How Do You Change Lowercase Letters to Uppercase in C++?

Excerpt§

This article explains different techniques like toupper(), transform algorithms, loops, and stringstreams to change lowercase letters to uppercase in C++ strings.

C++ provides several straightforward ways to convert lowercase characters in a string to uppercase. This includes built-in functions like toupper(), algorithms like transform(), and stringstreams.

Let’s explore some common techniques for changing lowercase to uppercase in C++ code.

Introduction§

When working with string data in C++, you may need to standardize the case by converting lowercase letters to uppercase. Here are some approaches:

• toupper() function - Simple uppercase conversion
• transform algorithm - Apply toupper() to entire strings
• for loops - Manual iteration and transformation
• stringstreams - Set uppercase format flag
• online tools - Quick case conversion

We’ll walk through code examples of each method for changing case in C++ strings.

toupper() Function§

The toupper() function in the header is used to convert a single character to uppercase:

 1#include <iostream>
 2#include <cctype>
 3
 4int main() {
 5
 6  char lower = 'a';
 7  char upper = toupper(lower);
 8
 9  std::cout << upper << std::endl; // 'A'
10
11  return 0;
12}
cpp

toupper() takes a char as input and returns its uppercase form.

transform Algorithm§

To uppercase an entire string, we can use the transform algorithm from :

 1#include <iostream>
 2#include <algorithm>
 3#include <cctype>
 4
 5int main() {
 6
 7  std::string lower = "hello world";
 8
 9  transform(lower.begin(), lower.end(), lower.begin(), ::toupper);
10
11  std::cout << lower << std::endl; // "HELLO WORLD"
12
13  return 0;
14}
cpp

transform applies toupper() to each character of the string in place.

for Loops§

For more manual control, iterate through the string yourself with a for loop:

 1#include <iostream>
 2
 3int main() {
 4
 5  std::string lower = "hello world";
 6
 7  for(int i=0; i<lower.length(); i++) {
 8    lower[i] = toupper(lower[i]);
 9  }
10
11  std::cout << lower << std::endl; // "HELLO WORLD"
12
13  return 0;
14}
cpp

This loops through each character and uppercases it.

Free Online Case Conversion Tools§

For quick case conversion, sites like String to Uppercase are handy.

Paste your C++ string and get the uppercase version without any coding!

Learn more click here

String Streams§

C++ string streams can be configured to output strings in uppercase:

 1#include <iostream>
 2#include <sstream>
 3
 4int main() {
 5
 6  std::string lower = "hello world";
 7
 8  std::stringstream ss;
 9  ss << std::uppercase << lower;
10
11  std::string upper = ss.str();
12
13  std::cout << upper << std::endl; // "HELLO WORLD"
14
15  return 0;
16}
cpp

The uppercase flag formats the inserted string as uppercase.

Use Cases§

Some common use cases for uppercase conversion in C++ include:

• Sanitizing user input into a standard format
• Defining constants in uppercase by convention
• Performing case-insensitive string comparisons

Uppercase strings have many applications across C++ programs.

Conclusion§

In C++, transforming lowercase strings to uppercase can be done easily using:

• toupper() for single characters
• transform with toupper() for full strings
• for loops to iterate through each character
• stringstreams configured for uppercase
• online conversion tools

The toupper() function and transform algorithm provide the most direct way to change case in C++.

Converting strings to uppercase or lowercase is a useful technique for string processing and comparison in C++.