Example: Hexadecimal to Binary Converter with Lookup Array in C

// Hexadecimal to Binary Converter with Lookup Array
#include <stdio.h>
#include <string.h> // Required for strlen()
#include <ctype.h>  // Required for toupper()

// Lookup array for 4-bit binary equivalents of hex digits (0-F)
const char* hex_to_bin_map[] = {
    "0000", "0001", "0010", "0011", // 0, 1, 2, 3
    "0100", "0101", "0110", "0111", // 4, 5, 6, 7
    "1000", "1001", "1010", "1011", // 8, 9, A, B
    "1100", "1101", "1110", "1111"  // C, D, E, F
};

// Function to get the integer value of a hexadecimal character
int get_hex_value(char c) {
    if (c >= '0' && c <= '9') {
        return c - '0';
    } else if (c >= 'A' && c <= 'F') { // Handle uppercase A-F
        return c - 'A' + 10;
    } else if (c >= 'a' && c <= 'f') { // Handle lowercase a-f
        return c - 'a' + 10;
    } else {
        return -1; // Invalid hex character
    }
}

int main() {
    char hexNum[20];
    int i = 0;

    // Step 1: Prompt user for input
    printf("Enter a hexadecimal number: ");
    scanf("%s", hexNum);

    printf("Binary equivalent: ");

    // Step 2: Iterate through each character of the hexadecimal string
    while (hexNum[i] != '\0') {
        int val = get_hex_value(hexNum[i]); // Get integer value of current hex digit

        if (val != -1) { // Check if it's a valid hex digit
            printf("%s", hex_to_bin_map[val]); // Print corresponding binary string from lookup map
        } else {
            printf("\nError: Invalid hexadecimal digit '%c' found.\n", hexNum[i]);
            return 1; // Indicate error and exit
        }
        i++;
    }
    printf("\n");

    return 0;
}