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Getting an System.FormatException in C#

I am new so I don't know why I am getting such an exception and also I don't know how to explain so here is the code
using System;
namespace math
{
class Math
{
int add(int a, int b)
{
return a + b;
}
static void Main(string[] args)
{
Math math = new Math();
int result = 0;
for (int i = 0; i < args.Length; i++)
{
switch(args[i])
{
case "+":
result = math.add(int.Parse(args[i--]), int.Parse(args[i++]));
break;
default:
break;
}
}
Console.WriteLine(result);
Console.ReadLine();
}
}
}
this is the whole exception from VS Code
Exception has occurred: CLR/System.FormatException
An unhandled exception of type 'System.FormatException' occurred in System.Private.CoreLib.dll: 'Input string was not in a correct format.'
at System.Number.ThrowOverflowOrFormatException(ParsingStatus status, TypeCode type)
at System.Number.ParseInt32(ReadOnlySpan`1 value, NumberStyles styles, NumberFormatInfo info)
at System.Int32.Parse(String s)
at math.Math.Main(String[] args) in D:\tmp\math\Program.cs:line 20
Edit : This is a command line program like "whoami" or like "g++"?

You are modifying your loop index here:
result = math.add(int.Parse(args[i--]), int.Parse(args[i++]));
This will result in you reading the "+" again rather than the numbers you're expecting, which is why you're getting the FormatException.
Change the line to:
result = math.add(int.Parse(args[i - 1]), int.Parse(args[i + 1]));
This is easier to understand and doesn't mess with the loop index.
This will still fail if someone enters "a + b" (say), so you should really check that the values are integers:
int first;
int second;
if (int.TryParse(args[i-1], out first) &&
int.TryParse(args[i+1], out second))
{
result = first + second;
}
else
{
// Error: both values need to be numeric
}

Following would be an simple alternative to start with if it is C#.
class Math
{
int add(int a, int b)
{
return a + b;
}
static void Main(string[] args)
{
Math math = new Math();
Console.Write("Enter Integer: ");
var val1 = Console.ReadLine();
int a = Convert.ToInt32(val1);
Console.Write("Enter Integer: ");
var val2 = Console.ReadLine();
int b = Convert.ToInt32(val2);
Console.Write("Enter Operation: ");
var operation = Console.ReadLine();
int result = 0;
switch(operation)
{
case "+":
result = math.add(a, b);
break;
default:
break;
}
Console.WriteLine(result);
Console.ReadLine();
}
}

eliminate line break after read in C#

using A = System.Console;
public void point()
{
int hour, minute;
A.Write("Enter Time (HH:MM) = ");
hour = A.Read();
A.Write(":");
minute = A.Read();
}
I want it to be like
"Enter Time (HH:MM) = 12(hour input):49(minute input)"
but it coming like
"Enter Time (HH:MM) = 12(hour input)
:49(minute input)

Simplest way (assuming you are reading from Console, and user will enter hour then press Enter, then enter minute and press Enter):
static void Main(string[] args)
{
int hour = 0, minute = 0;
const int MAX_NUMBER_OF_DIGITS = 2 ;
Console.Write("Enter Time (HH:MM) = ");
// store cursor position
int cursorLeft = Console.CursorLeft;
int cursorTop = Console.CursorTop;
// use ReadLine, else you will only get 1 character
// i.e. number more than 1 digits will not work
hour = int.Parse(Console.ReadLine());
Console.SetCursorPosition(cursorLeft + MAX_NUMBER_OF_DIGITS , cursorTop);
Console.Write(":");
minute = int.Parse(Console.ReadLine());
// Nitpickers! purposefully not using String.Format,
// or $, since want to keep it simple!
Console.Write("You entered: " + hour + ":" + minute);
}
Output:
Enter Time (HH:MM) = 17:55
You entered: 17:55
Though I would rather recommend you better and less error prone way like this (where user inputs HH:MM and presses Enter a single time i.e. enters a single string including : i.e. colon):
static void Main(string[] args)
{
int hour = 0, minute = 0;
Console.Write("Enter Time in format HH:MM = ");
string enteredNumber = Console.ReadLine();
string[] aryNumbers = enteredNumber.Split(':');
if (aryNumbers.Length != 2)
{
Console.Write("Invalid time entered!");
}
else
{
hour = int.Parse(aryNumbers[0]);
minute = int.Parse(aryNumbers[1]);
// Nitpickers! purposefully not using String.Format,
// or $, since want to keep it simple!
Console.Write("You entered: " + hour + ":" + minute);
}
}

