119. Convert Hexadecimal String to Integer Without strtol or sscanf functions

#include <stdio.h>
#include <stdint.h>

uint16_t hex_to_uint(const char *str) {
    uint16_t p=1;
    uint16_t sum=0;
    uint16_t length=0;
    while(str[length]!='\0'){
        length++;
    }
    for(int i=length-1;i>=0;i--){
        if(str[i]>='A'&&str[i]<='F'){
            sum+=(str[i]-55)*p;
        }
        else if(str[i]>='a' && str[i]<='f'){
            sum+=(str[i]-87)*p;
        }
        else{
            sum+=(str[i]-'0')*p;
        }
        p*=16;
    }
    return sum;
}

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

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