Convert a string to an integer in C.

str-to-int.c

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

int str_to_int(char *str)
{
    int base = 10;
    char *end_ptr;
    errno = 0;

    int value = (int)strtol(str, &end_ptr, base);

    if (errno != 0 || str == end_ptr) {
        fprintf(stderr, "\nERROR: Couldn't convert \"%s\" to an integer.\n\n", str);
        exit(EXIT_FAILURE);
    }

    return value;
}