Array Variables.c

A variable array is a group of variables under the same name but with a different index value for each element in the array.  Here is an example of an array declaration and initialization:

  int p[] = {1, 2, 3, 5, 7, 11};

Each array element has a name (which is p in this example, the same as the array name) and an index (between brackets) that makes it possible to select an element.  This declaration sets aside six variables, each storing a prime number.  This array has been initialized so that the p[0] array element stores 1.  Likewise, the p[1] element stores 2.  It continues for the rest of the array elements:  p[2] stores 3, p[3] stores 5, p[4] stores 7, and p[5] stores 11.

• Use the Open Project button to Open Array Variables.side.
• Examine the code and try to predict what the SimpleIDE Terminal will display.
• Use the Run Project with Terminal button to display the programs outputs, and compare the actual results to your predicted results.

/*
 Array Variables.c
 Declare and initialize an array and display a couple of its slements.
*/

#include <stdio.h>                            // Include standard I/O header
#include "stamp.h"                            // Include stamp functions

main()                                        // Main function
{
  int p[] = {1, 2, 3, 5, 7, 11};              // Initialize the array
  pause(1000);                                // Wait 1 s for host
  printf("p[0] = %d\n", p[0]);                // Display what p[0] stores
  printf("p[3] = %d\n", p[3]);                // display what p[3] stores
}

How the Code Example Works

int p[] = {1, 2, 3, 5, 7, 11} initializes an array named p that stores prime numbers.  Keep in mind that p[0] stores 1, p[1] stores 2, p[2] stores 3, p[3] stores 5, and so on.  So, printf(“p[0] = %d\n”, p[0]) displays the contents of p[0], which is 1.  Likewise, printf(“p[3] = %d\n”, p[3]) displays the contents of p[3], which is 5.

Did You Know?

• You can declare an array with six elements, but without initializing the values,  like this: int p[6];
• You can assign the array elements later, like p[4] = 7;

Try this

Here is an example that shows how the value of an array element can be reassigned.  Take a look at the second to last statement in the main function.  It’s p[3] = 101.  After that, printf(“p[3] = %d\n”, p[3]) will allow you to verify that the new value p[3] stores is 101.

• Click the Save Project As button and save your project as Array Variable Reassignment. 
• Modify the program using the example below.  (Just add the last two lines.)
• Click the Run Project with Terminal button, and verify that the program starts with the value of [3] being 5, and that it reassigns it to 101.

Your Turn 

• Expand Array Variable Reassignment.c by adding commands to the end of the program that puts 11 in p[0], 7 in p[1], 5 in p[2], 3 in p[3], 2 in p[4], and 1 in p[5].
• Expand your program further so that it displays the values after they have been updated.