I just wrote my first C# console application, I am still a beginner. Anyway, I tried the code below and it seems to work, its for solving quadratic equations. I'd like to add code for a situation whereby a user inputs a string instead of an integer and give an error message any ideas as to how to implement this?
namespace Quadratic_equation
{
class Program
{
static void Main(string[] args)
{
Console.WriteLine("welcome to seyi's quadratic calculator!!!");
Console.Write("a:");
double a = Convert.ToInt32(Console.ReadLine());
Console.Write("b:");
double b = Convert.ToInt32(Console.ReadLine());
Console.Write("c:");
double c = Convert.ToInt32(Console.ReadLine());
if ((b * b - 4 * a * c) < 0) {
Console.WriteLine("There are no real roots!");
}
else {
double x1 = (-b + Math.Sqrt((b*b)-4*a*c)) /2*a;
double x2 = (-b + Math.Sqrt((b*b)-4*a*c)) /2*a;
Console.WriteLine("x:{0}",x1);
Console.WriteLine("y:{0}",x2);
}
Console.ReadKey();
}
}
}
You can use Int32.TryParse method to check your string is a valid integer or not. This method returns a boolean value for your conversation is succeed or not.
Converts the string representation of a number to its 32-bit signed
integer equivalent. A return value indicates whether the conversion
succeeded.
And I don't understand why you want to keep as double the return value of Convert.ToInt32 method. These factors (a, b, c) should be integer, not double.
int a;
string s = Console.ReadLine();
if(Int32.TryParse(s, out a))
{
// Your input string is a valid integer.
}
else
{
// Your input string is not a valid integer.
}
This Int32.TryParse(string, out int) overload uses NumberStyle.Integer as default. That means your string can have one of these;
Trailing white spaces
Leading white spaces
Leading sign character
Check out int.TryParse
int number;
bool result = Int32.TryParse(value, out number);
if (result)
{
Console.WriteLine("Converted '{0}' to {1}.", value, number);
}
else
{
if (value == null) value = "";
Console.WriteLine("Attempted conversion of '{0}' failed.", value);
}
Use a try-catch block in a do-while loop:
bool goToNextNum = false;
do
{
try
{
double a = Convert.ToInt32(Console.ReadLine());
goToNextNum = true;
}
catch
{
Console.WriteLine("Invalid Number");
}
} while (goToNextNum == false);
This will loop until a is a valid number.
Related
Can someone help me modify my work? Help me add:
An error message when the user tries to enter decimal values.
A third operand for the calculator.
An error message when the user tries to enter any string value other than “exit”.
Here's my code:
class Program
{
static void Main(string[] args)
{
do
{
Console.Write("x = ");
string str = Console.ReadLine();
if (str == "exit")
{
Console.WriteLine("The Programme has stopped");
continue;
}
else
{
int x = Convert.ToInt32(str);
Console.Write("y = ");
int y = Convert.ToInt32(Console.ReadLine());
int sum = x / y;
Console.WriteLine("Result: {0}", sum);
}
}
while (true);
}
}
I'd be very grateful.
Here is a function you can use:
public static bool HasDecimals(decimal x) {
return Decimal.Round(x, 0) != x;
}
If I were going to do this, I'd create a function that I can use to handle most of the user interaction (emitting the prompt, parsing the input string, deciding if "Exit" was entered). In the code below, I kinda-sorta use the standard TryGetXxx pattern.
In this code below, if the TryGetDecimalValueWithPrompt returns true, then a properly parsed number is returned in the output. If it returns false, then the user has chosen to quit.
So, I start with that function:
public static bool TryGetDecimalValueWithPrompt(string prompt, out decimal outputValue)
{
while (true)
{
Console.Write(prompt + " > ");
var response = Console.ReadLine();
if (response.Equals("exit", StringComparison.OrdinalIgnoreCase) || response.Equals("quit", StringComparison.OrdinalIgnoreCase))
{
outputValue = 0.0m;
return false;
}
if (decimal.TryParse(response, out outputValue))
{
return true;
}
//otherwise, failure, so try again
Console.WriteLine("Sorry, incorrect format, try entering a correctly formatted decimal again");
}
}
The while(true) statement says Loop Forever. In this case, Forever lasts until the user has entered a properly formatted number or one of the "exit" keywords.
