## Chapter 9: Strings So far, we have seen numbers, arrays, and loops. But most real-world programs work with text (names, messages, input, output). That's why strings are very important. ### What is a string? (Simple Language) String means: A sequence of characters For example: - Names - Sentences - Messages Examples: C++ ``` "Hello" "Welcome to C++" "Rahul Sharma" ``` Two ways to handle strings in C++: 1. C-style strings (character array) 2. C++ string class (this is what we will learn) **String class:** - Easy to use - Safe - Standard in modern C++ **Using the C++ String Class** For this, we need: C++ ``` #include <string> ``` **Example: String Operations** C++ ``` #include <iostream> #include <string> using namespace std; int main() { string firstWord = "Hello"; string secondWord = "C++"; // 1. Concatenation string sentence = firstWord + " " + secondWord; // 2. Length cout << "Length: " << sentence.length() << endl; // 3. First character cout << "First character: " << sentence[0] << endl; // 4. Substring string part = sentence.substr(0, 5); cout << "Substring: " << part << endl; // 5. Finding a word int position = sentence.find("C++"); cout << "Position: " << position << endl; // 6. Comparison if (firstWord == "Hello") { cout << "String matched!" << endl; } // 7. Inputting a whole line string fullName; cout << "Enter your full name: "; getline(cin, fullName); cout << "Hello, " << fullName << endl; return 0; } ``` Now let's understand each concept in simple language: 1. String Concatenation C++ ``` string sentence = firstWord + " " + secondWord; ``` - Strings can be joined using the + operator. - A space " " is also a string. Result: C++ ``` Hello C++ ``` 1. String Length C++ ``` sentence.length() ``` - Returns the number of characters. - Spaces are also counted. The length of "Hello C++" = 9 1. Accessing Characters C++ ``` sentence[0] ``` - Index starts from 0. - Returns the first character. Result: H 1. Extracting Substring C++ ``` sentence.substr(0, 5) ``` Meaning: - Starts from index 0 - Takes 5 characters Result: "Hello" 1. Finding in a String (find) C++ ``` sentence.find("C++") ``` - Returns the starting index of the substring. - If not found → returns -1. 1. String Comparison C++ ``` if (firstWord == "Hello") ``` - In C++, strings can be compared directly using ==. - This is very easy and safe. 1. Inputting the Entire Line (getline) C++ ``` getline(cin, fullName); ``` - Reads the entire line, including spaces. - Best for names, sentences, and addresses. `cin >>` stops at a space, but `getline` does not. **Common String Functions (Quick Look)** | Function | Purpose | | :--- | :--- | | `length()` | Get size | | `substr()` | Extract part | | `find()` | Search | | `+` | Concatenate | | `==` | Compare | **Beginner Tips** - Always include <string> - Use getline for text input - Index starts from 0 - Strings and characters are different things Real-Life Uses - Login system - Search feature - Chat messages - File names Remember in One Line Text is → string Need space → getline Comparison is easy → string class **Common String Functions:** C++'s string class is powerful because it provides built-in useful functions. With these functions you can: - Get the length of a string - Extract a part of it - Change text - Concatenate - Delete without extra effort **Example String (New Example)** C++ ``` string line = "Learn C++ Easily"; ``` Now let's perform different operations on this string. 1. length() – Finding the length C++ ``` line.length(); ``` - Total number of characters in the string - Spaces are also counted "Learn C++ Easily" → length = 16 1. substr() – Extracting a substring C++ ``` line.substr(6, 3); ``` Meaning: - Start from index 6 - Extract 3 characters Result: Code snippet ``` C++ ``` Remember the format: C++ ``` substr(startIndex, numberOfCharacters) ``` 1. find() – Finding text C++ ``` line.find("C++"); ``` - Tells where the text starts - If not found → -1 In "Learn C++ Easily", "C++" starts at index 6 1. replace() – Replacing text C++ ``` line.replace(6, 3, "Java"); ``` Meaning: - From index 6 - Remove 3 characters - Insert "Java" in their place Result: Nginx ``` Learn Java Easily ``` 1. insert() – Inserting text in the middle C++ ``` line.insert(5, "to "); ``` Meaning: - Insert "to " at index 5 - The rest of the text will shift forward Result: ``` Learn to C++ Easily ``` 6. erase() – deleting text ```cpp line.erase(0, 6); ``` Meaning: - From index 0 - Remove 6 characters Result: Code snippet ``` C++ Easily ``` Format: C++ ``` erase(startIndex, length) ``` 1. append() – adding at the end C++ ``` line.append("!"); ``` - Adds to the end of the string Result: Code snippet ``` Learn C++ Easily! ``` **All functions together (Mini Demo)** C++ ``` #include <iostream> #include <string> using namespace std; int main() { string text = "Learn C++ Easily"; cout << text.length() << endl; cout << text.substr(6, 3) << endl; cout << text.find("C++") << endl; text.replace(6, 3, "Python"); cout << text << endl; return 0; } ``` **Beginner Tips (Very Important)** - Index always starts from 0 - Checking the result of find() is good practice - replace, erase, insert modify the original string - An out-of-range index can cause the program to crash Remember in One Line - length → size - substr → part - find → find - replace → replace - insert → insert - erase → remove - append → add