语句在for循环中打印两次（C中的简单计算器）

Question

我试图制作一个简单的计算器程序，但是我的打印和扫描语句在第一次循环后仍然打印两次。任何帮助将不胜感激。到目前为止，这是我的代码。

#include <stdio.h>

int main ()
{
    char(input) = 0;
    int(num1) = 0;
    int(num2) =0;

    int i;
    for(i=1; i!=0; i++)
    {
            printf("This program will perform the following math \n");
            printf("'+' :addtion of two integers\n");
            printf("'-': subtraction of two integers\n");
            printf("'*': multiplication of two integers\n");
            printf("'/' : division of two integers\n");
            printf("'%%' : modulus of two integers\n");
            printf("'q' or 'Q' : Quit the program\n");
            scanf("%c", &input);

            switch (input)
            {
                    case '+':
                            printf("Enter two integers:\n");
                            scanf ("%d%d", &num1, &num2);
                            printf("%d + %d = %d\n", num1, num2, num1 + num2);
                            break;
                    case '-':
                            printf("Enter two integers:\n");
                            scanf ("%d%d", &num1, &num2);
                            printf("%d - %d = %d\n", num1, num2, num1 - num2);
                            break;
                    case '*':
                            printf("Enter two integers:\n");
                            scanf ("%d%d", &num1, &num2);
                            printf("%d * %d = %d\n", num1, num2, num1*num2);
                            break;
                    case '/':
                            printf("Enter two integers:\n");
                            scanf ("%d%d", &num1, &num2);
                            if (num2 !=0)
                            {
                                    printf("%d / %d = %d\n", num1, num2, num1/num2);
                                    break;
                            }
                            else
                            {
                                    printf ("invalid input, denominator can not be 0");
                                    break;
                            }
                    case '%':
                             printf("Enter two integers:\n");
                            scanf ("%d%d", &num1, &num2);
                            if (num1 >= 0)
                            {
                                    printf("%d mod %d = %d\n", num1, num2, num1%num2);
                                    break;
                            }
                            else if (num2 >=0)
                            {
                                    printf("%d mod %d = %d\n", num1, num2, num1%num2);
                                    break;
                            }
                            else
                            {
                                    printf  ("invalid input, integers have to be positive");
                                    break;
                            }
                    case 'q':
                            printf("Goodbye\n");
                            i = -1;
                            break;
                    case 'Q':
                            printf("Goodbye\n");
                            i = -1;
                            break;
            }

    }

    return 0;
}

谢谢你们