5 * myVar2", and supply the actual values for the parameters at runtime (after the AST has been compiled). I can easily add the ParameterExpressions to the tree - but I cannot find out how to correctly compile my tree and supply the values.
The parser is built using Coco/R and an attributed Bachus-Naur grammar, and looks like this:
using System.Linq.Expressions;
using Ex = System.Linq.Expressions.Expression;
using System;
namespace AtgKalk
{
public class Parser
{
public const int _EOF = 0;
public const int _identifikator = 1;
public const int _tall = 2;
public const int _pluss = 3;
public const int _minus = 4;
public const int _ganger = 5;
public const int _deler = 6;
public const int maxT = 7;
const bool T = true;
const bool x = false;
const int minErrDist = 2;
public Scanner scanner;
public Errors errors;
public Token t; // last recognized token
public Token la; // lookahead token
int errDist = minErrDist;
public Parser(Scanner scanner)
{
this.scanner = scanner;
errors = new Errors();
}
void SynErr(int n)
{
if (errDist >= minErrDist) errors.SynErr(la.line, la.col, n);
errDist = 0;
}
void Get()
{
for (; ; )
{
t = la;
la = scanner.Scan();
if (la.kind <= maxT) { ++errDist; break; }
la = t;
}
}
void Expect(int n)
{
if (la.kind == n) Get(); else { SynErr(n); }
}
void Calculator()
{
Ex n;
CalcExpr(out n);
Console.Write($"AST: {n} = ");
Console.WriteLine(Ex.Lambda<Func<int>>(n).Compile()());
// The above works fine as long as there are no parameter names in the input string
}
void CalcExpr(out Ex n1)
{
Ex n2; Func<Ex, Ex, Ex> f;
Term(out n1);
while (la.kind == 3 || la.kind == 4)
{
AddOp(out f);
Term(out n2);
n1 = f(n1, n2);
}
}
void Term(out Ex n1)
{
n1 = null; Ex n2; Func<Ex, Ex, Ex> f = null;
Fact(out n1);
while (la.kind == 5 || la.kind == 6)
{
MulOp(out f);
Fact(out n2);
n1 = f(n1, n2);
}
}
void AddOp(out Func<Ex, Ex, Ex> f)
{
f = null;
if (la.kind == 3)
{
Get();
f = (l, r) => Ex.Add(l, r);
}
else if (la.kind == 4)
{
Get();
f = (l, r) => Ex.Subtract(l, r);
}
else SynErr(8);
}
void Fact(out Ex n)
{
n = null;
if (la.kind == 2)
{
Number(out n);
}
else if (la.kind == 1)
{
Parameter(out n);
}
else SynErr(9);
}
void MulOp(out Func<Ex, Ex, Ex> f)
{
f = null;
if (la.kind == 5)
{
Get();
f = (l, r) => Ex.Multiply(l, r);
}
else if (la.kind == 6)
{
Get();
f = (l, r) => Ex.Divide(l, r);
}
else SynErr(10);
}
void Number(out Ex n)
{
Expect(2);
n = Ex.Constant(int.Parse(t.val), typeof(int));
}
void Parameter(out Ex n)
{
Expect(1);
n = Ex.Parameter(typeof(int), t.val);
}
public void Parse()
{
la = new Token();
la.val = "";
Get();
Calculator();
Expect(0);
}
static readonly bool[,] set = {
{T,x,x,x, x,x,x,x, x}
};
} // end Parser
public class Errors
{
public int count = 0; // number of errors detected
public System.IO.TextWriter errorStream = Console.Out; // error messages go to this stream
public string errMsgFormat = "-- line {0} col {1}: {2}"; // 0=line, 1=column, 2=text
public virtual void SynErr(int line, int col, int n)
{
string s;
switch (n)
{
case 0: s = "EOF expected"; break;
case 1: s = "identifikator expected"; break;
case 2: s = "tall expected"; break;
case 3: s = "pluss expected"; break;
case 4: s = "minus expected"; break;
case 5: s = "ganger expected"; break;
case 6: s = "deler expected"; break;
case 7: s = "??? expected"; break;
case 8: s = "invalid AddOp"; break;
case 9: s = "invalid Fakt"; break;
case 10: s = "invalid MulOp"; break;
default: s = "error " + n; break;
}
errorStream.WriteLine(errMsgFormat, line, col, s);
count++;
}
} // Errors
public class FatalError : Exception
{
public FatalError(string m) : base(m) { }
}
}
My problem lies in line 63, I think:
Console.WriteLine(Ex.Lambda<Func<int>>(n).Compile()());
Invocation:
Scanner scanner = new Scanner(args[0]); // if args[0] contains the input string :-)
Parser parser = new Parser(scanner);
parser.Parse();

I have now solved my problem. Thanks to kaby76 for valuable tips leading me in the right direction. The example now can handle an arbitrary number of parameters (probably max 16, since this is the maximum number of input arguments for Func<...>)
The solution to the problem war threefold:
Collect the parameters and supply this collection of parameters to the Lambda
Remove the explicit type arguments from the Lambda, letting it infer types
Use DynamicInvoke to execute the resulting Delegate
The problematic statement then looks like this, for an expression with two parameters:
Console.WriteLine(Ex.Lambda(n, para).Compile().DynamicInvoke(3, 4));

can i recover the source of my compiled application?

