exercise 2-3 (the c programming language 2nd ed) hexadecimal constant strings to decimal

htoi.c

#include <stdio.h>

int getLength (char s[]) {
    int sz = 0;
    for (; s[sz] != '\0'; ++sz);
    return sz;
}

int pow (int c, int n) {
    int i = 0, v = 1;

    if (n == 0)
        return 1;

    for (; i < n; ++i)
        v *= c;

    return v;
}

int toInt (char c) {
    return c - '0';
}

char clower(int c) {
    if (c >= 'A' && c <= 'Z')
        return c + 'a' - 'A';

    return c;
}

int htoi (char cStr[]) {
    int ind = 0, m = 0, state = 1;
    int vInt = 0;

    if (cStr[ind] == '0') {
        if ( clower(cStr[ind + 1]) >= 'a' && clower(cStr[ind + 1]) <= 'w' ||
             clower(cStr[ind + 1]) == 'y' || clower(cStr[ind + 1]) == 'z' ) {
                return 0;
        }
        else if (clower(cStr[ind + 1]) == 'x') {
            for (ind = getLength(cStr) - 1; ind >= 2; --ind) {

                 if (clower(cStr[ind]) >= 'a' && clower(cStr[ind]) <= 'f') {
                    vInt += pow (16, m) * (clower(cStr[ind]) - 102 + 15);
                    ++m;
                    }
                 else if (cStr[ind] >= '0' && cStr[ind] <= '9') {
                    vInt += pow (16, m) * toInt (cStr[ind]);
                    ++m;
                    }
            }

            state = 0;
        }


    }

    if (state) {
     for (ind = getLength(cStr); ind >= 0; --ind) {

            if (clower(cStr[ind]) >= 'a' && clower(cStr[ind]) <= 'f') {
                vInt += pow (16, m) * (clower(cStr[ind]) - 102 + 15);
                ++m;
            }
            else if (cStr[ind] >= '0' && cStr[ind] <= '9') {
                vInt += pow (16, m) * toInt (cStr[ind]);
                ++m;
            }
        }

    }

     return vInt;

}

int main ()
{
    printf ("\n%d", htoi("0x1a"));

    return 0;
}