C-while循环挂在条件上

Question

I'm a newbie learning code so this might be pretty simple but I can't understand what is happening.

When I try to run the following code it seems to hang on the while loop condition and doesn't execute any code after that. Is the != operator not suited for this?

I also tried a do {} while and everything ran fine but as soon as I set the operator to 'E' , again the condition seems to hang there and doesn't get out of the loop.

#include <stdio.h>

int main(void) {
    float n, content;
    char operator;

    n = content = 0;
    operator = 'a';

    printf("Begin Calculations:\n");

    while (operator != 'E');
    {
        scanf("%f %c", &n, &operator);

        switch (operator) {
        case 's':
        case 'S':
            content = n;
            printf("= %f\n", content);
            break;

        case '+':
            content = content + n;
            printf("= %f\n", content);
            break;

        case '-':
            content = content - n;
            printf("= %f\n", content);
            break;

        case '*':
            content = content * n;
            printf("= %f\n", content);
            break;

        case '/':
            content = content / n;
            printf("= %f\n", content);
            break;

        case 'e':
        case 'E':
            printf("End of calculations\n");
            operator == 'E';
            break;

        default:
            printf("Invalid input\n");
            break;
        }
    }
    return 0;
}

Answer 1

Remove the semicolon at the end of the while statement:

while(operator != 'E')
{

The semicolon ends the body of the while statement, in other words it behaves as if you would write this:

while(operator != 'E')
{
}

causing an infinite loop.

Answer 2

1. You need to remove the semi-colon at the end of while
2. You need to take into account both cases

So change

while(operator != 'E');

to

while(operator != 'E' && operator != 'e')

Answer 3

You have a classic bug in your while loop:

while (operator != 'E');
{

The ; after the condition is parsed as en empty statement, hence your while runs forever if operator is different from 'E' .

Using the classic Kernighan and Ritchie brace style makes this kind of bug obvious and much less likely to occur:

while (operator != 'E') {

Also note that you should exit your loop from the switch statement instead of testing for E in the while condition, this would allow for both e and E to be handled correctly (your statement operator == 'E'; is a no op, it should be written operator = 'E'; . Also check the return value of scanf to avoid looping endlessly at end of file.

Here is an improved version:

#include <stdio.h>

int main(void) {
    float n, content;
    char operator;
    int active = 1;

    n = content = 0;

    printf("Begin Calculations:\n");

    while (active && scanf("%f %c", &n, &operator) == 2) {
        switch (operator) {
        case 's':
        case 'S':
            content = n;
            printf("= %f\n", content);
            break;

        case '+':
            content = content + n;
            printf("= %f\n", content);
            break;

        case '-':
            content = content - n;
            printf("= %f\n", content);
            break;

        case '*':
            content = content * n;
            printf("= %f\n", content);
            break;

        case '/':
            content = content / n;
            printf("= %f\n", content);
            break;

        case 'e':
        case 'E':
            printf("End of calculations\n");
            active = 0;
            break;

        default:
            printf("Invalid input\n");
            break;
        }
    }
    return 0;
}

Answer 4

while(operator != 'E');

The correct syntax is while (...) { ... } without semicolon or do { ... } while (...); with.

printf("End of calculations\n");
operator == 'E';

The assignment operator is a single = . Change == into = and it should be fine.

Answer 5

您需要从while循环中删除分号，因为分号意味着语句结束，因此您的程序不会进一步执行

Answer 6

couple of things. 1- operator is a reserve word, you should change the variable name 2- (semicolon ;) after while()

Check update code:

        #include <stdio.h>

        int main(void)
        {
          float n, content;
          char operator1;

          n = content = 0;
          operator1 = 'a';

          printf("Begin Calculations:\n");

          while(operator1 != 'E')
          {
            scanf("%c", &operator1);

            switch(operator1)
            {
              case 's':
              case 'S':
            content = n;
            printf("= %f\n", content);
            break;

              case '+':
            content = content + n;
            printf("= %f\n", content);
            break;

              case '-':
            content = content - n;
            printf("= %f\n", content);
            break;

              case '*':
            content = content * n;
            printf("= %f\n", content);
            break;

              case '/':
            content = content / n;
            printf("= %f\n", content);
            break;

              case 'e':
              case 'E':
            printf("End of calculations\n");
            operator1 = 'E';
            break;

              default:
            printf("Invalid input\n");
            break;
            }
          }
          return 0;
        }