#include <stdio.h>
int  myatoi(char achar);
unsigned char BitShift(unsigned char x);

int main()
{
    unsigned char val;
    unsigned char par;

    val = myatoi('a');
    printf("Val: %un", val);
    par = BitShift(val);
    printf("Par: %un", par);
}

unsigned char BitShift(unsigned char x)
 {
     x ^= x >> 4;
     x ^= x >> 2;
     x ^= x >> 1;
     return (x & 0x1);
 }

 int  myatoi(char achar)
{
    int value;

    switch(achar)
    {
    case '0':
        value = 0;
        break;
    case '1':
        value = 1;
        break;
    case '2':
        value = 2;
        break;
    case '3':
        value = 3;
        break;
    case '4':
        value = 4;
        break;
    case '5':
        value = 5;
        break;
    case '6':
        value = 6;
        break;
    case '7':
        value = 7;
        break;
    case '8':
        value = 8;
        break;
    case '9':
        value = 9;
        break;
    case 'a':
    case 'A':
        value = 10;
        break;
    case 'b':
    case 'B':
        value = 11;
        break;
    case 'c':
    case 'C':
        value = 12;
        break;
    case 'd':
    case 'D':
        value = 13;
        break;
    case 'e':
    case 'E':
        value = 14;
        break;
    case 'f':
    case 'F':
        value = 15;
        break;
    default:
        value = 0;
    } // end switch

    return value;

}

Val = 10
x ^= x >> 4;  gives x = 10
x ^= x >> 2;  gives x = 8
x ^= x >> 1;  gives x = 12
Par = 0