toupper() in C++

In C++, toupper() is a library function used to convert a character from lowercase to uppercase. It is defined in the <cctype> (or <ctype.h>) header file.

• Processes a single character based on its ASCII value.
• Leaves uppercase letters, digits, and symbols unchanged.
• Commonly used for character-based transformations in strings.

#include <iostream>
#include <cctype>
using namespace std;

int main(){
    char ch = 'g';

    cout << "Original Character: " << ch << endl;
    cout << "Uppercase Character: " << (char)toupper(ch);

    return 0;
}

Original Character: g
Uppercase Character: G

Explanation: toupper() converts the lowercase character 'g' into its uppercase equivalent 'G'. The returned ASCII value is typecast to char before printing.

Syntax

toupper(int ch);

Parameter : ch - the character to be converted to uppercase.

Return Value

• Returns uppercase equivalent of the character.
• If input is already uppercase, a digit, or a symbol, it is returned unchanged.
• Returns an integer ASCII value (can be typecast to char).

We can manually typecast it to char using the syntax:

char c = (char) toupper('a');

Examples of toupper()

The following examples illustrates how to use toupper() in various scenarios.

Example: Program to convert a given lowercase alphabet to uppercase in C++.

#include <iostream>
using namespace std;

int main()
{
    char c = 'g';

    cout << c << " in uppercase is represented as = ";

    // toupper() returns an int value there for typecasting
    // with char is required
    cout << (char)toupper(c);

    return 0;
}

g in uppercase is represented as = G

Explanation: 'g' is passed to toupper(), which converts it to 'G', and the result is typecast to char before being displayed.

Example: Program to demonstrates how to convert a given string having lowercase alphabets to uppercase string in C++.

#include <iostream>
using namespace std;

int main()
{
    // string to be converted to uppercase
    string s = "geeksforgeeks";

    for (auto& x : s) {
        x = toupper(x);
    }

    cout << s;
    return 0;
}

GEEKSFORGEEKS

Explanation: The loop iterates through each character, toupper() converts lowercase letters to uppercase, and the entire string is transformed into uppercase.

Example: Program to demonstrates the behavior of toupper() when applied to uppercase letters, digits, and special symbols.

#include <iostream>
using namespace std;

int main()
{

    string s = "Geeks@123";

    for (auto x : s) {

        cout << (char)toupper(x);
    }

    return 0;
}

GEEKS@123

Explanation: Only alphabetic characters are converted to uppercase, while '@', '1', '2', and '3' remain unchanged.