Strings — C-Style & std::string

Two Kinds of Strings in C++

C++ actually has two ways to represent text: the old C-style string inherited from the C language (a plain array of characters), and the modern std::string class from the <string> header. Almost all real C++ code written today uses std::string — but you'll still see C-style strings in older code, so it's worth understanding both.

C-Style Strings (Historical Context)

A C-style string is just a char array where the last meaningful character is followed by a special null terminator, written '\0'. Functions that print or process C-style strings scan forward until they hit that null character to know where the text ends.

// cstyle_strings.cpp
#include <iostream>
using namespace std;

int main() {
    char name[6] = {'H', 'e', 'l', 'l', 'o', '\0'};
    cout << name << endl;

    char greeting[] = "Hi there";  // compiler adds '\0' automatically
    cout << greeting << endl;

    return 0;
}

std::string Basics

To use std::string, include the <string> header. You can concatenate strings directly with +, and check their length with .length() or the equivalent .size().

// string_basics.cpp
#include <iostream>
#include <string>
using namespace std;

int main() {
    string first = "Ada";
    string last = "Lovelace";
    string full = first + " " + last;

    cout << full << endl;
    cout << "Length: " << full.length() << endl;
    cout << "Size: " << full.size() << endl;

    return 0;
}

.length() and .size() return exactly the same value — they're two names for the same thing. Most C++ programmers use whichever reads more naturally in context.

Indexing & Substrings

You can access individual characters of a std::string with square brackets, exactly like an array. To pull out a piece of a string, use .substr(start, length).

// string_slicing.cpp
#include <iostream>
#include <string>
using namespace std;

int main() {
    string word = "BitWithBite";

    cout << "First char: " << word[0] << endl;
    cout << "Last char: " << word[word.length() - 1] << endl;
    cout << "Substring(3,4): " << word.substr(3, 4) << endl;

    return 0;
}

Searching & Comparing Strings

Use .find() to search for a substring inside a string. It returns the starting index if found, or the special value string::npos if not found. You can compare two strings directly with ==, !=, <, and >.

// string_search.cpp
#include <iostream>
#include <string>
using namespace std;

int main() {
    string sentence = "C++ is powerful and fast";

    size_t pos = sentence.find("powerful");
    if (pos != string::npos) {
        cout << "Found at index: " << pos << endl;
    } else {
        cout << "Not found" << endl;
    }

    string a = "apple";
    string b = "banana";
    if (a == b) {
        cout << "Equal" << endl;
    } else {
        cout << "Not equal" << endl;
    }

    return 0;
}

size_t is an unsigned integer type used for sizes and indices throughout the C++ standard library — you'll see it a lot alongside strings, arrays, and containers.

Converting Between Numbers and Strings

Use std::to_string() to turn a number into a string, and std::stoi() ("string to int") to turn a numeric string back into an int. There are related functions like stod() for doubles.

// string_convert.cpp
#include <iostream>
#include <string>
using namespace std;

int main() {
    int age = 21;
    string ageText = to_string(age);
    cout << "I am " + ageText + " years old" << endl;

    string numStr = "142";
    int num = stoi(numStr);
    cout << "num + 8 = " << (num + 8) << endl;

    return 0;
}

Lesson Summary

Let's recap everything you learned in this lesson: