Checking user input

Hi , Im having some trouble to get this program to work.
The user is supposed to enter an integer & then a filename.
The program should check whether the integer is just that , only an integer & doesn't contain any characters.

Thanks for any help

Code:

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


void get_info(char *filename,int *n_ptr);
FILE *cfopen(char *filename,char *mode);
FILE *gfopen(char *filename,char *mode);
void prn_rand(FILE *ofp, int n);
int check(int *n_ptr);

FILE *fp;
int digit,flag,i,n;

void main(){
  char file[25];
  FILE   *ofp;
  get_info(file,&n);
  ofp = cfopen(file,"w");
  
  for(i = 1;i <= n;++i){
	  fprintf(ofp,"%12d", rand());
	  if (i % 6 == 0 || i == n)
		  fprintf(ofp,"\n");
  }
  prn_rand(ofp, n);
}
void get_info(char *filename,int *n_ptr){
	do{
	printf("\n%s\n\n%s",
		"This program creates a file of random numbers.",
		"How many random numbers would you like? ");
	     if(fgets((char)n_ptr,sizeof(n_ptr),stdin) != NULL);
              digit = check(n_ptr);

	     if (digit == 1)
		      printf("ERROR:type in an integer again.");
	} while (digit == 1);
		
	printf("\nIn what file would you like them? ");
	scanf("%s",filename);
}
FILE *cfopen(char *filename,char *mode){
	char reply[2];
	if (strcmp(mode, "w") == 0
		&& (fp = fopen(filename,"r")) != NULL){
		  fclose(fp);
	      printf("\nFile exists.Overwrite it?");
		  scanf("%1s",reply);
		  if (*reply != 'y' && *reply != 'Y'){
			  printf("\nBye!\n\n");
			  exit(1);
		  }
	}
	fp = gfopen(filename,mode);
	return fp;
}
FILE *gfopen(char *filename,char *mode){
   if ((fp = fopen(filename,mode)) == NULL) {
	   fprintf(stderr, "Cannot open %s -bye!\n",filename);
	   exit(1);
   }
   return fp;
}

void prn_rand(FILE *ofp, int n)
{
   printf("\nHello from prn_rand()\n\n");
}

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

Im guessing the problem is either somewhere with useing (or not useing the address operator) , & the pointers.??
As I have some trouble understanding these concepts ...

I haven't read the whole thing yet, but this is definitely wrong:

Code:

	     if(fgets((char)n_ptr,sizeof(n_ptr),stdin) != NULL);

What you have to do is something like:

Code:

fgets(some_string_array, sizeof(some_string_array), stdin);
*n_ptr = atoi(some_string_array);

EDIT: Reading a bit further, you want to call your check() function on the some_string_array. Then your check() function could look like this:

Code:

int check(char *str)
{
  while(*str)
  {
    if(!isdigit(*str))
      return 1;
    str++;
  }

  return 0;
}

Thanks for the help
I've changed my code a bit , but im still getting debug errors.

Code:

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


void get_info(char *filename,char *integer);
FILE *cfopen(char *filename,char *mode);
FILE *gfopen(char *filename,char *mode);
void prn_rand(FILE *ofp, int n);
int check(char *integer);

FILE *fp;
int digit,flag,i,n;

void main(){
  char file[25];
  char integer[3];
  FILE   *ofp;
  get_info(file,&integer);
  ofp = cfopen(file,"w");
  
  for(i = 1;i <= n;++i){
	  fprintf(ofp,"%12d", rand());
	  if (i % 6 == 0 || i == n)
		  fprintf(ofp,"\n");
  }
  prn_rand(ofp, n);
}
void get_info(char *filename,char *integer){
	do{
	printf("\n%s\n\n%s",
		"This program creates a file of random numbers.",
		"How many random numbers would you like? ");
	     if(fgets(integer,sizeof(integer),stdin) != NULL);
              digit = check(integer);
	     if (digit == 1)
		      printf("ERROR:type in an integer again.");
	} while (digit == 1);
		
	printf("\nIn what file would you like them? ");
	scanf("%s",filename);
}
FILE *cfopen(char *filename,char *mode){
	char reply[2];
	if (strcmp(mode, "w") == 0
		&& (fp = fopen(filename,"r")) != NULL){
		  fclose(fp);
	      printf("\nFile exists.Overwrite it?");
		  scanf("%1s",reply);
		  if (*reply != 'y' && *reply != 'Y'){
			  printf("\nBye!\n\n");
			  exit(1);
		  }
	}
	fp = gfopen(filename,mode);
	return fp;
}
FILE *gfopen(char *filename,char *mode){
   if ((fp = fopen(filename,mode)) == NULL) {
	   fprintf(stderr, "Cannot open %s -bye!\n",filename);
	   exit(1);
   }
   return fp;
}

void prn_rand(FILE *ofp, int n)
{
   printf("\nHello from prn_rand()\n\n");
}

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

what errors are you getting?

Your get_info() function is still not correct. Stuff that's wrong:

- You're passing &integer to the get_info() from main(). You should just be passing integer.
- The second arg to fgets() in in your get_info() is sizeof(integer). It should be 3. If you do sizeof() on a pointer you'll only get the size of the pointer (generally 4 bytes). This is a common mistake people make.

I haven't looked at the rest yet, but you should fix those couple of things and go from there.

cool , it works now ! thanks alot itsme it was very nice of you to help me