Convert Hexadecimal String to Integer Without strtol or sscanf functions

Code

#include <stdio.h>
#include <stdint.h>
char hex[0xff]={0};
void setup(){
    for(int i=0,j='0';i<10;i++,j++) hex[j]=i;
    hex['a']=hex['A']=10;
    hex['b']=hex['B']=11;
    hex['c']=hex['C']=12;
    hex['d']=hex['D']=13;
    hex['e']=hex['E']=14;
    hex['f']=hex['F']=15;
}

uint16_t hex_to_uint(const char *str) {
    setup();
    uint16_t num=0;
    for(int i=0;str[i];i++){
        num*=16;
        num+=hex[str[i]];
    }
    return num;
}

int main() {
    char hex[10];
    scanf("%s", hex);

    printf("%u", hex_to_uint(hex));
    return 0;
}

Solving Approach