 # Arrays.

## Presentation on theme: "Arrays."— Presentation transcript:

Arrays

Introduction to Arrays
An array is used to process a collection of data of the same type Examples: A list of names A list of temperatures Why do we need arrays? Imagine keeping track of 5 test scores, or 100, or in memory How would you name all the variables? How would you process each of the variables?

Arrays An array is a collection of data elements that are of the same type (e.g., a collection of integers, collection of characters, collection of doubles).

Array Applications Given a list of test scores, determine the maximum and minimum scores. Read in a list of student names and rearrange them in alphabetical order (sorting). Given the height measurements of students in a class, output the names of those students who are taller than average.

Array Declaration Syntax:
<type> <arrayName>[<array_size>] Ex. int Ar; The array elements are all values of the type <type>. The size of the array is indicated by <array_size>, the number of elements in the array. <array_size> must be an int constant or a constant expression. Note that an array can have multiple dimensions.

Array Declaration // array of 10 uninitialized ints int Ar; -- Ar
4 5 6 3 2 8 9 7 1 1 2 3 4 5

Subscripting Declare an array of 10 integers:
int Ar; // array of 10 ints To access an individual element we must apply a subscript to array named Ar. A subscript is a bracketed expression. The expression in the brackets is known as the index. First element of array has index 0. Ar Second element of array has index 1, and so on. Ar, Ar, Ar,… Last element has an index one less than the size of the array. Ar Incorrect indexing is a common error.

Subscripting 1 // array of 10 uninitialized ints int Ar;
int x = Ar; 1 -- -- 1 Ar 4 5 6 3 2 8 9 7 Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar

Loops And Arrays for-loops are commonly used to step through arrays
Example: for (i = 0; i < 5; i++) { cout << score[i] << " off by " << (max – score[i]) << endl; } could display the difference between each score and the maximum score stored in an array Last index is (size – 1) First index is 0

Variables and Declarations
Most compilers do not allow the use of a variable to declare the size of an array Example: cout << "Enter number of students: "; cin >> number; int score[number]; This code is illegal on many compilers

Subscripting Example //For loop to fill & print a 10-int array
int main ( ) { int index, ar; // array for 10 integers // Read in 10 elements. cout << "Enter 10 integers: "; for(index = 0; index < 10; index ++) cin >> ar[index]; cout << endl; cout << "The integers are "; cout << ar[index] << " "; return 0; }

Array Element Manipulation
Consider int Ar, i = 7, j = 2, k = 4; Ar = 1; Ar[i] = 5; Ar[j] = Ar[i] + 3; Ar[j+1] = Ar[i] + Ar; Ar[Ar[j]] = 12; cin >> Ar[k]; //where the next input value is 3 -- 8 6 1 Ar 5 3 12 4 2 9 7 Ar Ar Ar Ar Ar Ar Ar Ar Ar Ar

Array Initialization 6 -1 Ar = -1;
int Ar = {9, 8, 7, 6, 5, 4, 3, 2, 1, 0}; Ar = -1; 8 7 6 9 Ar 4 3 2 5 1 6 -1 8 7 -1 9 Ar 4 3 2 5 1 6