I just lost my library and i have a lot of lines of unnecesary code once time i decompile it. It's possible recover or understand more or less the code to rewrite completely to the original source?
For example if i check one part of my projects, i can put one example of how will be the original source before try to decompile it:
private static bool ByteArrayCompare(byte[] b1, byte[] b2)
{
return b1.Length == b2.Length && memcmp(b1, b2, b1.Length) == 0;
}
Once time i decompile it, the code is completely different:
private static bool ByteArrayCompare(byte[] b1, byte[] b2)
{
if (b1.Length == b2.Length)
{
while (true)
{
int num = 719326676;
goto IL_000d;
IL_000d:
uint num2;
switch ((num2 = (uint)(num ^ 0x6B86E2FE)) % 3u)
{
case 0u:
break;
case 1u:
return SMPTR.memcmp(b1, b2, b1.Length) == 0;
default:
goto IL_0048;
}
continue;
IL_0039:
num = ((int)num2 * -1900091540 ^ 0x4DAC5FA);
goto IL_000d;
}
}
goto IL_0048;
IL_0048:
return false;
}
Now happen the same with these classes.
Run:
public static bool Run()
{
header.‫‬‭‪‪​‎‍‬‌‫‎‫‏‫‭‍‪‮‍‌​​‬‌​header.‪‫‏‎‮‬‎‬​‮‮‪‏‭‎‪‮‭​‏‌​‭‫​‭‮(), header.CurrentDomain_AssemblyResolve);
while (true)
{
int num = 1039260164;
goto IL_001b;
IL_001b:
uint num2;
while (true)
{
int num3 = default(int);
switch ((num2 = (uint)(num ^ 0x3472CD9D)) % 8u)
{
case 0u:
break;
case 3u:
return true;
case 4u:
num = ((int)num2 * -188976845 ^ -260518362);
continue;
case 7u:
goto IL_006c;
case 6u:
goto IL_0081;
case 1u:
num3 = 1;
num = ((int)num2 * -1593869856 ^ 0x44175289);
continue;
case 2u:
num3++;
num = 179700154;
continue;
default:
return false;
}
break;
IL_0081:
int num4;
if (!RunHandler.HandleRun())
{
num = 311890711;
num4 = num;
}
else
{
num = 483767846;
num4 = num;
}
continue;
IL_006c:
int num5;
if (num3 > 5)
{
num = 822334488;
num5 = num;
}
else
{
num = 1601113283;
num5 = num;
}
}
continue;
IL_004e:
num = ((int)num2 * -75964955 ^ 0x5EDD0E50);
goto IL_001b;
}
}
And the second class:
private static Assembly CurrentDomain_AssemblyResolve(object sender, ResolveEventArgs args)
{
if (header.id != null)
{
goto IL_0007;
}
goto IL_003e;
IL_003e:
header.id = header.​‏‍‍‏‎‪‫‪‬‏‬‫​‫‪‌‌‌‪‭​‫​‮‏‭‫‮(args);
int num = -782795078;
goto IL_000c;
IL_000c:
uint num2;
switch ((num2 = (uint)(num ^ -504079301)) % 4u)
{
case 0u:
break;
case 2u:
return null;
case 3u:
goto IL_003e;
default:
return header.‮​‬‭‮‪‬‫‌‌‬‫​‍‍‮‬‬‮‭‪‮(Resources.MyDLL;
}
goto IL_0007;
IL_0007:
num = -1157763175;
goto IL_000c;
IL_002f:
num = ((int)num2 * -823262644 ^ -680184524);
goto IL_000c;
}
It's possible to recover the code of the last two classes. why the code compiled add a lot of loops and make very hard to understand what really happen? It's possible to recover it?

Marshal a va_list

I have the following code:
[UnmanagedFunctionPointer(CallingConvention.Cdecl)]
public delegate void PanicFuncDelegate(string str, IntPtr args);
private void PanicFunc(string str, IntPtr args)
{
LogFunc("PANIC", str, args);
}
public void LogFunc(string severity, string str, IntPtr args)
{
vprintf($"[{severity}] "+ str,args);
}
[DllImport("libc.so.6")]
private static extern int vprintf(string format, IntPtr args);
This prints to the console the messages correctly formatted. I want to retrieve the values from args to use them in my own logger.
If I try to get the value of each pointer from the array in args (as suggested here: Marshal va_list in C# delegate) I get segmentation fault.
Any suggestions?

I have a function call with this working, here's what I do:
For the DLLImport I use an __arglist to marshall to the va_list,
[DllImport("libc.so.6")]
private static extern int vprintf(string format, __arglist);
Then when calling the function I create the __arglist,
vprintf(string format, __arglist(arg1, arg2, arg3...))
Ofcourse you would need to either call the function with all the arguments statically or build that __arglist dynamically, I don't have the code here but it's possible.
I wonder if you get a segmentation fault because the elements in the object[] are not pinned? Maybe if you pin the object[] and all elements within that would help? Just a guess though.

Just think on how C program gets variables from va_list, and there is the solution:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Runtime.InteropServices;
using System.Text;
namespace VaTest
{
class Program
{
static void Main(string[] args)
{
MarshalVaArgs(vaList => vprintf("%c%d%s", vaList), false, 'a', 123, "bc");
}
[DllImport("msvcrt")] //windows
//[DllImport("c")] //linux
private static extern int vprintf(string format, IntPtr vaList);
private static int IntSizeOf(Type t)
{
return (Marshal.SizeOf(t) + IntPtr.Size - 1) & ~(IntPtr.Size - 1);
}
public static void MarshalVaArgs(Action<IntPtr> action, bool? isUnicode, params object[] args)
{
var sizes = new int[args.Length];
for (var i = 0; i < args.Length; i++)
{
sizes[i] = args[i] is string ? IntPtr.Size : IntSizeOf(args[i].GetType());
}
var allocs = new List<IntPtr>();
var offset = 0;
var result = Marshal.AllocHGlobal(sizes.Sum());
allocs.Add(result);
for (var i = 0; i < args.Length; i++)
{
if (args[i] is string)
{
var s = (string)args[i];
var data = default(IntPtr);
if (isUnicode.HasValue)
{
if (isUnicode.Value)
{
data = Marshal.StringToHGlobalUni(s);
}
else
{
data = Marshal.StringToHGlobalAnsi(s);
}
}
else
{
data = Marshal.StringToHGlobalAuto(s);
}
allocs.Add(data);
Marshal.WriteIntPtr(result, offset, data);
offset += sizes[i];
}
else
{
Marshal.StructureToPtr(args[i], result + offset, false);
offset += sizes[i];
}
}
action(result);
foreach (var ptr in allocs)
{
Marshal.FreeHGlobal(ptr);
}
}
}
}
The code is written and tested with .NET Core 3.0 preview 5, compatible with .NET Framework 4.0 and C# 3.0.
Outputs:
a123bc

