why does the do while skip scanf when none digit character is inputted

In c I have this snippet

    int n=0; 
    do {
        printf("random text\n");
        scanf("%d", &n); 
    } while ( n < 1 || n > 10);

when the user inputs anything other than a number the loop spams the printf without waiting for user input

why does this happen and how do I fix this

by packet_sniffer in StackOverflow on June 05, 2022.

Answer

You need to skip the current content of the buffer if it does not contain a valid number. For example

int n=0; 
do {
    printf("random text\n");
    if ( scanf("%d", &n) == 0 )
    {
        scanf( "%*[^\n]" );
    }    
} while ( n < 1 || n > 10);

Pay attention to that this prompt

    printf("random text\n");

is confusing when you expect from the user to enter a number.

In general you should also add a check for EOF. For example

int n=0; 
do {
    n = 0;
    printf("random text\n");

    int result = scanf("%d", &n);

    if ( result == 0 )
    {
        scanf( "%*[^\n]" );
    }
    else if ( result == EOF )
    {
        break;
    }  
} while ( n < 1 || n > 10);

if ( n == 0 ) exit( 1 );
//...

by Vlad from Moscow on June 05, 2022.