Thread: Checking that a string contain only numeric characters in C...

Well...

• You don't need a nested loop.
• You should compare ANS[i] with 'n', not "n".
• Use !isdigit(ANS[i]).
• Think carefully about your use of ||. Should && be used instead?
• Do not use fflush(stdin). Rough alternatives include just reading and discarding chars until you encounter a '\n' or EOF.
• Do not use gets. Rough alternatives include fgets.
• Your indentation could be improved.

You can't compare strings with ==. You need something like strcmp. Or you could do what you're doing later on there, and compare individual characters. I'm not sure why you're going back and forth. You shouldn't use gets either. You should just make a function that checks your input and returns something if it's OK, and something else if it's not.

Code:

int checkinput( char input[], int len )
{
    if input[0] is n
        return OK (optionally, return something else saying they wanted to quit)
    else 
        for each character in
            if you found a non-number
                return NOT OK
    else
        you reached the end and just had numbers so return OK
}

Quzah.