isdigit woes

[kryonik]

Im trying to use isdigit to invoke an error if a string has anything other than a digit in it and having no luck. My old code line will kick out something that starts with a non integer value, ex. e356, it will error but not error out with 3e56. I tried to utilize isdigit in place but I cant seem to get the syntax right. Am I even barking up the right tree trying to invoke isdigit for this kind of task?

#include <stdio.h>
#include <ctype.h>
// THIS IS BROKEN!!!!
#define MAXLINE 40

int main(void)
{
int error, n ;
char line[MAXLINE];
do {
	printf("Input a positive integer:  ");
	fgets(line, MAXLINE, stdin);
	//error = sscanf(line, "%d", &n) !=1 || n <= 0;// Old code
	error = sscanf(line, "%d", &n) !=isdigit(n); //DOES NOT WORK
	if(error)
	printf("\nERROR: Do it again.\n");
	}while(error);	
	
printf("your line was:  %s",line);

return 0;
}

[itsme86]

What the hell is that line of code? isdigit() expects a single character, but you're passing it a pre-processed integer. Try something like this instead:

{
  int i;

  for(i = 0;line[i] && line[i] != '\n';++i)
    if(!isdigit(line[i]))
      printf("OOOO! %c is not a digit!\n", line[i]);
}

[quzah]

To be technically accurate, isdigit does in fact expect an int. However, the value is supposed to be that of a valid char, or EOF. So the call is valid C, it just won't do what they expect it to.

Quzah.

[itsme86]

Notice that I said 'character' and not 'char'. I appreciate the clarification though.