Assuming that A is Console, you can do like this:
static void Main()
{
int hour, minute;
char[] hourChars = new char[2];
Console.Write("Enter Time (HH:MM) = ");
hourChars[0] = Console.ReadKey().KeyChar;
hourChars[1] = Console.ReadKey().KeyChar;
var hourString = new String(hourChars);
hour = int.Parse(hourString);
Console.Write(":");
minute = Console.Read();
}

Assuming A is the standard c# Console then you can use ReadKey instead of Read
ReadKey will read only one character at a time but it will not force you to hit enter which is the cause for the new line.
static void Main()
{
char h1, h2, m1, m2;
Console.Write("Enter Time (HH:MM) = ");
h1 = Console.ReadKey().KeyChar;
h2 = Console.ReadKey().KeyChar;
Console.Write(":");
m1 = Console.ReadKey().KeyChar;
m2 = Console.ReadKey().KeyChar;
}
I will leave the actual value parsing as an exercise.

C# How do I error check the input ensuring only integers between 1-100 are accepted

I'm creating a program for a college assignment and the task is to create a program that basically creates random times table questions. I have done that, but need to error check the input to only accept integer inputs between 1-100. I can not find anything online only for like java or for text box using OOP.
Here is my code:
static void help()
{
Console.WriteLine("This program is to help children learn how to multiply");
Console.WriteLine("The program will create times table questions from 1-10");
Console.WriteLine("The user will be given 10 random questions to complete");
Console.WriteLine("The user will get a score out of 10 at the end");
Console.WriteLine("If the user gets the answer wrong, the correct answer will be displayed");
Console.WriteLine("");
Console.ReadLine();
Console.Clear();
}
static void Main(string[] args)
{
int Random1 = 0;
int Random2 = 0;
int Answer;
int Count = 0;
int Score = 0;
int input = 0;
String choice;
Console.WriteLine("To begin the Maths test please hit any key");
Console.WriteLine("If you need any help, just, type help");
choice = Console.ReadLine();
if (choice == "help")
{
help();
}
while (Count != 10)
{
Random numbers = new Random();
Random1 = numbers.Next(0, 11);
Count = Count + 1;
Random numbers2 = new Random();
Random2 = numbers.Next(0, 11);
Console.WriteLine(Random1 + "x" + Random2 + "=");
input = int.Parse(Console.ReadLine());
Answer = Random1 * Random2;
if (Answer == input)
{
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("Correct");
Score = Score + 1;
Console.ResetColor();
}
else
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("Thats the wrong answer, the correct is " + Answer);
Console.ResetColor();
}
}
if (Score > 5)
{
Console.ForegroundColor = ConsoleColor.Green;
Console.WriteLine("Good job you got more than 5 answers correct! With a score of " + Score + " out of 10");
Console.ResetColor();
Console.ReadLine();
}
else if (Score < 5)
{
Console.ForegroundColor = ConsoleColor.Red;
Console.WriteLine("");
Console.WriteLine("Try again you got less than 5 correct! With a score of " + Score + " out of 10");
Console.ResetColor();
Console.ReadLine();
}
}
}
}

Firstly, I suggest you to use TryParse instead of Parse to prevent unexpected errors because of invalid inputs. So, try something like that;
Random numbers = new Random();
Random1 = numbers.Next(0, 11);
Count = Count + 1;
Random numbers2 = new Random();
Random2 = numbers.Next(0, 11);
Console.WriteLine(Random1 + "x" + Random2 + "=");
//Modified
int input = 0;
while (true)
{
if (!int.TryParse(Console.ReadLine(), out input))
{
Console.WriteLine("Invalid Input. Please enter a valid integer.");
}
else
{
if (input >= 1 && input <= 100)
{
break;
}
Console.WriteLine("Invalid Input. Please enter a integer between 1-100.");
}
}
//Modified

I'd simply use a loop that will keep asking for input until it
matches your requirement:
int MinVal = 1; // No magic numbers! You may consider placing them in a config
int MaxVal = 100; // or as static readonly class members (a bit like "const").
int input = -1;
for(;;) // "empty" for-loop = infinite loop. No problem, we break on condition inside.
{
// attempt getting input from user
bool parseOK = int.TryParse(Console.ReadLine(), out input);
// Exit loop if input is valid.
if( parseOK && input >= MinVal && input <= MaxVal ) break;
Console.WriteLine( "Errormessage telling user what you expect" );
}
You may also consider granting only N trys to get the input right.
A few hints:
do not use "magic numbers". Define constants or put numbers into Properties/Settings. Name them self-explanatory and document why you chose the value they happen to have.
The errormessage should tell the user what an expected valid input is (as opposed to what they typed in) not just that their input was invalid.

