C#: operator '-' cannot be applied to operands of type 'string' and 'int' error

Question

So I have almost completed my program but I keep getting this error for the subtraction operator. I have searched throughout my book and the internet but can find no fix for this. Is anybody able to tell me what is wrong with this code?

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace ConsoleApplication14
{
class Program
{
    static void Main(string[] args)
    {
        int int1;
        int int2;
        char oper;

        Console.Write("Enter first integer: ");
        int1 = Convert.ToInt32(Console.ReadLine());

        Console.Write("Enter operator (+,-,*, / or %)");
        oper = Convert.ToChar(Console.ReadLine());

        Console.Write("Enter first integer: ");
        int2 = Convert.ToInt32(Console.ReadLine());

        if(oper == '+')
            Console.Write("Answer is: " + int1 + int2);

        if (oper == '-')
            Console.Write("Answer is: " + int1 - int2);

        if(oper == '*')
            Console.Write("Answer is: " + int1 * int2);

        if(oper == '/')
            Console.Write("Answer is: " + int1 / int2);

        if(oper == '%')
            Console.Write("Answer is: " + int1 % int2);

        Console.ReadKey();
    }
}

}

try wrapping inside (): Console.Write("Answer is: " + (int1 - int2)); — Khanh TO
– Khanh TO, Commented Jan 27, 2014 at 10:13
That worked! Thank you. Why does the '-' operator require () unlike the others? — Chris Buege
– Chris Buege, Commented Jan 27, 2014 at 10:15
A word of advice, Use Switch/if..else..if in stead of so many if. — Sumit Gupta
– Sumit Gupta, Commented Jan 27, 2014 at 10:15
It is not the operator. It is the context. Actually, you should enclose all your results in parenthesis if you wish to have the desired result. For example "Answer is: "+int1+int2 will return "Answer is: 32", if int1 is 3 and int2 is 2 — ThunderGr
– ThunderGr, Commented Jan 27, 2014 at 10:17

Plue · Accepted Answer · 2014-01-27 10:24:27Z

6

Console.Write("Answer is: " + int1 - int2);

You are first concatenating a string with int1, resulting in a string. Then you try to substract this string with int2.

Try this :

Console.Write("Answer is: " + (int1 - int2));

Thus you will first evaluate (int1 - int2) and then concatenate it.

By the way, you will also have to do it for the '+' operator. Else you will concatenate int2 to int1. For the other operators, it should work thanks to the precedence on '+'.

edited Jan 27, 2014 at 10:24

answered Jan 27, 2014 at 10:14

Plue

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2 Comments

Rawling Over a year ago

... for very operator - not so. *, / and % have higher precedence than +. Whether he should do it for every operator is another matter :)

Plue Over a year ago

Thanks, I was not sure precedence would work the same with different types

Selman Genç · Accepted Answer · 2014-01-27 10:15:03Z

3

Console.Write("Answer is: {0} ",int1 - int2);

answered Jan 27, 2014 at 10:15

Selman Genç

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Comments

Roy Dictus · Accepted Answer · 2014-01-27 10:14:55Z

1

Use a comma to separate parameters in Console.Write and use a placeholder {0}, like so:

Console.Write("Answer is: {0}", int1 - int2);

This does not confuse the compiler.

answered Jan 27, 2014 at 10:14

Roy Dictus

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Comments

Sameer · Accepted Answer · 2014-01-27 10:15:03Z

1

    if(oper == '+')
        Console.Write("Answer is: " + (int1 + int2));

    if (oper == '-')
        Console.Write("Answer is: " + (int1 - int2));

    if(oper == '*')
        Console.Write("Answer is: " + (int1 * int2);

    if(oper == '/')
        Console.Write("Answer is: " + (int1 / int2));

    if(oper == '%')
        Console.Write("Answer is: " + (int1 % int2));

answered Jan 27, 2014 at 10:15

Sameer

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