C ++，构造一个读取两个实数和一个字符的程序

Question

I am trying to write a program that is able to read two real numbers followed by a character which is inputted by the user. Then the program will evaluate the two numbers by the character. The character can be any of the ones that I have listed below:
1. + (addition)
2. - (subtraction)
3. * (multiplication)
4. / (division)
5. % (remainder)

Below I have posted the code that I have written just to check if the values printed out are correct:

#include<stdio.h>

int main(){
    float a,b,add,subtract,division,multiply,remainder;
    char op;

    printf("Enter two real numbers followed by one these characters:+, -, *, /, or % : ");
    scanf("%f%f %c",&a,&b,&op);
    printf("%.1f %c %.1f\n",a,op,b);

    if (op=='+'){
        add =  a + b;
        printf("%f",add);
    }
    else if (op=='-'){
        subtract=a-b;
        printf("%f",subtract);
    }
    else if (op=='/'){
        division=a/b;
        printf("%f",division);
    }
    else if (op=='*'){
        multiply =a*b;
        printf("%f",multiply);
    }
    else if (op=='%'){
        remainder=a%b;
        printf("%f",remainder);
    }
    else{
        printf("invalid symbol");
    }
    return 0; 
}

Can anyone tell me why I am getting a run time error?

Answer 1

NOTE: The OP significantly altered the initial question after it had been answered, which is what this post was focusing on, so the answer below may look completely off-target by now.

---

If anyone can explain why I see different values that would be greatly appreciated.

There're multiple issues with your code.

1. The command-line input for your program has to be properly converted to float types, but it converts them to int s. Your scanf should use "%f %f %c" instead to take real numbers instead of integer numbers;
2. IIRC from your previous picture, your actual inputs to the program looked like this: 2 2 + , but your scanf says "%d%d %c" (notice the missing space in your format string vs your extra space in your input)
3. Your printf function call needs the arguments swapped to say printf("%f %c %f",a, op, b); (notice the format string using "%f" and the inversion of op and b variables)

The 1st point is based on the printed text for the user, requesting "real" numbers.

The 2nd and 3rd points are the culprits, because when you enter 2 2 + on the prompt, your variables look are a = 2 , b = 2 , and op = 43 , which is the numeric value of the '+' character.

When you then print it, you end up interpreting the '+' char as if it were an integer and you get 43 instead.

A fixed version of your program is below:

#include<stdio.h>

int main(){
    float a, b, result;
    char op;
    printf("%s", "Enter two real numbers followed an operator (+, -, *, /, %): ");
    scanf("%f %f %c", &a, &b, &op);

    switch(op) {
        case '+':
            result = a + b;
            break;
        case '-':
            result = a - b;
            break;
        case '*':
            result = a * b;
            break;
        case '/':
            /* make sure b != 0 */
            result = a / b;
            break;
        case '%':
            /* make sure b != 0 */
            /* we type-cast to int because modulus is not defined for floats */
            result = (float)((int)a % (int)b);
            break;
        default:
            printf("%s\n", "Unknown operation");
            break;
    }

    printf("%f %c %f = %f",a, op, b, result);
    return 0;
}

Its usage and output:

➜  /tmp ./test
Enter two real numbers followed an operator (+, -, *, /, %): 5 5 +
5.000000 + 5.000000 = 10.000000
➜  /tmp ./test
Enter two real numbers followed an operator (+, -, *, /, %): 5 5 *
5.000000 * 5.000000 = 25.000000%
➜  /tmp ./test
Enter two real numbers followed an operator (+, -, *, /, %): 5 5 /
5.000000 / 5.000000 = 1.000000%
➜  /tmp ./test
Enter two real numbers followed an operator (+, -, *, /, %): 10 5 %
10.000000 % 5.000000 = 0.000000%
➜  /tmp ./test
Enter two real numbers followed an operator (+, -, *, /, %): 5 10 %
5.000000 % 10.000000 = 5.000000%
➜  /tmp ./test
Enter two real numbers followed an operator (+, -, *, /, %): 8 5 -
8.000000 - 5.000000 = 3.000000

Answer 2

The problem is in the way you're printing it. You're trying to print a number as a char and a char as a number:

printf("%d %c %d",a,b,op);

I think you meant:

printf("%d %d %c",a,b,op);

So it was just printing the ASCII value of b, which will give you a funny character as you have there.