C程序基本计算器

Question

#include<stdio.h>
int main()
{
    int a,b;
    char op;
    scanf("%d",&a);
    scanf("%c",&op);
    scanf("%d",&b);
    int w,x;
    w=a+b;
    x=a-b;

    switch(op)
    {
        case'+':
        {
            printf("%d",w);
            break;
        }
        case'-':
        {
            printf("%d",x);
            break;
        }
        default:
        {
            printf("Invalid");
            break;
        }
    }
    return 0;
}

Every time I enter the second input – the character(+ or -) – it directly goes to invalid in the switch case. What am I doing wrong here?

Answer 1

Your scanf sequence isn't doing what you think it is. Print out the value of op before the switch and you'll see the problem.

Answer 2

Your program works just fine. Your problem is with the input: use 123+456 instead of pressing enter between the decimal and the operator.

Here is an example of your program:

$ ./basic 
456-123
333$ 

I suggest adding \\n to each printf() format string to eliminate the prompt displaying in the same line.