As this isn't solved yet i post a long solution that worked for me.
I found the solution in an abandoned project
https://github.com/GoaLitiuM/libobs-sharp
Use like this (tested with FFmpeg):
var objects = va_list_Helper.VaListToArray(format, va_List_Ptr);
// format: frame=%4d QP=%.2f NAL=%d Slice:%c Poc:%-3d I:%-4d P:%-4d SKIP:%-4d size=%d bytes%s
// format (filled): frame= 3 QP=13.00 NAL=0 Slice:B Poc:4 I:0 P:8 SKIP:912 size=32 bytes
// va_List objects: 3, 13, 0, 'B', 4, 0, 8, 912, 32
The classes needed:
public class va_list_Helper
{
public static unsafe object[] VaListToArray(string format, byte* va_list)
{
var vaList = new va_list((IntPtr)va_list);
return vaList.GetObjectsByFormat(format);
}
}
public static class Printf
{
// used
public static string[] GetFormatSpecifiers(string format)
{
if (format.IndexOf('%') == -1)
return null;
// find specifiers from format string
List<int> indices = new List<int>();
for (int j = 0; j < format.Length; j++)
{
j = format.IndexOf('%', j);
if (j == -1)
break;
indices.Add(j);
if (format[j + 1] == '%') // ignore "%%"
j++;
}
if (indices.Count == 0)
return null;
List<string> formats = new List<string>(indices.Count);
for (int mi = 0; mi < indices.Count; mi++)
{
string formatSpecifier = format.Substring(indices[mi], (mi + 1 < indices.Count ? indices[mi + 1] : format.Length) - indices[mi]);
if (!string.IsNullOrWhiteSpace(formatSpecifier))
formats.Add(formatSpecifier);
}
return formats.ToArray();
}
public class FormatSpecificationInfo
{
public string specification;
//public int parameter;
public char type;
public int width;
public int precision;
public FormatFlags flags;
};
[Flags]
public enum FormatFlags
{
// Type length
IsLong = 0x0001, // l
IsLongLong = 0x0002, // ll
IsShort = 0x0004, // h
IsChar = 0x0008, // hh
IsLongDouble = 0x0016, // L
// Flags
LeftAlign = 0x0100, // '-' left align within the width
Sign = 0x0200, // '+' use - or + signs for signed types
Alternate = 0x0400, // '#' prefix non-zero values with hex types
ZeroPad = 0x0800, // '0' pad with zeros
Blank = 0x1000, // ' ' pad sign with blank
Grouping = 0x2000, // '\' group by thousands
ArchSize = 0x4000, // '?' use arch precision
// Dynamic parameters
DynamicWidth = 0x10000,
DynamicPrecision = 0x20000,
};
// used
public static FormatSpecificationInfo GetFormatSpecifierInfo(string specification)
{
if (string.IsNullOrWhiteSpace(specification))
return null;
FormatSpecificationInfo info = new FormatSpecificationInfo()
{
type = '\0',
width = int.MinValue,
precision = 6,
};
string width = "";
string precision = "";
int start = -1;
int fsLength = 1;
// TODO: parse parameter index
for (int i = 0; i < specification.Length && info.type == '\0'; i++)
{
char c = specification[i];
switch (c)
{
case '%':
if (start == -1)
start = i;
else
info.type = c;
info.specification = specification.Substring(start, i + 1 - start);
fsLength = i + 1;
break;
// flags
case '-':
info.flags |= FormatFlags.LeftAlign;
break;
case '+':
info.flags |= FormatFlags.Sign;
break;
case ' ':
info.flags |= FormatFlags.Blank;
break;
case '#':
info.flags |= FormatFlags.Alternate;
break;
case '\'':
info.flags |= FormatFlags.Grouping;
break;
case '?':
info.flags |= FormatFlags.ArchSize;
break;
// precision
case '.':
{
for (int j = i + 1; j < specification.Length; j++)
{
if (specification[j] == '*')
info.flags |= FormatFlags.DynamicPrecision;
else if (char.IsNumber(specification[j]))
precision += specification[j];
else
break;
i++;
}
}
break;
// length flags
case 'h':
info.flags += (int)FormatFlags.IsShort;
break;
case 'l':
info.flags += (int)FormatFlags.IsLong;
break;
case 'L':
info.flags |= FormatFlags.IsLongDouble;
break;
case 'z':
case 'j':
case 't':
// not supported
break;
// dynamic width
case '*':
info.flags |= FormatFlags.DynamicWidth;
break;
default:
{
if (char.IsNumber(c))
{
if (width == "" && c == '0')
info.flags |= FormatFlags.ZeroPad;
else
width += c;
}
else if (char.IsLetter(c) && info.type == '\0')
{
info.type = c;
info.specification = specification.Substring(start, i + 1 - start);
fsLength = i + 1;
}
}
break;
}
}
// sign overrides space
if (info.flags.HasFlag(FormatFlags.Sign) && info.flags.HasFlag(FormatFlags.Blank))
info.flags &= ~FormatFlags.Blank;
if (info.flags.HasFlag(FormatFlags.LeftAlign) && info.flags.HasFlag(FormatFlags.ZeroPad))
info.flags &= ~FormatFlags.ZeroPad;
// unsupported precision for these types
if (info.type == 's' ||
info.type == 'c' ||
Char.ToUpper(info.type) == 'X' ||
info.type == 'o')
{
info.precision = int.MinValue;
}
if (!string.IsNullOrWhiteSpace(precision))
info.precision = Convert.ToInt32(precision);
if (!string.IsNullOrWhiteSpace(width))
info.width = Convert.ToInt32(width);
return info;
}
}
public class va_list
{
internal IntPtr instance; //unmanaged pointer to va_list
public va_list(IntPtr ptr)
{
instance = ptr;
}
/// <summary> Returns unmanaged pointer to argument list. </summary>
public IntPtr GetPointer()
{
return instance;
}
/// <summary> Returns array of objects with help of printf format string. </summary>
/// <param name="format"> printf format string. </param>
public object[] GetObjectsByFormat(string format)
{
return GetObjectsByFormat(format, this);
}
public static unsafe object[] GetObjectsByFormat(string format, va_list va_list)
{
string[] formatSpecifiers = Printf.GetFormatSpecifiers(format);
if (formatSpecifiers == null || va_list == null || va_list.GetPointer() == IntPtr.Zero)
return null;
IntPtr args = va_list.GetPointer();
List<object> objects = new List<object>(formatSpecifiers.Length);
//var bytesDebug = new byte[format.Length];
//Marshal.Copy(va_list.GetPointer(), bytesDebug, 0, bytesDebug.Length);
int offset = 0;
foreach (string spec in formatSpecifiers)
{
var info = Printf.GetFormatSpecifierInfo(spec);
if (info.type == '\0')
continue;
// dynamic width and precision arguments
// these are stored in stack before the actual value
if (info.flags.HasFlag(Printf.FormatFlags.DynamicWidth))
{
int widthArg = Marshal.ReadInt32(args, offset);
objects.Add(widthArg);
offset += Marshal.SizeOf(typeof(IntPtr));
}
if (info.flags.HasFlag(Printf.FormatFlags.DynamicPrecision))
{
int precArg = Marshal.ReadInt32(args, offset);
objects.Add(precArg);
offset += Marshal.SizeOf(typeof(IntPtr));
}
int iSize = info.flags.HasFlag(Printf.FormatFlags.IsLongLong)
? Marshal.SizeOf(typeof(Int64)) : Marshal.SizeOf(typeof(IntPtr));
// marshal objects from pointer
switch (info.type)
{
// 8/16-bit integers
// char / wchar_t (promoted to int)
case 'c':
char c = (char)Marshal.ReadByte(args, offset);
objects.Add(c);
//offset += Marshal.SizeOf(typeof(Int32));
offset += Marshal.SizeOf(typeof(IntPtr));
break;
// signed integers
case 'd':
case 'i':
{
if (info.flags.HasFlag(Printf.FormatFlags.IsShort)) // h
{
short sh = (short)Marshal.ReadInt32(args, offset);
objects.Add(sh);
offset += Marshal.SizeOf(typeof(Int32));
}
else if (info.flags.HasFlag(Printf.FormatFlags.IsLongLong)) // ll
{
long l = Marshal.ReadInt64(args, offset);
objects.Add(l);
offset += iSize;
}
else // int and long types
{
var i = Marshal.ReadInt32(args, offset);
objects.Add(i);
offset += iSize;
}
}
break;
// unsigned integers
case 'u':
case 'o':
case 'x':
case 'X':
{
if (info.flags.HasFlag(Printf.FormatFlags.IsShort)) // h
{
ushort su = (ushort)Marshal.ReadInt32(args, offset);
objects.Add(su);
offset += Marshal.SizeOf(typeof(Int32));
}
else if (info.flags.HasFlag(Printf.FormatFlags.IsLongLong)) // ll
{
ulong lu = (ulong)(long)Marshal.ReadInt64(args, offset);
objects.Add(lu);
offset += iSize;
}
else // uint and ulong types
{
uint u = (uint)Marshal.ReadInt32(args, offset);
objects.Add(u);
offset += iSize;
}
}
break;
// floating-point types
case 'f':
case 'F':
case 'e':
case 'E':
case 'g':
case 'G':
{
if (info.flags.HasFlag(Printf.FormatFlags.IsLongDouble)) // L
{
// not really supported but read it as long
long lfi = Marshal.ReadInt64(args, offset);
double d = *(double*)(void*)&lfi;
objects.Add(d);
offset += Marshal.SizeOf(typeof(double));
}
else // double
{
long lfi = Marshal.ReadInt64(args, offset);
double d = *(double*)(void*)&lfi;
objects.Add(d);
offset += Marshal.SizeOf(typeof(double));
}
}
break;
// string
case 's':
{
string s = null;
// same:
//var addr1 = new IntPtr(args.ToInt64() + offset);
//var intPtr4 = Marshal.ReadIntPtr(addr1);
var intPtr3 = Marshal.ReadIntPtr(args, offset);
if (info.flags.HasFlag(Printf.FormatFlags.IsLong))
{
s = Marshal.PtrToStringUni(intPtr3);
}
else
{
s = Marshal.PtrToStringAnsi(intPtr3);
}
objects.Add(s);
offset += Marshal.SizeOf(typeof(IntPtr));
}
break;
// pointer
case 'p':
IntPtr ptr = Marshal.ReadIntPtr(args, offset);
objects.Add(ptr);
offset += Marshal.SizeOf(typeof(IntPtr));
break;
// non-marshallable types, ignored
case ' ':
case '%':
case 'n':
break;
default:
throw new ApplicationException("printf specifier '%" + info.type + "' not supported");
}
}
return objects.ToArray();
}
}

