Accessing String Characters

Accessing String Characters

Characters inside a string live at numbered positions called indexes. The first character sits at index 0.

Bracket access

string word = "Hello";
cout << word[0] << endl;   // H
cout << word[1] << endl;   // e
cout << word[4] << endl;   // o

Indexes start at 0, so word[0] is the first character and word[4] is the last of a five-letter word.

Changing a character

word[0] = 'J';
cout << word << endl;   // Jello

Single characters are written with single quotes: 'J'.

The .at() method

cout << word.at(1) << endl;   // e

.at(index) does the same lookup, but it checks the bounds first.

Out-of-range risk

cout << word[99] << endl;   // undefined behavior!

With [] there is no bound check - reading past the end is your problem. .at(99) throws an exception instead. In most learning code, keep your indexes in range and life stays simple.

TL;DR

• Indexing starts at 0: word[0] is the first character.
• word[i] = 'x' changes a character (single quotes!).
• .at(i) is the bounds-checked version.
• Reading out of range with [] is undefined behavior.