How to scanf only integer?

Question

I want the code to run until the user enters an integer value.

The code works for char and char arrays.

I have done the following:

#include <stdio.h>

int main()
{
    int n;
    printf("Please enter an integer: ");
    while(scanf("%d",&n) != 1)
    {
        printf("Please enter an integer: ");
        while(getchar() != '\n');
    }
    printf("You entered: %d\n",n);
    return 0;
}

The problem is if the user inputs a float value scanf will accept it.

Please enter an integer: abcd
Please enter an integer: a
Please enter an integer: 5.9
You entered: 5

How can that be avoided?

Answer 1

1. You take scanf().
2. You throw it in the bin.
3. You use fgets() to get an entire line.
4. You use strtol() to parse the line as an integer, checking if it consumed the entire line.

char *end;
char buf[LINE_MAX];

do {
     if (!fgets(buf, sizeof buf, stdin))
        break;

     // remove \n
     buf[strlen(buf) - 1] = 0;

     int n = strtol(buf, &end, 10);
} while (end != buf + strlen(buf));

Answer 2

Use fgets and strtol,

A pointer to the first character following the integer representation in s is stored in the object pointed by p, if *p is different to \n then you have a bad input.

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

int main(void) 
{
    char *p, s[100];
    long n;

    while (fgets(s, sizeof(s), stdin)) {
        n = strtol(s, &p, 10);
        if (p == s || *p != '\n') {
            printf("Please enter an integer: ");
        } else break;
    }
    printf("You entered: %ld\n", n);
    return 0;
}