Using isalpha()

I have tried & tried & tried to figure out what's wrong with my code but I can't . I's supposed to give an error if the user enters anything else but an integer . So something like : 34j , should be comming up as an error.
Thanks for any help you can give !

Code:

#include <stdlib.h>
#include <stdio.h>
#include <ctype.h>
#include <string.h>

#define MAXLINE 25  

int check(char *line);
char line[MAXLINE];
int error,n,digit,flag;
int i = 0;
int flag = 0;


void main(){ 
	
	do{
		printf("Input a posetive integer: ");
		if (fgets(line,MAXLINE,stdin) != NULL){
		 digit = check(&line);
		 error = ((sscanf(line,"/t%d/t",&n) != 1 || n <= 0) && (digit == 1));  
		}
		if (error)
			printf("\nERROR: Do it again .\n");
		else 
			printf("There was no error!");
	}while (error);
   
}

int check(char *line){ 
	while((i < MAXLINE) && (flag == 0)){
		if (isalpha((int)line[i]))
	      flag = 1;
	    ++i;
	}
	if (flag = 0)
		return 0;
	else
		return 1;
}

Common problem, a swap of the assignment and the testing operator...

Code:

  	if (flag = 0)
 		return 0;
 	else
 		return 1;

notice you're assigning flag to 0, not testing if it EQUALS zero

Simple mistake that we all make every now and then, just change the = to a == and you'll be set to go

Thanks! Ive done that , but while debugging after i've entered the values 5t , t5, t, 5
the 5 still gives an error while it shouldn't ??

You're using a lot of global variables in this program that are causing you more of a headache then anything, heh.

What's happening is

1) not resetting the i to 0
2) not resetting the flag to 0
3) you should only test (i < strlen(line)) in order to only test the inputted data.

Code:

 int check(char *line){ 
 	i=0;
 	flag=0;
 	while((i < strlen(line)) && (flag == 0))
 	{
 		if (isalpha((int)line[i]))
 		  flag = 1;
 		++i;
 	}
 	if (flag == 0)
 		return 0;
 	else
 		return 1;
 }

Thank you soooo much it works now, it was such a pain in the butt this program lol . Thanks again!