how to use scanf with integers or a char in c-CodePudding

Basically I have a simple loop that has a scanf

int main(void){
 int num, i;
  
 for(i=0; i<100; i  ){
 printf("enter a number or Q to quit");
 scanf("%d",&num);
 }
}

How can I use scanf with integers to keep the loop going and for the Chars 'Q' and 'q' to stop the loop by setting i to 100.

CodePudding user response：

Can't claim that this will work in all cases, but it seems to work for me.

int main() {
    int num, i;
    char q;

    for( i = 0; i < 100; i   ) {
        printf("enter a number or Q to quit: ");
        if( scanf("%d",&num) != 1 ) {
            scanf( " %c", &q );
            printf( "picked up %c\n", q );
        }
        printf("number %d\n", num );

    }
    return 0;
}

enter a number or Q to quit: 42
number 42
enter a number or Q to quit: 27
number 27
enter a number or Q to quit: q
picked up q
number 27

It's not very good code... You really should use fgets() and interpret whatever buffer load you get from the user.

CodePudding user response：

Here's my solution, similar to what Fe2O3 did:

#include <stdio.h> // IO
#include <stdbool.h> // Boolean values

int main(void)
{
    int value; // Integer value
    char ch; // Character value
    bool ended = false; // Loop ended state

    const unsigned int END_CH_LEN = 2; // Length of ending characters array
    char stop_ch[END_CH_LEN] = {'q', 'Q'}; // Ending characters

    for (int i = 0; i < 100; i  )
    {
        // Check loop ended state
        if (ended)
        {
            break;
        }

        // Print prompt
        printf("Enter a number or quitting character (q / Q): ");

        // Try to read integer, and check if the value is integer
        if (scanf("%d", &value) != 1)
        {
            // Read character
            scanf("%c", &ch);

            // Check for ending characters
            for (unsigned int i = 0; i < END_CH_LEN; i  )
            {
                // If match detected
                if (ch == stop_ch[i])
                {
                    // Exit loop
                    ended = true;
                    break;
                }
            }
        }
        else
        {
            // Print integer
            printf("Integer value: %d\n", value);
        }
    }

    return 0;
}

But still, as Fe2O3 previously mentioned, this code is not very scalable; the expected integer is fixed in size, and depending on the return value of scanf to detect non-numerical inputs may break things in the future. If possible, read everything into a string first, then use something like atoi for integer conversion, coupled with dynamic memory allocation for variable-sized strings if needed.