Check if a value from scanf is a number?

by

http://www.cplusplus.com/reference/clibrary/cstdio/scanf/

On success, [scanf] returns the
number of items succesfully read. This
count can match the expected number of
readings or fewer, even zero, if a
matching failure happens. In the case
of an input failure before any data
could be successfully read, EOF is
returned.

So you could do something like this:

#include <stdio.h>

int main()
{
    int v;
    if (scanf("%d", &v) == 1) {
        printf("OK\n");
    } else {
        printf("Not an integer.\n");
    }
    return 0;
}

But it is suggest that you use fgets and strtol instead.

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