Example: Letter to Phone Number Converter (switch) in C

// Letter to Phone Number Converter (switch)
#include <stdio.h>
#include <string.h> // For strlen()
#include <ctype.h>  // For toupper()

void convertLettersToPhoneNumberSwitch(char *str) {
    for (int i = 0; str[i] != '\0'; i++) {
        char ch = toupper(str[i]); // Convert to uppercase for consistent checking

        switch (ch) {
            case 'A': case 'B': case 'C':
                str[i] = '2';
                break;
            case 'D': case 'E': case 'F':
                str[i] = '3';
                break;
            case 'G': case 'H': case 'I':
                str[i] = '4';
                break;
            case 'J': case 'K': case 'L':
                str[i] = '5';
                break;
            case 'M': case 'N': case 'O':
                str[i] = '6';
                break;
            case 'P': case 'Q': case 'R': case 'S':
                str[i] = '7';
                break;
            case 'T': case 'U': case 'V':
                str[i] = '8';
                break;
            case 'W': case 'X': case 'Y': case 'Z':
                str[i] = '9';
                break;
            default:
                // Non-alphabetic characters (digits, hyphens, etc.)
                // are left unchanged by default
                break;
        }
    }
}

int main() {
    // Step 1: Declare character arrays for input.
    char phoneNumber1[50] = "1-800-C-A-L-L-N-O-W";
    char phoneNumber2[50] = "Programming-isfun";

    // Step 2: Print original strings.
    printf("Original: %s\n", phoneNumber1);
    printf("Original: %s\n", phoneNumber2);

    // Step 3: Convert letters to phone number digits using the switch approach.
    convertLettersToPhoneNumberSwitch(phoneNumber1);
    convertLettersToPhoneNumberSwitch(phoneNumber2);

    // Step 4: Print converted strings.
    printf("Converted: %s\n\n", phoneNumber1);
    printf("Converted: %s\n\n", phoneNumber2);

    return 0;
}