Whats about this?
input = int.Parse(Console.ReadLine());
if(input > 1 && input < 100){
// valid
}else{
// invalid
}

C# converting strings to int's

I'm new to c# and am trying to make a simple calculator.
It works fine until it goes back to the start to take a new number.
When taking the new number it says it cant convert the user input to a integer.
using System;
namespace simpleCalculator
{
class MainClass
{
public static void Main(string[] args)
{
start:
Console.Clear();
Console.WriteLine("Enter first number");
int x = Convert.ToConsole.ReadLine();
Console.WriteLine("Would you like to\n1. Add\n2. Multiply\n3. Devide");
string o = Console.ReadLine();
if (o == "1")
{
Console.WriteLine("Enter second number\n");
int y = Convert.ToInt32(Console.ReadLine());
add(temp, y);
goto start;
Console.Clear();
goto start;
}
}
public static void add(int num01, int num02)
{
Console.Clear();
Console.WriteLine((num01 + num02) + "\nPress enter to contiue.");
Console.Read();
}
}
}

Use TryParse so if the parsing fails, you will not get an exception.
var enteredValue = Console.ReadLine();
var parsedValue;
if (!int.TryParse(enteredValue, out parsedValue))
{
// parse failed do whatever you want
}
Do that for both entries and if both of them pass, then call your add method.

You're looking for int.Parse(). Be careful to validate your input. You should probably create an escape condition.
Edited to show an alternative solution
Edited to be more explicit on how to handle some input
class Program
{
public static void Main(string[] args)
{
string input = String.Empty;
int x = 0, y = 0;
while (true)
{
try
{
Console.WriteLine("Enter first number");
x = int.Parse(Console.ReadLine());
Console.WriteLine("Would you like to\n1. Add\n2. Multiply\n3. Divide");
input = Console.ReadLine();
Console.WriteLine("Please enter a second number");
y = int.Parse(Console.ReadLine());
}
catch
{
Console.WriteLine("Invalid input");
continue;
}
switch (input)
{
case "1":
Console.WriteLine($"{x} + {y} = " + add(x, y));
break;
case "2":
//TODO implement multiply case
break;
case "3":
//TODO implement divide case
break;
default:
Console.WriteLine("Invalid input");
break;
}
}
}
public static int add(int x, int y) => x + y;
}

Try this:
int numbers = Convert.ToInt32("1234");

How do I prevent crashing due to invalid input in C#?

The program I've written is set to only accept positive integers as input. If the user inputs a letter instead, then it crashes. Negative integers don't cause any problems, though it's not 'valid' in regards to how my program functions.
What I want to do is:
Prevent the program from crashing from invalid input.
Display an error message if the input is invalid
Have the program continue where it left off, without affecting the rest of the program.
Also, a part of my program involves division. Is there a way to prevent the user from entering all zeros?
This is in C#
My code:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace OverallCalculator
{
class Program
{
static void Main(string[] args)
{
bool shouldContinue;
do
{
Console.WriteLine("Enter Striking Level: ");
string striking = Console.ReadLine();
Console.WriteLine("Enter Grappling Level: ");
string grappling = Console.ReadLine();
Console.WriteLine("Enter Submission Level: ");
string submission = Console.ReadLine();
Console.WriteLine("Enter Durability Level: ");
string durability = Console.ReadLine();
Console.WriteLine("Enter Technical Level: ");
string technical = Console.ReadLine();
Console.WriteLine("Enter Speed Level: ");
string speed = Console.ReadLine();
Console.WriteLine("Enter Hardcore Level: ");
string hardcore = Console.ReadLine();
Console.WriteLine("Enter Charisma Level: ");
string charisma = Console.ReadLine();
int gra = Convert.ToInt32(grappling);
int str = Convert.ToInt32(striking);
int dur = Convert.ToInt32(durability);
int spd = Convert.ToInt32(speed);
int tec = Convert.ToInt32(technical);
int hdc = Convert.ToInt32(hardcore);
int cha = Convert.ToInt32(charisma);
int sub = Convert.ToInt32(submission);
int total = str + gra + sub + dur + tec + spd + cha + hdc;
int overall = total / 8 + 8;
Console.WriteLine("The Overall is " + overall);
Console.WriteLine("Do you wish to continue? y/n? ");
if (Console.ReadLine() == "y")
{
shouldContinue = true;
}
else break;
} while (shouldContinue == true);
}
}
}

