Strings are one of the most important data types in C++ programming. They are used for storing and manipulating text in applications ranging from simple input/output to complex text processing. Often, developers need to convert strings to uppercase or lowercase, remove spaces, or manipulate individual characters to format text properly. This article covers a comprehensive guide on string case conversion and manipulation in C++.
By the end of this post, you will know how to use functions like toupper() and tolower(), iterate through strings for character-level modifications, remove unwanted characters, and format names or sentences efficiently.
Understanding String Manipulation
String manipulation involves performing operations on strings to change their content, format, or structure. Common operations include:
- Changing the case of letters (uppercase or lowercase)
- Removing spaces or punctuation
- Extracting substrings
- Replacing characters
- Formatting text to meet certain standards
These operations are widely used in real-world applications such as:
- Formatting user input
- Validating text fields
- Standardizing data for storage or comparison
- Implementing search functionality
Changing String Case Using toupper() and tolower()
C++ provides the toupper() and tolower() functions through the <cctype> library. These functions are used to convert a single character to uppercase or lowercase, respectively.
Syntax
int toupper(int ch);
int tolower(int ch);
chis the character to convert.- Both functions return the converted character as an integer type, which can be stored in a
charvariable.
Example: Converting a Single Character
#include <iostream>
#include <cctype>
using namespace std;
int main() {
char ch = 'a';
char upperCh = toupper(ch);
char lowerCh = tolower('B');
cout << "Original: " << ch << endl;
cout << "Uppercase: " << upperCh << endl;
cout << "Lowercase: " << lowerCh << endl;
return 0;
}
Output:
Original: a
Uppercase: A
Lowercase: b
Explanation:
toupper('a')converts'a'to'A'.tolower('B')converts'B'to'b'.
Iterating Through a String to Change Case
While toupper() and tolower() work on individual characters, you often need to convert an entire string. This can be done by iterating through the string and applying the functions to each character.
Example: Converting a String to Uppercase
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main() {
string text = "Hello World!";
for (int i = 0; i < text.length(); i++) {
text[i] = toupper(text[i]);
}
cout << "Uppercase: " << text << endl;
return 0;
}
Output:
Uppercase: HELLO WORLD!
Explanation:
- The
forloop iterates through each character in the string. toupper()converts each character to uppercase.
Example: Converting a String to Lowercase
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main() {
string text = "Hello World!";
for (int i = 0; i < text.length(); i++) {
text[i] = tolower(text[i]);
}
cout << "Lowercase: " << text << endl;
return 0;
}
Output:
Lowercase: hello world!
Using Range-based Loops for Case Conversion
C++11 introduced range-based for loops, which simplify iterating through containers like strings.
Example: Uppercase Conversion Using Range-based Loop
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main() {
string text = "Good Morning!";
for (char &ch : text) {
ch = toupper(ch);
}
cout << "Uppercase: " << text << endl;
return 0;
}
Explanation:
- The
char &chreference allows modifying the original string directly. - The loop iterates through all characters in the string without using an index.
Removing Spaces or Special Characters
String manipulation often involves removing unwanted characters, such as spaces, punctuation, or special symbols. This is particularly useful for normalizing text before storage or comparison.
Example: Removing Spaces
#include <iostream>
#include <string>
using namespace std;
int main() {
string text = "Hello World! Welcome to C++.";
string result = "";
for (char ch : text) {
if (ch != ' ') {
result += ch;
}
}
cout << "Without spaces: " << result << endl;
return 0;
}
Output:
Without spaces: HelloWorld!WelcometoC++.
Explanation:
- Each character is checked, and spaces are excluded from the result string.
Example: Removing Special Characters
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main() {
string text = "Hello, World! 123";
string result = "";
for (char ch : text) {
if (isalnum(ch) || ch == ' ') { // Keep only letters, numbers, and spaces
result += ch;
}
}
cout << "Alphanumeric only: " << result << endl;
return 0;
}
Output:
Alphanumeric only: Hello World 123
Explanation:
- The
isalnum()function checks whether a character is a letter or a digit. - Only alphanumeric characters and spaces are added to the new string.
Formatting Names or Sentences
String manipulation is often used to format names or sentences, such as capitalizing the first letter of each word or normalizing input.
Example: Capitalizing the First Letter of Each Word
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main() {
string text = "hello world from c++";
bool capitalize = true;
for (char &ch : text) {
if (capitalize && isalpha(ch)) {
ch = toupper(ch);
capitalize = false;
} else if (ch == ' ') {
capitalize = true;
} else {
ch = tolower(ch);
}
}
cout << "Formatted: " << text << endl;
return 0;
}
Output:
Formatted: Hello World From C++
Explanation:
- The
capitalizeflag ensures the first letter of each word is converted to uppercase. - Remaining letters are converted to lowercase.
- Spaces reset the
capitalizeflag for the next word.
Example: Converting Entire Sentence to Lowercase Before Formatting
#include <iostream>
#include <string>
#include <cctype>
using namespace std;
int main() {
string text = "hELLo WOrLD fRoM c++";
// Convert entire string to lowercase
for (char &ch : text) {
ch = tolower(ch);
}
// Capitalize the first letter of each word
bool capitalize = true;
for (char &ch : text) {
if (capitalize && isalpha(ch)) {
ch = toupper(ch);
capitalize = false;
} else if (ch == ' ') {
capitalize = true;
}
}
cout << "Properly formatted: " << text << endl;
return 0;
}
Output:
Properly formatted: Hello World From C++
Explanation:
- Converting to lowercase first ensures uniformity.
- Capitalizing the first letter of each word gives a clean, professional format.
Using erase() and remove() to Manipulate Strings
C++ provides the erase() function in the std::string class to remove characters at specific positions. Combining it with the remove() algorithm allows removing all occurrences of a character.
Example: Removing All Spaces
#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
int main() {
string text = "Remove all spaces";
text.erase(remove(text.begin(), text.end(), ' '), text.end());
cout << "Without spaces: " << text << endl;
return 0;
}
Output:
Without spaces: Removeallspaces
Explanation:
remove()shifts unwanted characters to the end.erase()trims the shifted characters, leaving the cleaned string.
Combining Multiple Manipulations
You can combine multiple string manipulations, such as removing special characters, converting case, and formatting words, into a single process.
Example: Cleaning and Formatting a Sentence
#include <iostream>
#include <string>
#include <cctype>
#include <algorithm>
using namespace std;
int main() {
string text = " hELLo, WoRLD! welcome-to c++ programming. ";
// Remove unwanted characters
text.erase(remove_if(text.begin(), text.end(), [](char ch){
return !isalnum(ch) && ch != ' ';
}), text.end());
// Convert to lowercase
for (char &ch : text) {
ch = tolower(ch);
}
// Capitalize first letter of each word
bool capitalize = true;
for (char &ch : text) {
if (capitalize && isalpha(ch)) {
ch = toupper(ch);
capitalize = false;
} else if (ch == ' ') {
capitalize = true;
}
}
cout << "Formatted: " << text << endl;
return 0;
}
Output:
Formatted: Hello World Welcome To C Programming
Explanation:
- Special characters like commas, dashes, and periods are removed.
- The entire string is converted to lowercase first.
- The first letter of each word is capitalized for readability.
Best Practices for String Case Conversion and Manipulation
- Use
std::stringover C-style strings for easier manipulation. - Use
toupper()andtolower()for character-level changes. - Iterate through strings with references to avoid unnecessary copies.
- Normalize strings before comparison (convert to lowercase or uppercase).
- Use
erase()andremove()for efficient character removal. - Use proper formatting techniques when working with names, sentences, or input from users.
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