Write a program with three functions: upper , lower , and reverse .

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As for answering your question. Below is the C++ program implementing the upper, lower, and reverse functions:

#include <iostream>
#include <cctype>  // For toupper() and tolower()
#include <cstring> // For strlen()

using namespace std;

// Function to convert string to uppercase
void upper(char *str) {
    while (*str) {
        *str = toupper(*str);
        str++;
    }
}

// Function to convert string to lowercase
void lower(char *str) {
    while (*str) {
        *str = tolower(*str);
        str++;
    }
}

// Function to reverse case of each character in the string
void reverse(char *str) {
    while (*str) {
        if (islower(*str))
            *str = toupper(*str);
        else if (isupper(*str))
            *str = tolower(*str);
        str++;
    }
}

int main() {
    const int SIZE = 100;  // Maximum string size
    char input[SIZE];

    // Asking the user for a string input
    cout << "Enter a string: ";
    cin.getline(input, SIZE);

    // Apply the functions in the required order
    reverse(input);
    cout << "Reversed case: " << input << endl;

    lower(input);
    cout << "Lowercase: " << input << endl;

    upper(input);
    cout << "Uppercase: " << input << endl;

    return 0;
}