Then I construct my program around it:
if (!TryGetDecimalValueWithPrompt("Enter the first operand", out var operand1))
{
return;
}
if (!TryGetDecimalValueWithPrompt("Enter the second operand", out var operand2))
{
return;
}
if (operand2 == 0.0m)
{
Console.WriteLine("Sorry, you can't divide by zero");
return;
}
Console.WriteLine($"The result of op1/op2 is {operand1 / operand2}");
If you don't want to allow decimals being entered, change the TryGetDecimalValueWithPrompt function to work with integers instead:
public static bool TryGetIntValueWithPrompt(string prompt, out int outputValue)
{
while (true)
{
Console.Write(prompt + " > ");
var response = Console.ReadLine();
if (response.Equals("exit", StringComparison.OrdinalIgnoreCase) || response.Equals("quit", StringComparison.OrdinalIgnoreCase))
{
outputValue = 0;
return false;
}
if (int.TryParse(response, out outputValue))
{
return true;
}
//otherwise, failure, so try again
Console.WriteLine("Sorry, incorrect format, try entering a correctly formatted integer again");
}
}
If you work with integers, remember that integer division always yields an integer. For example, if you use integers in 7 / 2, the result will be 3, not 3.5. If you want 3.5, do something like 7 / (decimal) 2 (at that point, you are dividing an integer by a decimal and you'll get a decimal).
By the way, if you wanted to prompt for the operator (+, -, *, or /), you could create a TryGetOperator function in the same pattern and just check whatever you get from the user with something like:
var operators = new[] { "+", "-", "*", "/" };
bool goodOperator = operators.Contains(inputFromUser);
I have to write a code that will ask for 3 integers values and find the greatest one. However, if the user enters a non numeric value this must have the value of zero. So far i wrote this
int a, b, c;
Console.WriteLine("Enter value 1:");
a = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Enter value 2:");
b = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Enter value 3:");
c = Convert.ToInt32(Console.ReadLine());
if (a > b && a > c)
{
Console.WriteLine("The greatest value is: {0}", a);
}
if (b > a && b > c)
{
Console.WriteLine("The greatest value is: {0}", b);
}
if (c > a && c > b)
{
Console.WriteLine("The greatest value is: {0}", c);
}
This code works only with numbers.
My problem is that i can't make a non numeric input have the value of zero.
I tried using string instead of int, so there is no error but i can not make use ">" with strings in the if statements and i also tried using as default, because when is default so it is zero.
Thank you
You can just replace:
x = Convert.ToInt32(Console.ReadLine());
With...
int.TryParse(Console.ReadLine(), out int x);
If the input can't be parsed, x will end up being 0.
I think you can create a function that does the try catch, in this way you print a message saying that the input was not a number.
static int Check(string input)
{
int result;
try
{
result = Convert.ToInt32(input);
}
catch (FormatException e)
{
Console.WriteLine("Input not integer, the value assigned is 0");
result = 0;
}
return result;
}
For implementing you just call:
a = Check(Console.ReadLine());
This question already has answers here:
C# compiler error: "not all code paths return a value"
(9 answers)
Closed 3 years ago.
I don't want the else statement to return a value, but just run the method again. However, I get compile time error
'Program.Coefficient()': not all code paths return a value.
How do I get rid of this error?
