This lesson you will learn:

• The use of one dimensional arrays
• The difference between strings and characters

Q. What's the difference between a blonde and an ironing board ?
A. Occasionally you have trouble getting the legs apart on an ironing board.

    Arrays are a data structure which hold multiple variables of the same data types. Consider the case where a programmer needs to keep track of a number of people within an organization. So far, our initial attempt will be to create a specific variable for each use. This might look like:

    int name1 = 101;
    int name2 = 232;
    int name3 = 231;

It becomes increasingly more difficult to keep track of this as the number of variables increase. Arrays offer a solution to this problem. An array is a multi-element box, a bit like a filing cabinet, and uses an indexing system to find each variable stored within it. In C, indexing starts at zero.

Arrays, like other variables in C, must be declared before they can be used. The replacement of the above example using arrays looks like this:

int names[3];
names[0] = 101;
names[1] = 232;
names[2] = 231;
names[3] = 0;

We created an array called names, which has space for four integer variables. You may also see that we stored 0 in the last space of the array. This is a common technique to signify the end of an array. Arrays have the following syntax, using square brackets to access each indexed value (called an element).

    x[i];

So that x[5] refers to the sixth element of an array called x. In C, an array elements start with 0. Assigning values to array elements is done by:

    x[10] = g;

And assigning array elements to a variable is done by:

    g = x[10];

In the following example, a character based array named work is declared, and each element is assigned a character. The last element is filled with a zero value, to signify the end of the character string (in C, there is no string type, so character based arrays are used to hold strings). A printf statement is then used to print out all the elements of the array.

Example 1:

/* Introducing arrays, 2 */

#include <stdio.h>

int main(void)
{

char work[20];

word[0] = ‘H’;
word[1] = ‘e’;
word[2] = ‘l’;
word[3] = ‘l’;
word[4] = ‘o’;
word[5] = 0;

printf(“The contents of word[] is -? %s\n”, word);

return 0;

   }

Sample program output:

The contents of word[] is Hello

Accepting single characters from the keyboard

getchar()

The following program illustrates this:

#include <stdio.h>

int main(void)
{

int I;
int ch;

for (I = 1; i<=5; ++i)
{
    ch = getchar();
    putchar();
}

return 0;

}

Sample program output

AACCddEEtt

The program reads five character (one for each iteration of the for loop) from the keyboard. Note that getchar() gets a single character from the keyboard, and putchar() writes a single character (in this case, ch) to the console screen.

Reading Strings

#include <stdio.h>

int main(void)
{

char name[25];
printf("Input a character string, up to 25 characters. \n");
gets(name):
printf("The string is %s\n", name);
printf("End of program.\n");

return 0;

}

gets collects a string of characters terminated by a new line from the standard input stream and puts it into name. It replaces the new line by a null character (\0) in name; it also allows input strings to contain certain characters (spaces, tabs).

A sample program showing the advantage of using an array (float)

#include <stdio.h>

int main(void)
{

float wageWk1, wageWk2, wageW3....... 47 more variables ..... wageWk51, wageWk52;
printf("\nEnter the wage for week 1")
scanf("%f", &wageWk1);

printf("\nEnter the wage for week 2");
scanf("%f", &wageWk2);

........... NINTEY-FOUR MORE LINES OF CODE

printf("\nEnter the wage for week 51");
scanf("%f", &wageWk51);

printf("\nEnter the wage for week 52");
scanf("%f", &wageWk52);

return 0;

}

Use of an Array

#include <stdio.h

int main(void)
{

float wageWk[52];
int cntr, numofwks;

printf("\nHow many weeks of wages do you want to enter?");
scanf("%d", &numofwks);

cntr=0;
while (cntr <numofwks && cntr <52)
{
    printf("\nEnter the wages for week %d>), cntr+1);
    scanf("%f", &wageWk[cntr]);
    cntr = cntr+1;
}

return 0;

}

back to top          exercise      lesson 6       lesson 8