Formatting numbers with significant figures in C#

I have some decimal data that I am pushing into a SharePoint list where it is to be viewed. I'd like to restrict the number of significant figures displayed in the result data based on my knowledge of the specific calculation. Sometimes it'll be 3, so 12345 will become 12300 and 0.012345 will become 0.0123. Occasionally it will be 4 or 5. Is there any convenient way to handle this?

See: RoundToSignificantFigures by "P Daddy".
I've combined his method with another one I liked.
Rounding to significant figures is a lot easier in TSQL where the rounding method is based on rounding position, not number of decimal places - which is the case with .Net math.round. You could round a number in TSQL to negative places, which would round at whole numbers - so the scaling isn't needed.
Also see this other thread. Pyrolistical's method is good.
The trailing zeros part of the problem seems like more of a string operation to me, so I included a ToString() extension method which will pad zeros if necessary.
using System;
using System.Globalization;
public static class Precision
{
// 2^-24
public const float FLOAT_EPSILON = 0.0000000596046448f;
// 2^-53
public const double DOUBLE_EPSILON = 0.00000000000000011102230246251565d;
public static bool AlmostEquals(this double a, double b, double epsilon = DOUBLE_EPSILON)
{
// ReSharper disable CompareOfFloatsByEqualityOperator
if (a == b)
{
return true;
}
// ReSharper restore CompareOfFloatsByEqualityOperator
return (System.Math.Abs(a - b) < epsilon);
}
public static bool AlmostEquals(this float a, float b, float epsilon = FLOAT_EPSILON)
{
// ReSharper disable CompareOfFloatsByEqualityOperator
if (a == b)
{
return true;
}
// ReSharper restore CompareOfFloatsByEqualityOperator
return (System.Math.Abs(a - b) < epsilon);
}
}
public static class SignificantDigits
{
public static double Round(this double value, int significantDigits)
{
int unneededRoundingPosition;
return RoundSignificantDigits(value, significantDigits, out unneededRoundingPosition);
}
public static string ToString(this double value, int significantDigits)
{
// this method will round and then append zeros if needed.
// i.e. if you round .002 to two significant figures, the resulting number should be .0020.
var currentInfo = CultureInfo.CurrentCulture.NumberFormat;
if (double.IsNaN(value))
{
return currentInfo.NaNSymbol;
}
if (double.IsPositiveInfinity(value))
{
return currentInfo.PositiveInfinitySymbol;
}
if (double.IsNegativeInfinity(value))
{
return currentInfo.NegativeInfinitySymbol;
}
int roundingPosition;
var roundedValue = RoundSignificantDigits(value, significantDigits, out roundingPosition);
// when rounding causes a cascading round affecting digits of greater significance,
// need to re-round to get a correct rounding position afterwards
// this fixes a bug where rounding 9.96 to 2 figures yeilds 10.0 instead of 10
RoundSignificantDigits(roundedValue, significantDigits, out roundingPosition);
if (Math.Abs(roundingPosition) > 9)
{
// use exponential notation format
// ReSharper disable FormatStringProblem
return string.Format(currentInfo, "{0:E" + (significantDigits - 1) + "}", roundedValue);
// ReSharper restore FormatStringProblem
}
// string.format is only needed with decimal numbers (whole numbers won't need to be padded with zeros to the right.)
// ReSharper disable FormatStringProblem
return roundingPosition > 0 ? string.Format(currentInfo, "{0:F" + roundingPosition + "}", roundedValue) : roundedValue.ToString(currentInfo);
// ReSharper restore FormatStringProblem
}
private static double RoundSignificantDigits(double value, int significantDigits, out int roundingPosition)
{
// this method will return a rounded double value at a number of signifigant figures.
// the sigFigures parameter must be between 0 and 15, exclusive.
roundingPosition = 0;
if (value.AlmostEquals(0d))
{
roundingPosition = significantDigits - 1;
return 0d;
}
if (double.IsNaN(value))
{
return double.NaN;
}
if (double.IsPositiveInfinity(value))
{
return double.PositiveInfinity;
}
if (double.IsNegativeInfinity(value))
{
return double.NegativeInfinity;
}
if (significantDigits < 1 || significantDigits > 15)
{
throw new ArgumentOutOfRangeException("significantDigits", value, "The significantDigits argument must be between 1 and 15.");
}
// The resulting rounding position will be negative for rounding at whole numbers, and positive for decimal places.
roundingPosition = significantDigits - 1 - (int)(Math.Floor(Math.Log10(Math.Abs(value))));
// try to use a rounding position directly, if no scale is needed.
// this is because the scale mutliplication after the rounding can introduce error, although
// this only happens when you're dealing with really tiny numbers, i.e 9.9e-14.
if (roundingPosition > 0 && roundingPosition < 16)
{
return Math.Round(value, roundingPosition, MidpointRounding.AwayFromZero);
}
// Shouldn't get here unless we need to scale it.
// Set the scaling value, for rounding whole numbers or decimals past 15 places
var scale = Math.Pow(10, Math.Ceiling(Math.Log10(Math.Abs(value))));
return Math.Round(value / scale, significantDigits, MidpointRounding.AwayFromZero) * scale;
}
}

This might do the trick:
double Input1 = 1234567;
string Result1 = Convert.ToDouble(String.Format("{0:G3}",Input1)).ToString("R0");
double Input2 = 0.012345;
string Result2 = Convert.ToDouble(String.Format("{0:G3}", Input2)).ToString("R6");
Changing the G3 to G4 produces the oddest result though.
It appears to round up the significant digits?

