String Basics

We’ve been using strings since the Hello World lesson — every time you write "Hello, World!", that’s a string. But strings in C++ can do much more than just hold static text. You can combine, slice, measure, and compare strings. In this lesson, we’ll master the fundamentals of string manipulation.

What Is a String?

Think of a string as a bead necklace. Each bead is a single character — a letter, digit, symbol, or space. You can count how many beads there are, add new beads, pick out a specific bead, or cut off part of the necklace.

String "Hello"  ->  ['H'] ['e'] ['l'] ['l'] ['o']
                     0     1     2     3     4     <- position (index)

Each character has a position (index) that starts from 0 — not 1. This is a common convention in virtually all programming languages.

Declaring Strings

#include <iostream>
#include <string>    // Don't forget to include this!

int main() {
    std::string greeting = "Hello, world!";
    std::string firstName = "Budi";
    std::string lastName = "Santoso";
    std::string empty = "";     // An empty string — valid!

    std::cout << greeting << std::endl;

    return 0;
}

Concatenation (Combining)

You can combine two strings using the + operator:

#include <iostream>
#include <string>

int main() {
    std::string firstName = "Budi";
    std::string lastName = "Santoso";

    std::string fullName = firstName + " " + lastName;

    std::cout << "Full name: " << fullName << std::endl;

    return 0;
}

Output:

Full name: Budi Santoso

Notice: we added " " (a string containing a space) between the first and last name. Without it, the result would be "BudiSantoso" — stuck together without a space.

Concatenation with +=

You can also append text to an existing string:

#include <iostream>
#include <string>

int main() {
    std::string message = "Hello";
    std::cout << "Before: " << message << std::endl;

    message += ", ";
    message += "how are you";
    message += "?";
    std::cout << "After: " << message << std::endl;

    return 0;
}

Output:

Before: Hello
After: Hello, how are you?

std::string text = "My age is " + std::to_string(17) + " years";

Measuring String Length

To find out how many characters are in a string, use .length() or .size() — both produce the same result:

#include <iostream>
#include <string>

int main() {
    std::string word = "Programming";

    std::cout << "Word: " << word << std::endl;
    std::cout << "Length (length): " << word.length() << std::endl;
    std::cout << "Length (size): " << word.size() << std::endl;

    std::string empty = "";
    std::cout << "Empty string length: " << empty.length() << std::endl;

    return 0;
}

Output:

Word: Programming
Length (length): 11
Length (size): 11
Empty string length: 0

length() and size() count all characters, including spaces:

std::string sentence = "Hello World";
std::cout << sentence.length() << std::endl;  // 11 (including the space)

Accessing Individual Characters

You can access a specific character using an index in square brackets []:

#include <iostream>
#include <string>

int main() {
    std::string word = "Hello";

    std::cout << "Character at 0: " << word[0] << std::endl;  // H
    std::cout << "Character at 1: " << word[1] << std::endl;  // e
    std::cout << "Character at 4: " << word[4] << std::endl;  // o

    return 0;
}

Output:

Character at 0: H
Character at 1: e
Character at 4: o

Extracting a Portion with substr()

substr() (substring) extracts a part of the text from a string. The format is:

string.substr(start_position, character_count)

#include <iostream>
#include <string>

int main() {
    std::string sentence = "Learning C++ is fun!";

    std::string part1 = sentence.substr(0, 8);      // "Learning"
    std::string part2 = sentence.substr(9, 3);       // "C++"
    std::string part3 = sentence.substr(16);          // "fun!" (to the end)

    std::cout << "Part 1: " << part1 << std::endl;
    std::cout << "Part 2: " << part2 << std::endl;
    std::cout << "Part 3: " << part3 << std::endl;

    return 0;
}

Output:

Part 1: Learning
Part 2: C++
Part 3: fun!

If you don’t provide the second parameter (character count), substr() takes all characters from the starting position to the end of the string.

Comparing Strings

Strings can be compared using comparison operators:

#include <iostream>
#include <string>

int main() {
    std::string a = "hello";
    std::string b = "hello";
    std::string c = "Hello";

    if (a == b) {
        std::cout << "a and b are the same" << std::endl;
    }

    if (a != c) {
        std::cout << "a and c are different" << std::endl;
    }

    return 0;
}

Output:

a and b are the same
a and c are different

String comparison is case-sensitive — "hello" and "Hello" are two different strings because uppercase and lowercase letters are distinguished.

You can also compare strings lexicographically (dictionary order) using <, >, <=, >=:

std::string apple = "apple";
std::string banana = "banana";

if (apple < banana) {
    std::cout << "apple comes before banana in the dictionary" << std::endl;
}

Finding Text in a String

find() locates the position of the first occurrence of a text within a string:

#include <iostream>
#include <string>

int main() {
    std::string sentence = "I love learning C++";

    int position = sentence.find("learning");

    if (position != std::string::npos) {
        std::cout << "'learning' found at position " << position << std::endl;
    } else {
        std::cout << "Not found" << std::endl;
    }

    return 0;
}

Output:

'learning' found at position 7

std::string::npos is a special value meaning “not found”. If find() returns npos, it means the text you’re searching for doesn’t exist in the string.

Full Program: Username Generator

#include <iostream>
#include <string>

int main() {
    std::string firstName;
    std::string lastName;
    int birthYear;

    std::cout << "=== Username Generator ===" << std::endl;

    std::cout << "First name: ";
    std::cin >> firstName;

    std::cout << "Last name: ";
    std::cin >> lastName;

    std::cout << "Birth year: ";
    std::cin >> birthYear;

    // Create username: first 3 letters of first name + last name + last 2 digits of year
    std::string username = firstName.substr(0, 3) + lastName + std::to_string(birthYear % 100);

    std::cout << "\nYour username: " << username << std::endl;
    std::cout << "Username length: " << username.length() << " characters" << std::endl;

    return 0;
}

Example interaction:

=== Username Generator ===
First name: Rina
Last name: Sari
Birth year: 2009

Your username: RinSari09
Username length: 9 characters

#include <iostream>
#include <string>

int main() {
  std::string first = "Budi";
  std::string last = "Santoso";
  std::string fullName = first  " "  last;
  std::cout << fullName << std::endl;
  return 0;
}

Exercises

Create a program that:

1. Asks for a first name and last name (one word each)
2. Combines them into a full name
3. Displays the full name, total character count, and initials (first letter of first name + first letter of last name)

Example interaction:

First name: Ahmad
Last name: Fauzi

Full name: Ahmad Fauzi
Character count: 11
Initials: AF

Hint: use [0] to get the first character, and length() to count the length.

Summary

• std::string stores text, requires #include <string>
• Concatenation (+, +=): combining strings
• .length() / .size(): count the number of characters
• [index]: access a character at a specific position (starting from 0)
• .substr(pos, len): extract a portion of a string
• ==, !=, <, >: compare strings (case-sensitive)
• .find(text): find the position of text within a string
• std::to_string(number): convert a number to a string

In the next lesson, we’ll learn about constants and the auto keyword — how to create variables that can’t be changed and let the compiler figure out the data type.