Example: Case Conversion using ctype.h in C

// Case Conversion using ctype.h
#include <stdio.h>
#include <string.h> // For strlen
#include <ctype.h>  // For tolower, toupper

// Function to convert string to lowercase
void toLowerCase(char *str) {
    for (int i = 0; str[i] != '\0'; i++) {
        str[i] = tolower((unsigned char)str[i]);
    }
}

// Function to convert string to uppercase
void toUpperCase(char *str) {
    for (int i = 0; str[i] != '\0'; i++) {
        str[i] = toupper((unsigned char)str[i]);
    }
}

int main() {
    // Step 1: Define a string for conversion
    char myString1[] = "Hello World 123!";
    char myString2[] = "Another EXAMPLE String.";
    char myString3[] = "miXeD cAsE.";

    // Step 2: Convert to lowercase and print
    printf("Original: \"%s\"\n", myString1);
    toLowerCase(myString1);
    printf("Lowercase: \"%s\"\n\n", myString1);

    // Step 3: Convert to uppercase and print
    printf("Original: \"%s\"\n", myString2);
    toUpperCase(myString2);
    printf("Uppercase: \"%s\"\n\n", myString2);

    // Step 4: Demonstrate both conversions
    printf("Original: \"%s\"\n", myString3);
    toLowerCase(myString3);
    printf("Lowercase: \"%s\"\n", myString3);
    toUpperCase(myString3); // Convert the already lowercased string to uppercase
    printf("Uppercase: \"%s\"\n\n", myString3);

    return 0;
}