C :: Use Fgets And Sscanf To Read A Line Of Input

I'm new to C/C++. I am attemping to use fgets and sscanf to read a line of input, and confirm it is a positive number.My code works great, except for the case of a negative number. When I enter a negative number, my while loop seems to run infinitely, with stdin providng the same input over and over again.

Here's the code snippet:

Code:

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#define TEXT_LEN 64
void foo() {
char* inStr = (char*)malloc(sizeof(char)*TEXT_LEN);
memset(inStr, 0, TEXT_LEN);
}

[code]....