I ended up snagging some code from http://ostermiller.org/utils/SignificantFigures.java.html. It was in java, so I did a quick search/replace and some resharper reformatting to make the C# build. It seems to work nicely for my significant figure needs. FWIW, I removed his javadoc comments to make it more concise here, but the original code is documented quite nicely.
/*
* Copyright (C) 2002-2007 Stephen Ostermiller
* http://ostermiller.org/contact.pl?regarding=Java+Utilities
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* See COPYING.TXT for details.
*/
public class SignificantFigures
{
private String original;
private StringBuilder _digits;
private int mantissa = -1;
private bool sign = true;
private bool isZero = false;
private bool useScientificNotation = true;
public SignificantFigures(String number)
{
original = number;
Parse(original);
}
public SignificantFigures(double number)
{
original = Convert.ToString(number);
try
{
Parse(original);
}
catch (Exception nfe)
{
_digits = null;
}
}
public bool UseScientificNotation
{
get { return useScientificNotation; }
set { useScientificNotation = value; }
}
public int GetNumberSignificantFigures()
{
if (_digits == null) return 0;
return _digits.Length;
}
public SignificantFigures SetLSD(int place)
{
SetLMSD(place, Int32.MinValue);
return this;
}
public SignificantFigures SetLMSD(int leastPlace, int mostPlace)
{
if (_digits != null && leastPlace != Int32.MinValue)
{
int significantFigures = _digits.Length;
int current = mantissa - significantFigures + 1;
int newLength = significantFigures - leastPlace + current;
if (newLength <= 0)
{
if (mostPlace == Int32.MinValue)
{
original = "NaN";
_digits = null;
}
else
{
newLength = mostPlace - leastPlace + 1;
_digits.Length = newLength;
mantissa = leastPlace;
for (int i = 0; i < newLength; i++)
{
_digits[i] = '0';
}
isZero = true;
sign = true;
}
}
else
{
_digits.Length = newLength;
for (int i = significantFigures; i < newLength; i++)
{
_digits[i] = '0';
}
}
}
return this;
}
public int GetLSD()
{
if (_digits == null) return Int32.MinValue;
return mantissa - _digits.Length + 1;
}
public int GetMSD()
{
if (_digits == null) return Int32.MinValue;
return mantissa + 1;
}
public override String ToString()
{
if (_digits == null) return original;
StringBuilder digits = new StringBuilder(this._digits.ToString());
int length = digits.Length;
if ((mantissa <= -4 || mantissa >= 7 ||
(mantissa >= length &&
digits[digits.Length - 1] == '0') ||
(isZero && mantissa != 0)) && useScientificNotation)
{
// use scientific notation.
if (length > 1)
{
digits.Insert(1, '.');
}
if (mantissa != 0)
{
digits.Append("E" + mantissa);
}
}
else if (mantissa <= -1)
{
digits.Insert(0, "0.");
for (int i = mantissa; i < -1; i++)
{
digits.Insert(2, '0');
}
}
else if (mantissa + 1 == length)
{
if (length > 1 && digits[digits.Length - 1] == '0')
{
digits.Append('.');
}
}
else if (mantissa < length)
{
digits.Insert(mantissa + 1, '.');
}
else
{
for (int i = length; i <= mantissa; i++)
{
digits.Append('0');
}
}
if (!sign)
{
digits.Insert(0, '-');
}
return digits.ToString();
}
public String ToScientificNotation()
{
if (_digits == null) return original;
StringBuilder digits = new StringBuilder(this._digits.ToString());
int length = digits.Length;
if (length > 1)
{
digits.Insert(1, '.');
}
if (mantissa != 0)
{
digits.Append("E" + mantissa);
}
if (!sign)
{
digits.Insert(0, '-');
}
return digits.ToString();
}
private const int INITIAL = 0;
private const int LEADZEROS = 1;
private const int MIDZEROS = 2;
private const int DIGITS = 3;
private const int LEADZEROSDOT = 4;
private const int DIGITSDOT = 5;
private const int MANTISSA = 6;
private const int MANTISSADIGIT = 7;
private void Parse(String number)
{
int length = number.Length;
_digits = new StringBuilder(length);
int state = INITIAL;
int mantissaStart = -1;
bool foundMantissaDigit = false;
// sometimes we don't know if a zero will be
// significant or not when it is encountered.
// keep track of the number of them so that
// the all can be made significant if we find
// out that they are.
int zeroCount = 0;
int leadZeroCount = 0;
for (int i = 0; i < length; i++)
{
char c = number[i];
switch (c)
{
case '.':
{
switch (state)
{
case INITIAL:
case LEADZEROS:
{
state = LEADZEROSDOT;
}
break;
case MIDZEROS:
{
// we now know that these zeros
// are more than just trailing place holders.
for (int j = 0; j < zeroCount; j++)
{
_digits.Append('0');
}
zeroCount = 0;
state = DIGITSDOT;
}
break;
case DIGITS:
{
state = DIGITSDOT;
}
break;
default:
{
throw new Exception(
"Unexpected character '" + c + "' at position " + i
);
}
}
}
break;
case '+':
{
switch (state)
{
case INITIAL:
{
sign = true;
state = LEADZEROS;
}
break;
case MANTISSA:
{
state = MANTISSADIGIT;
}
break;
default:
{
throw new Exception(
"Unexpected character '" + c + "' at position " + i
);
}
}
}
break;
case '-':
