Bring to your attention solution, that based on logical operations and shifts.
It use only 3 bytes memory :-) (2 bytes when use h to storage result (need more checks)).

If used GCC bit count can be replacement to __builtin_popcount and 1-byte instruction in SSE4.





scanf("%c%c\n",&h,&v);
r = 0xFF;
switch(h){
    case 'a': r &= 0x17;break;
    case 'b': r &= 0x3F;break;
    case 'g': r &= 0xFC;break;
    case 'h': r &= 0xE8;break;
}
switch(v){
    case '1': r &= 0x71;break;
    case '2': r &= 0xF3;break;
    case '7': r &= 0xCF;break;
    case '8': r &= 0x8E;break;
}
r -= ((r >> 1) & 0x55);
r = (r & 0x33) + ((r >> 2) & 0x33);
r = r + (r >> 4) & 0x0F;
printf("%d\n", r);