Arrays - Intro to Computer Programming - Lecture Slides, Slides of Computer Engineering and Programming

Download Arrays - Intro to Computer Programming - Lecture Slides and more Slides Computer Engineering and Programming in PDF only on Docsity!

Arrays

Lecture 11

What Is an Array?

• An array is a group of items of the same type under one variable name. It is an ordered list of elements where each is of the same data type.
• As an example, the days of the week can be represented as a one-dimensional array named day where Sunday is the first element, Monday the second, and so on.

Thinking About Arrays

• The days of the month can be thought of as a

two-dimensional array. Looking at a calendar,

each row represents a week (which can be

represented as a one-dimensional array), and

the entire month is composed of an array of

arrays, that is, a two-dimensional array.

Arrays

• Taking the concept further, the days of the

year can be represented as a three-

dimensional array, that is, an array of arrays of

arrays. The first dimension is the day of the

week, the second the week of the month, and

the third the month of the year.

Assigning Values to Arrays

• Once an array is declared, the elements are accessed by specifying the array name and the number of the element. In C, the first element is number 0, so a seven element array would have elements numbered 0 through 6.
• For the week of February 6th through the 12th, the array could be assigned as follows: day[0]=6; day[1]=7; day[2]=8; day[3]=9; day[4]=10; day[5]=11; day[6]=12;
• The number in the brackets is called an index (or a subscript).

Assigning Values to Arrays

• Optionally, the array can have values assigned to its elements when the array is declared.
• For example, the statement:

int day[ 7 ] = {6, 7, 8, 9, 10, 11, 12} ; declares a seven element array day and initializes (assigns values to) all seven of the elements.

• The program on the next slide illustrates how that works.

Program Output of an Array

• When this program is run, it will produce the following output:

day[0] is February 6, 2005 day[1] is February 7, 2005 day[2] is February 8, 2005 day[3] is February 9, 2005 day[4] is February 10, 2005 day[5] is February 11, 2005 day[6] is February 12, 2005

Another Program Example

/* Program to generate an array of 10 random numbers / #include <stdio.h> #include <stdlib.h> #define SIZE 10 / SIZE defined as symbolic constant */ int main ( ) { int i, numbers [SIZE] ; for (i = 0 ; i < SIZE ; i++ ) { numbers[ i ] = rand ( ) ; printf ( "The number[ %d ] is %d \n", i, numbers[ i ]) ; } }

APPROACH

• Read in data from file and sum the values as

read.

• Compute the average
• Use a 2nd^ loop to compute the sum of the

values – average square.

• Divide by n-
• Take square root
• You now have s, the standard deviation!!!
  • SMILEY FACE!