Using strtol to validate integer input in ANSI C

Question

I am new to programming and to C in general and am currently studying it at university. This is for an assignment so I would like to avoid direct answers but are more after

Answer 1

The function strtol returns long int, which is a signed value. I suggest that you use another variable (entry_num), which you could test for <0, thus detecting negative numbers.

I would also suggest that regex could test string input for digits and valid input, or you could use strtok and anything but digits as the delimiter ;-) Or you could scan the input string using validation, something like:

int validate_input ( char* input )
{
    char *p = input;
    if( !input ) return 0;
    for( p=input; *p && (isdigit(*p) || iswhite(*p)); ++p )
    {
    }
    if( *p ) return 0;
    return 1;
}