做……在 C 中终止程序

Question

I am using do...while as a loop control in C language. I need to terminate the program when the user enters "99", else the user should guess the number to terminate the program, until then the program will run. Here is the code. I don't have any compiler error, but instead it prints the number 0 to the number the users entered.

#include <stdio.h>
#include <stdbool.h>
int main(void)
{
    int num = 0;

    do {
        scanf("Enter the magic number to terminate this program: %d\n", &num);

        printf("You entered : %d\n", num);

        num++;

    } while (num != 100);

    printf("\nThe magic number is correct and the program is terminated:");

    return 0;
}

Any help is appreciated.

Answer 1

scanf is not like Python's input , for example. It requires the exact input that you specify in the format string. In your particular case, you are expecting the users to enter "Enter the magic number to terminate this program: ", followed by a number.

One way to check this is to use the return value, which tells you the number of matched arguments:

k = scanf("...\n", &num);
printf("scanf managed to get %d inputs\n", k);

The solution is to split the input and output portions:

printf("Enter the magic number to terminate this program: ");
scanf("%d", &num);

scanf will automatically filter out whitespace between inputs, including the newlines that the user enters. You can also consume those explicitly with either "%d\n" or equivalently "%d " . However, you shouldn't do that. scanf treats any whitespace characters as "any number of whitespace", and will block until it receives the next non-whitespace character. It will also cause a problem if your stream ends without a trailing newline.