Convert Hexadecimal String to Integer Without strtol or sscanf functions

Question

Problem: Convert Hexadecimal String to Integer Without strtol or sscanf functions. Solve this hands-on electronics task on EWskills.

Accepted Answer

#include 
#include 

// Convert a single hex char to its integer value
uint8_t hex_char_to_val(char c) {
    if (c >= '0' && c <= '9') return c - '0';
    else if (c >= 'A' && c <= 'F') return c - 'A' + 10;
    else if (c >= 'a' && c <= 'f') return c - 'a' + 10;
    else return 0; // Invalid character, could return error
}

// Convert hex string to unsigned integer
uint16_t hex_to_uint(const char *str) {
    uint16_t result = 0;
    for (int i = 0; str[i] != '\0'; i++) {
        result <<= 4; // shift by 4 bits (hex digit)
        result |= hex_char_to_val(str[i]);
    }
    return result;
}

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

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

Why This is Important in Firmware?

Used in CLI tools, bootloaders, debug utilities
Avoids linking large libraries (stdlib, sscanf)
Needed in parsing hex configuration values or memory dump input

Logic Summary

For each character in hex string:
- Convert using manual mapping
- Left shift result by 4 bits
- OR in the new value

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