How to parse and validate a number in C

main.c

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

int main(int argc, char* argv[]) {
    char str[100] = "13333333333333";
    char* endPtr;
    long long x = strtoll(str, &endPtr, 10);
    if (str == endPtr) {
        printf("Number could not be parsed!\n");
        return 1;
    }
    if (errno == ERANGE) {
        printf("Number is too big to store in the variable!\n");
        return 1;
    }
    printf("%lld\n", x);
    return 0;
}