int value = 0;
if (!int.TryParse(input, out value))
{
MessageBox.Show("Oops");
} else {
// use the value in the variable "value".
}

static void Main(string[] args)
{
bool validInput = false;
string inputString;
UInt32 validPositiveInteger = 0;
while (!validInput)
{
Console.WriteLine("Please enter a positive 32 bit integer:");
inputString = Console.ReadLine();
if (!UInt32.TryParse(inputString, out validPositiveInteger))
{
Console.WriteLine("Input was not a positive integer.");
}
else if (validPositiveInteger.Equals(0))
{
Console.WriteLine("You cannot enter zero.");
}
else
{
validInput = true;
//Or you could just break
//break;
}
}
Console.WriteLine(String.Format("Positive integer = {0}", validPositiveInteger));
}

Here you go:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
namespace OverallCalculator
{
class Program
{
static void Main(string[] args)
{
bool shouldContinue = true;
while (shouldContinue)
{
int strikingLevel = GetValue("Enter Striking Level: ");
int grapplingLevel = GetValue("Enter Grappling Level: ");
int submissionLevel = GetValue("Enter Submission Level: ");
int durabilityLevel = GetValue("Enter Durability Level: ");
int technicalLevel = GetValue("Enter Technical Level: ");
int speedLevel = GetValue("Enter Speed Level: ");
int hardcoreLevel = GetValue("Enter Hardcore Level: ");
int charismaLevel = GetValue("Enter Charisma Level: ");
int total = strikingLevel + grapplingLevel + durabilityLevel + submissionLevel +
technicalLevel + speedLevel + charismaLevel + hardcoreLevel;
int overall = total / 8 + 8;
Console.WriteLine("\nThe Overall is {0}.", overall);
while (true)
{
Console.WriteLine("Do you wish to continue? y/n? ");
string response = Console.ReadLine();
if (response.Equals("y", StringComparison.CurrentCultureIgnoreCase) ||
response.Equals("yes", StringComparison.CurrentCultureIgnoreCase))
{
shouldContinue = true;
break;
}
else if (response.Equals("n", StringComparison.CurrentCultureIgnoreCase) ||
response.Equals("no", StringComparison.CurrentCultureIgnoreCase))
{
shouldContinue = false;
break;
}
}
}
}
private static int GetValue(string prompt)
{
while (true)
{
Console.WriteLine(prompt);
string input = Console.ReadLine();
int value;
if (int.TryParse(input, out value))
{
if (value <= 0)
Console.WriteLine("Please enter a positive number.");
else
return value;
}
else
{
Console.WriteLine("Please enter a number.");
}
}
}
}
}

Yes... before you do anything calculations, you need to validate the data you are going to use. If any data is incorrect, then you display a messagebox detailing the errors and return focus to the form so the user can fix the errors. Repeat as necessary.

I wrote this one many moons ago when I first learned C#. It is a conversion from a VB function that I got back in VB5 days. The major benefit of the function is that there is no error - an input will just not allow any characters outside of the predefined list.
/***********************************************************************
* bool ValiText(char inChar,
* string valid,
* bool editable,
* bool casesensitive
* Description: Validate Input Characters As They Are Input
* Notes: For each control whose input you wish to validate, just put
* e.Handled = ValiText(e.KeyChar, "0123456789/-" [,true][,true])
* In The KeyPress Event
***********************************************************************/
public bool ValiText(char inChar, string valid, bool editable, bool casesensitive)
{
string inVal = inChar.ToString();
string tst = valid;
/// Editable - Add The Backspace Key
if (editable) tst += ((char)8).ToString();
/// Case InSensitive - Make Them Both The Same Case
if (!casesensitive)
{
tst = tst.ToLower();
inVal = inVal.ToLower();
}
return tst.IndexOf(inVal,0,tst.Length) < 0;
}
public bool ValiText(char inChar, string valid, bool editable)
{
string tst = valid;
/// Editable - Add The Backspace Key
if (editable) tst += ((char)8).ToString();
return tst.IndexOf(inChar.ToString(),0,tst.Length) < 0;
}
public bool ValiText(char inChar, string valid)
{
return valid.IndexOf(inChar.ToString(),0,valid.Length) < 0;
}
Note That This Will Not Work On A Web APP.