how to add and subtract in C#?

Question

I am new to C# and I am trying to make a calculator. In Python(which I am more familiar with), You just import mathand then write out what it is you want to do with math.

But with C#, this is my code:

using system;


namespace Calculator
{
    class MainClass
    {
        public static void Main(string[] args)
        {
             divide(2,3);
        }
        public static void add(int num01, int num02)
        {
            Console.WriteLine("The result is " + num01+num02);
            Console.ReadKey();
        }
        public static void multiply(int num01, int num02)
        {
            Console.WriteLine("The result is " + num01 * num02);
            Console.ReadKey();
        }
        public static void divide(double num01, double num02)
        {
            Console.WriteLine("The result is " + num01 / num02);
            Console.ReadKey();
        }
        public static void subtract(int num01, int num02)
        {
            Console.WriteLine("The result is " + num01 - num02);
            Console.ReadKey();
        }
    }
}

And it firstly gives me 23 if I try to add, and throws a syntax error( Operator '-' cannot be applied to operands of type 'string' and 'int'.) if I try to subtract.

I'm only new to this language so I'm probably making some silly mistakes.

You're adding them as `string`. You need to get the values as `int` first. — Kyle, Jun 09 '17 at 16:23
`"The result is " + num01 - num02` is like `("The result is " + num01) - num02`; the number gets concatenated to the string first, and then the subtraction happens. (It associates left-to-right.) Use parentheses to change that. — Ry-, Jun 09 '17 at 16:24
Is there any language that computes `"Result = " + 4 -2"` as "Result = 2"? — Alexei Levenkov, Jun 09 '17 at 16:57
see: https://stackoverflow.com/questions/234217/is-it-possible-to-compile-and-execute-new-code-at-runtime-in-net — Greg, Jun 09 '17 at 17:37

score 6 · Answer 1 · answered Jun 09 '17 at 16:24

This mix-up comes from the confusion between two roles of +:

When it is used in an expression with strings, it denotes concatenation
When it is used in an expression with numeric types, it denotes addition

You can fix this problem by placing parentheses around your expressions.

However, a better approach is to use string formatting or string interpolation instead of concatenation, which lets you avoid this problem altogether:

Console.WriteLine("The result is {0}", num01 - num02); // Formatting

or

Console.WriteLine($"The result is {num01 - num02}"); // Interpolation

hack3rfx · Answer 2 · 2017-06-09T16:31:04.590

4

convert your final calculation to a string like so.

Console.WriteLine("The result is " + (num01 - num02).ToString());

Or just wrap in parenthesis

Console.WriteLine("The result is " + (num01 - num02));

edited Jun 09 '17 at 16:31

answered Jun 09 '17 at 16:24

hack3rfx

573
3
16

You don't have to use `.ToString()` – FCin Jun 09 '17 at 16:29

Majid Parvin · Answer 3 · 2017-06-09T19:30:03.423

just put in order your operations with ().

namespace Calculator
{
    class MainClass
    {
        public static void Main(string[] args)
        {
             divide(2, 3);
        }
        public static void add(int num01, int num02)
        {
            Console.WriteLine("The result is " + (num01 + num02));
            Console.ReadKey();
        }
        public static void multiply(int num01, int num02)
        {
            Console.WriteLine("The result is " + (num01 * num02));
            Console.ReadKey();
        }
        public static void divide(double num01, double num02)
        {
            Console.WriteLine("The result is " + (num01 / num02));
            Console.ReadKey();
        }
        public static void subtract(int num01, int num02)
        {
            Console.WriteLine("The result is " + (num01 - num02));
            Console.ReadKey();
        }
    }
}

score 0 · Answer 4 · answered Jun 09 '17 at 17:33

Order of Operations is really important in strongly typed languages like Java and C#. Like many already answered you are first adding the string to the first number and then trying to subtract from the string.

This is what your code is doing:

1. "The result is " + num01 - num02
2. "The result is (value of num01)" - num02
3. Error when trying to subtract

By changing it to this

Console.WriteLine("The result is " + (num01 - num02));

Your code executes like this:

1. "The result is " + (num01 - num02)
2. "The result is " + (difference of num01 and num02)
3. "The result is (difference of num01 and num02)"

Hope this helps

how to add and subtract in C#?

4 Answers4