This is the code:
public static double Coefficient()
{
string string1 = Console.ReadLine();
string[] stringArray = string1.Split('^');
double[] doubleArray = new double[stringArray.Length];
for (int i = 0; i < stringArray.Length; i++)
{
doubleArray[i] = Double.Parse(stringArray[i]);
}
if (doubleArray.Length == 2)
{
double coefficient = Math.Pow(doubleArray[0], doubleArray[1]);
return coefficient;
}
else if (doubleArray.Length == 1)
{
double coefficient = doubleArray[0];
return coefficient;
}
else
{
Console.WriteLine("Please follow the specified input form (a^b).");
Console.ReadKey();
Coefficient();
}
}
The error means that at least one flow possibility does not return a value, which is the last 'else' in your case.
The last line should be then:
return Coefficient();
As your function returns value, that means from each if..else block you need to return double value.
Here you are not returning any value from else block. You need to return double value from else block
else
{
Console.WriteLine("Please follow the specified input form (a^b).");
Console.ReadKey();
return Coefficient(); // This will call recursively same function. for recursion use return Coefficient() ;
//return 0; //If you don't want recursion, then comment above line and return 0
}
I would prefer to refactor your code to minimize code present in Coefficient() method. something like ,
public static double Coefficient()
{
while (true)
{
string string1 = Console.ReadLine();
string[] stringArray = string1.Split('^');
double[] doubleArray = Array.ConvertAll(stringArray, double.Parse);
if (doubleArray.Length == 2)
{
double coefficient = Math.Pow(doubleArray[0], doubleArray[1]);
return coefficient;
}
else if (doubleArray.Length == 1)
{
return doubleArray[0];
}
Console.WriteLine("Please follow the specified input form (a^b).");
}
}
I suggest to redesign the routine (I can't see any need in recursion). You can implement a loop in order to keep asking until user inputs (Console.ReadLine()) valid value:
public static double Coefficient() {
while (true) {
string input = Console.ReadLine();
string[] items = input.Split('^');
if (items.Length == 1) {
if (double.TryParse(items[0], out double A))
return A; // One valid value
}
else if (items.Length == 2) {
if (double.TryParse(items[0], out double A) &&
double.TryParse(items[1], out double B))
return Math.Pow(A, B); // Two valid values
}
// Neither one valid value, nor two valid values pattern
Console.WriteLine("Please follow the specified input form (a^b).");
// No need in "Console.ReadKey();" - the routine will stop on Console.ReadLine()
}
}
Be careful with Double.Parse since it throws exception on invalid string (e.g. if user inputs "bla-bla-bla"); use Double.TryParse instead.
I want to make a calculator that asks what you want to do, e.g. add, subtract, etc. It should then use if-statements to perform the different kinds of calculations.
But now when I have gotten to division, I'm wondering how to handle division by 0. I want the program to warn the user when he/she enters a 0, saying something like "sorry you can't divide by 0".
I still want it to calculate the result if the denominator isn't 0.
The error i get is that i can't write:
if (Num02 == "0") because I can't use ints or doubles etc.
How do I fix this in a nice way to show my class/teacher next week?
Here's my code:
using System;
namespace Calculator
{
class MainClass
{
static void Main(string[] args)
{
Start:
int Num01;
int Num02;
string Answer;
Console.WriteLine("What do you want to do?");
Answer = Console.ReadLine();
if (Answer == "Division")
{
Console.WriteLine("Write number");
Num01 = Convert.ToInt32(Console.ReadLine());
Console.WriteLine("Divided by?");
Num02 = Convert.ToInt32(Console.ReadLine());
Console.WriteLine(Num01 + "/" + Num02 + "=" +
(Num01 / Num02));
}
}
}
}
the error i seem to get is that i cant write:
"if (num02 == "0")" because i cant use ints or doubles etc.
