Convert a character to uppercase in C++

This article will discuss different ways to convert a character to uppercase in C++.

Table of Contents

Convert a character to uppercase using toupper() function

C++ provides a function std::toupper(char c) to get a uppercase equivalent of a character. It accepts a character as an argument, and if this character is lowercase, it returns an uppercase equivalent of that character. We can use this function to convert a character to uppercase in C++. For example,

#include <iostream>

int main()
{
    char ch = 'i';
 
    // Convert a character to uppercase
    ch = std::toupper(ch);

    std::cout << ch <<std::endl;

    return 0;
}

Output:

I

It converted the lowercase character ‘i’ to an uppercase character ‘I’. If the provided character is not lowercase, then std::toupper() will return the same character. For example,

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#include <iostream>

int main()
{
    char ch = '+';
 
    // Convert a character to uppercase
    ch = std::toupper(ch);

    std::cout << ch <<std::endl;

    return 0;
}

Output:

+

The provided character is not a lowercase character; therefore toupper() returned the same character.

Convert a character to uppercase by using the ASCII values

Every character in C++ has an ASCII value associated with it. In C++, the ASCII values of uppercase characters (i.e. ‘A’ to ‘Z’) in C++ are 65 to 90. The ASCII values of lowercase characters (i.e. ‘a’ to ‘z’) in C++ are 97 to 122. So, to convert a lowercase character to uppercase, we can subtract 32 from the character(its ASCII value). When we subtract anything from a character, the character gets automatically converted to an int (i.e. the ascii value), and the value is subtracted. We can use this logic to convert a character to uppercase.

The steps are as follows,

  • Check if the provided character contains an alphabet and a lowercase character.
  • If yes, then subtract 32 from the character.

For example,

#include <iostream>

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

    // Check if char is a lowercase alphabet
    if( isalpha(ch) && islower(ch) )
    {
        // Convert a character to uppercase
        ch = ch - 32;
    }

    std::cout << ch <<std::endl;

    return 0;
}

Output:

I

It converted the lowercase character ‘i’ to an uppercase character ‘I’. Let’s check a negative example and convert the character ‘+’ to uppercase.

For example,

#include <iostream>

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

    // Check if char is a lowercase alphabet
    if( isalpha(ch) && islower(ch) )
    {
        // Convert a character to uppercase
        ch = ch - 32;
    }

    std::cout << ch <<std::endl;

    return 0;
}

Output:

+

The provided character is not a lowercase character; therefore, our code didn’t change its value.

Summary:

We learned about two different ways to convert a character to uppercase in C++.

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Thanks for reading.

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