{
switch (state)
{
case INITIAL:
{
sign = false;
state = LEADZEROS;
}
break;
case MANTISSA:
{
state = MANTISSADIGIT;
}
break;
default:
{
throw new Exception(
"Unexpected character '" + c + "' at position " + i
);
}
}
}
break;
case '0':
{
switch (state)
{
case INITIAL:
case LEADZEROS:
{
// only significant if number
// is all zeros.
zeroCount++;
leadZeroCount++;
state = LEADZEROS;
}
break;
case MIDZEROS:
case DIGITS:
{
// only significant if followed
// by a decimal point or nonzero digit.
mantissa++;
zeroCount++;
state = MIDZEROS;
}
break;
case LEADZEROSDOT:
{
// only significant if number
// is all zeros.
mantissa--;
zeroCount++;
state = LEADZEROSDOT;
}
break;
case DIGITSDOT:
{
// non-leading zeros after
// a decimal point are always
// significant.
_digits.Append(c);
}
break;
case MANTISSA:
case MANTISSADIGIT:
{
foundMantissaDigit = true;
state = MANTISSADIGIT;
}
break;
default:
{
throw new Exception(
"Unexpected character '" + c + "' at position " + i
);
}
}
}
break;
case '1':
case '2':
case '3':
case '4':
case '5':
case '6':
case '7':
case '8':
case '9':
{
switch (state)
{
case INITIAL:
case LEADZEROS:
case DIGITS:
{
zeroCount = 0;
_digits.Append(c);
mantissa++;
state = DIGITS;
}
break;
case MIDZEROS:
{
// we now know that these zeros
// are more than just trailing place holders.
for (int j = 0; j < zeroCount; j++)
{
_digits.Append('0');
}
zeroCount = 0;
_digits.Append(c);
mantissa++;
state = DIGITS;
}
break;
case LEADZEROSDOT:
case DIGITSDOT:
{
zeroCount = 0;
_digits.Append(c);
state = DIGITSDOT;
}
break;
case MANTISSA:
case MANTISSADIGIT:
{
state = MANTISSADIGIT;
foundMantissaDigit = true;
}
break;
default:
{
throw new Exception(
"Unexpected character '" + c + "' at position " + i
);
}
}
}
break;
case 'E':
case 'e':
{
switch (state)
{
case INITIAL:
case LEADZEROS:
case DIGITS:
case LEADZEROSDOT:
case DIGITSDOT:
{
// record the starting point of the mantissa
// so we can do a substring to get it back later
mantissaStart = i + 1;
state = MANTISSA;
}
break;
default:
{
throw new Exception(
"Unexpected character '" + c + "' at position " + i
);
}
}
}
break;
default:
{
throw new Exception(
"Unexpected character '" + c + "' at position " + i
);
}
}
}
if (mantissaStart != -1)
{
// if we had found an 'E'
if (!foundMantissaDigit)
{
// we didn't actually find a mantissa to go with.
throw new Exception(
"No digits in mantissa."
);
}
// parse the mantissa.
mantissa += Convert.ToInt32(number.Substring(mantissaStart));
}
if (_digits.Length == 0)
{
if (zeroCount > 0)
{
// if nothing but zeros all zeros are significant.
for (int j = 0; j < zeroCount; j++)
{
_digits.Append('0');
}
mantissa += leadZeroCount;
isZero = true;
sign = true;
}
else
{
// a hack to catch some cases that we could catch
// by adding a ton of extra states. Things like:
// "e2" "+e2" "+." "." "+" etc.
throw new Exception(
"No digits in number."
);
}
}
}
public SignificantFigures SetNumberSignificantFigures(int significantFigures)
{
if (significantFigures <= 0)
throw new ArgumentException("Desired number of significant figures must be positive.");
if (_digits != null)
{
int length = _digits.Length;
if (length < significantFigures)
{
// number is not long enough, pad it with zeros.
for (int i = length; i < significantFigures; i++)
{
_digits.Append('0');
}
}
else if (length > significantFigures)
{
// number is too long chop some of it off with rounding.
bool addOne; // we need to round up if true.
char firstInSig = _digits[significantFigures];
if (firstInSig < '5')
{
// first non-significant digit less than five, round down.
addOne = false;
}
else if (firstInSig == '5')
{
// first non-significant digit equal to five
addOne = false;
for (int i = significantFigures + 1; !addOne && i < length; i++)
{
// if its followed by any non-zero digits, round up.
if (_digits[i] != '0')
{
addOne = true;
}
}
if (!addOne)
{
// if it was not followed by non-zero digits
// if the last significant digit is odd round up
// if the last significant digit is even round down
addOne = (_digits[significantFigures - 1] & 1) == 1;
}
}
else
{
// first non-significant digit greater than five, round up.
addOne = true;
}
// loop to add one (and carry a one if added to a nine)
// to the last significant digit
for (int i = significantFigures - 1; addOne && i >= 0; i--)
{
char digit = _digits[i];
if (digit < '9')
{
_digits[i] = (char) (digit + 1);
addOne = false;
}
else
{
_digits[i] = '0';
}
}
if (addOne)
{
// if the number was all nines
_digits.Insert(0, '1');
mantissa++;
}
// chop it to the correct number of figures.
_digits.Length = significantFigures;
}
}
return this;
}
public double ToDouble()
{
return Convert.ToDouble(original);
}
public static String Format(double number, int significantFigures)
{
SignificantFigures sf = new SignificantFigures(number);
sf.SetNumberSignificantFigures(significantFigures);
return sf.ToString();
}
}

