Hex string to integer

htoi.c

#include <stdio.h>

long hexToInt(char hexString[]) {
    long result = 0;

    for (int i = 0; hexString[i] != '\0'; i++) {
        if ((hexString[i] == '0' && hexString[i + 1] == 'x') || hexString[i] == 'x') {
            continue;
        }

        int value = 0;

        if (hexString[i] >= '0' && hexString[i] <= '9') {
            value = hexString[i] - '0';
        } else if (hexString[i] >= 'a' && hexString[i] <= 'z') {
            value = (hexString[i] - 'a') + 10;
        } else if (hexString[i] >= 'A' && hexString[i] <= 'Z') {
            value = (hexString[i] - 'A') + 10;
        }

        result = result * 16 + value; // multiply by 16 for correct digit shifting because we're iterating left to right.
    }

    return result;
}

int main() {
    long result = hexToInt("0xabcdef");

    printf("%ld\n", result);
}