Convert C++ String to Upper Case

In C++, converting a string into uppercase means changing all the characters into uppercase. This is a common requirement in many applications, such as formatting output, standard data input, and case sensitivity.

Following is the table that shows the conversion of string to uppercase:

• Using transform() function
• Using loop and toupper()
• Using for loop
• Using C-style string with toupper()

Uppercase Conversion Using transform() Function

The transform() is a simple C++ STL function that allows the user to perform a function for each value in the dataframe.

Syntax

Its syntax is as follows:

transform(str.begin(), str.end(), str.begin(), ::toupper);

Here,

• str.begin(), str.end(): Input range.
• str.begin(): It overwrite the original string.
• ::toupper: This is C function from the header <cctype> that uppercases each char.

Example

In this example, we use tranform() function to convert string to uppercase.

#include <iostream>
#include <string>
#include <algorithm>
using namespace std;

int main() {
   string str = "hello world";
   transform(str.begin(), str.end(), str.begin(), ::toupper);
   cout << str;
   return 0;
}

Output

The above program obtained the following result:

HELLO WORLD

Uppercase Conversion Using for Loop and toupper()

In this method, we manually iterate over the string and apply toupper() to each character.

Example

In this program, we iterate the characters through the string length() function and get the result in uppercase format.

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

int main() {
   string str = "TUTORIALSPOINT";
   for (int i = 0; i < str.length(); ++i) {
       str[i] = toupper(str[i]);
   }
    
   cout << str;
   return 0;
}

Output

The above program obtained the following result:

tutorialspoint

Uppercase Conversion Using R-based for Loop and toupper()

By using a C++ range-based for loop, convert any string type into uppercase.

Example

The example of the for loop is to set the range of string characters to convert into uppercase.

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

int main() {
   string str = "TUTORIX";
   for (char &ch : str) {
       ch = toupper(ch);
   }
   
   cout << str;
   return 0;
}

Output

The above program obtained the following result:

tutorix

Uppercase Conversion Using C-style String with toupper()

Suppose you are using a C-style character array; you can still use toupper() in a loop that changes the string into uppercase.

Example

In this program, we execute toupper() function to implement the conversion of string into uppercase.

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

int main() {
   char str[] = "c style string";
   for (int i = 0; str[i]; i++) {
       str[i] = toupper(str[i]);
   }
   
   cout << str;
   return 0;
}

Output

The above program obtained the following result:

C STYLE STRING