I have a shorted answer to calculating significant figures of a number. Here is the code & the test results...
using System;
using System.Collections.Generic;
namespace ConsoleApplicationRound
{
class Program
{
static void Main(string[] args)
{
//char cDecimal = '.'; // for English cultures
char cDecimal = ','; // for German cultures
List<double> l_dValue = new List<double>();
ushort usSignificants = 5;
l_dValue.Add(0);
l_dValue.Add(0.000640589);
l_dValue.Add(-0.000640589);
l_dValue.Add(-123.405009);
l_dValue.Add(123.405009);
l_dValue.Add(-540);
l_dValue.Add(540);
l_dValue.Add(-540911);
l_dValue.Add(540911);
l_dValue.Add(-118.2);
l_dValue.Add(118.2);
l_dValue.Add(-118.18);
l_dValue.Add(118.18);
l_dValue.Add(-118.188);
l_dValue.Add(118.188);
foreach (double d in l_dValue)
{
Console.WriteLine("d = Maths.Round('" +
cDecimal + "', " + d + ", " + usSignificants +
") = " + Maths.Round(
cDecimal, d, usSignificants));
}
Console.Read();
}
}
}
The Maths class used is as follows:
using System;
using System.Text;
namespace ConsoleApplicationRound
{
class Maths
{
/// <summary>
/// The word "Window"
/// </summary>
private static String m_strZeros = "000000000000000000000000000000000";
/// <summary>
/// The minus sign
/// </summary>
public const char m_cDASH = '-';
/// <summary>
/// Determines the number of digits before the decimal point
/// </summary>
/// <param name="cDecimal">
/// Language-specific decimal separator
/// </param>
/// <param name="strValue">
/// Value to be scrutinised
/// </param>
/// <returns>
/// Nr. of digits before the decimal point
/// </returns>
private static ushort NrOfDigitsBeforeDecimal(char cDecimal, String strValue)
{
short sDecimalPosition = (short)strValue.IndexOf(cDecimal);
ushort usSignificantDigits = 0;
if (sDecimalPosition >= 0)
{
strValue = strValue.Substring(0, sDecimalPosition + 1);
}
for (ushort us = 0; us < strValue.Length; us++)
{
if (strValue[us] != m_cDASH) usSignificantDigits++;
if (strValue[us] == cDecimal)
{
usSignificantDigits--;
break;
}
}
return usSignificantDigits;
}
/// <summary>
/// Rounds to a fixed number of significant digits
/// </summary>
/// <param name="d">
/// Number to be rounded
/// </param>
/// <param name="usSignificants">
/// Requested significant digits
/// </param>
/// <returns>
/// The rounded number
/// </returns>
public static String Round(char cDecimal,
double d,
ushort usSignificants)
{
StringBuilder value = new StringBuilder(Convert.ToString(d));
short sDecimalPosition = (short)value.ToString().IndexOf(cDecimal);
ushort usAfterDecimal = 0;
ushort usDigitsBeforeDecimalPoint =
NrOfDigitsBeforeDecimal(cDecimal, value.ToString());
if (usDigitsBeforeDecimalPoint == 1)
{
usAfterDecimal = (d == 0)
? usSignificants
: (ushort)(value.Length - sDecimalPosition - 2);
}
else
{
if (usSignificants >= usDigitsBeforeDecimalPoint)
{
usAfterDecimal =
(ushort)(usSignificants - usDigitsBeforeDecimalPoint);
}
else
{
double dPower = Math.Pow(10,
usDigitsBeforeDecimalPoint - usSignificants);
d = dPower*(long)(d/dPower);
}
}
double dRounded = Math.Round(d, usAfterDecimal);
StringBuilder result = new StringBuilder();
result.Append(dRounded);
ushort usDigits = (ushort)result.ToString().Replace(
Convert.ToString(cDecimal), "").Replace(
Convert.ToString(m_cDASH), "").Length;
// Add lagging zeros, if necessary:
if (usDigits < usSignificants)
{
if (usAfterDecimal != 0)
{
if (result.ToString().IndexOf(cDecimal) == -1)
{
result.Append(cDecimal);
}
int i = (d == 0) ? 0 : Math.Min(0, usDigits - usSignificants);
result.Append(m_strZeros.Substring(0, usAfterDecimal + i));
}
}
return result.ToString();
}
}
}
Any answer with a shorter code?