You were most certainly on the right track. By adding quotes around the "0", you were comparing a variable of type int (Num02) with a string. Instead, use a literal 0 (without quotes):
if (Num02 == 0)
{
// print warning here
}
else
{
// do division and print result
}
I suggest extracting method for the user input (where we can check syntax - what if user put bla-bla-bla instead of number, extra condition(s) - we don't accept 0 as a second number etc.):
private static int ReadValue(string title,
Func<int, bool> extraCondition = null,
string extraConditionText = null) {
int result;
while (true) { // keep on asking until correct input provided
Console.WriteLine(title);
if (!int.TryParse(Console.ReadLine(), out result)) // syntax check
Console.WriteLine("Syntax error, please, input integer value");
else if (extraCondition != null && !extraCondition(result)) // extra check if any
Console.WriteLine(string.IsNullOrEmpty(extraConditionText)
? "Incorrect value"
: extraConditionText);
else
return result;
}
}
Then you can put
static void Main(string[] args) {
while (true) {
int Num01;
int Num02;
Console.WriteLine("What do you want to do?");
string Answer = Console.ReadLine().Trim();
if (string.Equals(Answer, "Quit", StringComparison.OrdinalIgnoreCase)) {
break;
}
else if (string.Equals(Answer, "Division", StringComparison.OrdinalIgnoreCase)) {
Num1 = ReadValue("Write number");
Num2 = ReadValue("Divided by?", x => x != 0, "Sorry you can't divide by 0");
Console.WriteLine($"{Num1} / {Num2} = {Num1 / Num2}");
}
else {
Console.WriteLine("Sorry, it's an incorrect option");
}
}
}
I have the following method and I want to separate the input part from the validation part, i.e. I want to read the input in one method (ReadInput) and to assert that the input value is of type double in another method (AssertIsDouble). How can I do that?
public static double ReadInput()
{
double number = 0;
while (true)
{
if (Double.TryParse(Console.ReadLine(), out number) && number > 0)
{
return number;
}
else
{
Console.WriteLine("Please, input a number greater than zero (0).");
}
}
}
I tried the following but it didn't work:
public static double ReadInput()
{
double number = 0;
while (true)
{
AssertIsDouble(Console.ReadLine());
}
}
private static double AssertIsDouble(string input)
{
double number = 0.0;
if (Double.TryParse(input, out number) && number > 0)
{
return number;
}
else
{
Console.WriteLine("Please, input a number greater than zero (0).");
}
}
I'd use an out parameter along with returning a bool from the Assert method.
Disclaimer: The code is untested but should work.
public static double ReadInput()
{
double number;
while (!AssertIsDouble(Console.ReadLine(), out number))
{
Console.WriteLine("Please, input a number greater than zero (0).");
}
return number;
}
public bool AssertIsDouble(string input, out double number)
{
return (Double.TryParse(input, out number) && number > 0);
}
Note that if I was you I'd also rename the methods as they are a bit unclear at the moment:
ReadInput: Read what input, as what?
AssertIsDouble: Not a bad name but it also does additional checks.
Also note the problem with your original code is this loop:
while (true)
{
AssertIsDouble(Console.ReadLine());
}
You never check/assign the return value from the method call and never set a condition to break out of the loop, thus you have an infinite loop.
What I commonly do to get strongly typed (non-string) input from the user is to have a separate method that takes in a prompt to display to the user, an error prompt to display if they enter an incorrect value, and the min/max values allowed for the input. This greatly simplifies the main code body:
private static double GetDoubleFromUser(
string prompt = "Please enter a number: ",
string errorPrompt = " - Error: input must be a number between {0} and {1}: ",
double minValue = double.MinValue, double maxValue = double.MaxValue)
{
double value;
// Write the prompt text and get input from user
if (prompt != null) Console.Write(prompt, minValue, maxValue);
while (!double.TryParse(Console.ReadLine(), out value)
|| value < minValue || value > maxValue)
{
// If input can't be converted to a double or is out of range, keep trying
if (errorPrompt != null) Console.Write(errorPrompt, minValue, maxValue);
}
// Return converted input value
return value;
}
Now, in your main body of code, you would just do something like:
double input = GetDoubleFromUser("Please input the amount: ",
"- input must be a number greater than zero: ", 0);
Console.WriteLine($"You entered: {input}");
And the method handles the rest: