Arrays and Strings

Store many values in a row, and work with text

Big Idea: Sometimes you need to keep many values, not just one. An array is a row of boxes that all hold the same type of value. A string is a special kind of sequence made of characters — it is how C++ keeps text.

By the end you will be able to:

make a fixed-size array and read its elements by index,
loop over an array to add up or check every value,
store text in a std::string and use its common methods.

1. What is an array?

An array is a group of values of the same type, stored next to each other in memory. Think of an egg carton: it has a fixed number of cups in a row, and each cup holds one egg. An array cup is called an element.

Two important rules:

Fixed size. When you make a plain array you choose how many boxes it has, and that number does not change.
Zero-based index. The boxes are numbered starting at 0. So an array of 5 elements uses indices 0, 1, 2, 3, 4 — the last index is one less than the size.

2. Making an array and reading elements

You declare an array by writing the type, a name, and the size in square brackets. You can fill it with values inside { }. You read a single element with its index in square brackets.

#include <iostream>
using namespace std;

int main() {
    int scores[5] = {90, 85, 100, 70, 95};
    cout << scores[0] << endl;  // first element (index 0)
    cout << scores[4] << endl;  // last element  (index 4)
    return 0;
}

// Output:
// 90
// 95

Here is how those five numbers sit in memory. The blue boxes are the values; the orange numbers underneath are the indices you use to reach them:

An array of 5 scores. Index 0 is the first box, index 4 is the last.

scores[0] is 90 and scores[4] is 95. There is no scores[5] — that box does not exist!

Arrays and Strings