You can get an elegant bit perfect rounding by using the GetBits method on Decimal and leveraging BigInteger to perform masking.
Some utils
public static int CountDigits
(BigInteger number) => ((int)BigInteger.Log10(number))+1;
private static readonly BigInteger[] BigPowers10
= Enumerable.Range(0, 100)
.Select(v => BigInteger.Pow(10, v))
.ToArray();
The main function
public static decimal RoundToSignificantDigits
(this decimal num,
short n)
{
var bits = decimal.GetBits(num);
var u0 = unchecked((uint)bits[0]);
var u1 = unchecked((uint)bits[1]);
var u2 = unchecked((uint)bits[2]);
var i = new BigInteger(u0)
+ (new BigInteger(u1) << 32)
+ (new BigInteger(u2) << 64);
var d = CountDigits(i);
var delta = d - n;
if (delta < 0)
return num;
var scale = BigPowers10[delta];
var div = i/scale;
var rem = i%scale;
var up = rem > scale/2;
if (up)
div += 1;
var shifted = div*scale;
bits[0] =unchecked((int)(uint) (shifted & BigUnitMask));
bits[1] =unchecked((int)(uint) (shifted>>32 & BigUnitMask));
bits[2] =unchecked((int)(uint) (shifted>>64 & BigUnitMask));
return new decimal(bits);
}
test case 0
public void RoundToSignificantDigits()
{
WMath.RoundToSignificantDigits(0.0012345m, 2).Should().Be(0.0012m);
WMath.RoundToSignificantDigits(0.0012645m, 2).Should().Be(0.0013m);
WMath.RoundToSignificantDigits(0.040000000000000008, 6).Should().Be(0.04);
WMath.RoundToSignificantDigits(0.040000010000000008, 6).Should().Be(0.04);
WMath.RoundToSignificantDigits(0.040000100000000008, 6).Should().Be(0.0400001);
WMath.RoundToSignificantDigits(0.040000110000000008, 6).Should().Be(0.0400001);
WMath.RoundToSignificantDigits(0.20000000000000004, 6).Should().Be(0.2);
WMath.RoundToSignificantDigits(0.10000000000000002, 6).Should().Be(0.1);
WMath.RoundToSignificantDigits(0.0, 6).Should().Be(0.0);
}
test case 1
public void RoundToSigFigShouldWork()
{
1.2m.RoundToSignificantDigits(1).Should().Be(1m);
0.01235668m.RoundToSignificantDigits(3).Should().Be(0.0124m);
0.01m.RoundToSignificantDigits(3).Should().Be(0.01m);
1.23456789123456789123456789m.RoundToSignificantDigits(4)
.Should().Be(1.235m);
1.23456789123456789123456789m.RoundToSignificantDigits(16)
.Should().Be(1.234567891234568m);
1.23456789123456789123456789m.RoundToSignificantDigits(24)
.Should().Be(1.23456789123456789123457m);
1.23456789123456789123456789m.RoundToSignificantDigits(27)
.Should().Be(1.23456789123456789123456789m);
}

I found this article doing a quick search on it. Basically this one converts to a string and goes by the characters in that array one at a time, till it reached the max. significance. Will this work?

The following code doesn't quite meet the spec, since it doesn't try to round anything to the left of the decimal point. But it's simpler than anything else presented here (so far). I was quite surprised that C# doesn't have a built-in method to handle this.
static public string SignificantDigits(double d, int digits=10)
{
int magnitude = (d == 0.0) ? 0 : (int)Math.Floor(Math.Log10(Math.Abs(d))) + 1;
digits -= magnitude;
if (digits < 0)
digits = 0;
string fmt = "f" + digits.ToString();
return d.ToString(fmt);
}

This method is dead simple and works with any number, positive or negative, and only uses a single transcendental function (Log10). The only difference (which may/may-not matter) is that it will not round the integer component. This is perfect however for currency processing where you know the limits are within certain bounds, because you can use doubles for much faster processing than the dreadfully slow Decimal type.
public static double ToDecimal( this double x, int significantFigures = 15 ) {
// determine # of digits before & after the decimal
int digitsBeforeDecimal = (int)x.Abs().Log10().Ceil().Max( 0 ),
digitsAfterDecimal = (significantFigures - digitsBeforeDecimal).Max( 0 );
// round it off
return x.Round( digitsAfterDecimal );
}

As I remember it "significant figures" means the number of digits after the dot separator so 3 significant digits for 0.012345 would be 0.012 and not 0.0123, but that really doesnt matter for the solution.
I also understand that you want to "nullify" the last digits to a certain degree if the number is > 1. You write that 12345 would become 12300 but im not sure whether you want 123456 to become 1230000 or 123400 ? My solution does the last. Instead of calculating the factor you could ofcourse make a small initialized array if you only have a couple of variations.
private static string FormatToSignificantFigures(decimal number, int amount)
{
if (number > 1)
{
int factor = Factor(amount);
return ((int)(number/factor)*factor).ToString();
}
NumberFormatInfo nfi = new CultureInfo("en-US", false).NumberFormat;
nfi.NumberDecimalDigits = amount;
return(number.ToString("F", nfi));
}
private static int Factor(int x)
{
return DoCalcFactor(10, x-1);
}
private static int DoCalcFactor(int x, int y)
{
if (y == 1) return x;
return 10*DoCalcFactor(x, y - 1);
}
Kind regards
Carsten