Strings (std::string)

std::string is the safe, flexible way to handle text in C++. It grows on demand, manages its own memory, and comes with a rich toolkit for joining, searching, slicing, and transforming text. This lesson takes you from + concatenation to bounds-checked access, searching with find , and converting between strings and numbers.

Learn Strings (std::string) in our free C++ course — a beginner-friendly interactive lesson with worked examples, a practice exercise and a quick recall.

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A std::string is like a magnetic letter board that resizes itself. You can snap letters on the end ( += ), read the letter at any slot ( s[3] ), search for a word ( find ), or peel off a strip of letters ( substr ) — and the board automatically makes room when you add more. A raw char[] array, by contrast, is a fixed-size board: run out of slots and letters spill off the edge, corrupting whatever is next to it in memory. That spill is the infamous buffer overflow, and std::string exists to prevent it.

1. Creating & Joining Strings

Build text with + to concatenate and += to append in place. .size() (or its synonym .length() ) gives the character count, .front() / .back() read the ends, and .empty() checks for an empty string.

2. Accessing Characters

Index individual characters with s[i] starting from 0 . For untrusted indexes prefer s.at(i) , which throws std::out_of_range instead of silently reading garbage. A range-based for visits every character in turn.

3. Searching & Slicing

find returns the index of a substring, or the special value string::npos when it isn't there — always test against npos , never -1 . substr(start, length) extracts a slice, and replace swaps out a section.

4. Converting Between Strings & Numbers

to_string turns a number into text (handy for building messages), while stoi and stod parse text back into an int or double . Note that to_string(4.5) prints with trailing zeros — use formatting if you need control.

5. Transforming Text

Combine std::transform with toupper / tolower to change case, and the erase-remove idiom to strip characters. These standard-library tools are faster and clearer than hand-written loops once you recognize the pattern.

Your turn. Build a username and report its length:

These lines should find a word and print the text after it. Reorder them so the program prints fox .

Why: first you need the string (A), then locate "fox" with find (B). You must check the result against string::npos (C) before using it, because substr with an out-of-range index would throw. Only then is it safe to slice from p to the end (D), giving fox . Return last (E).

Predict the output before revealing each answer.

cde — substr(2, 3) starts at index 2 and takes 3 characters.

1 — "z" isn't in "cat" , so find returns npos and the comparison is true (prints as 1).

46 — both strings are parsed to ints first, so it's numeric addition (12 + 34), not string concatenation.

Read a full name and print the initials, each followed by a period. Match the expected output in the comments.

Practice quiz

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