Arrays: One Dimensional

Lecture 11

Arrays

In this lecture we will get familiar with one of the C’s most essential data structures called arrays. Arrays are data structures consisting of related data items of the same type. You can also say that it is a group of memory locations related by the fact that they all have the same name and same type.

Why Arrays

For understanding the arrays properly, let us consider the following program:

No doubt, this program will print the value of x as 10. Why so? Because when a value 10 is assigned to x, the earlier value of x, i.e. 5, is lost. Thus, ordinary variables (the ones which we have used so far) are capable of holding only one value at a time (as in the above example). However, there are situations in which we would want to store more than one value at a time in a single variable.

For example, suppose we wish to arrange the percentage marks obtained by 100 students in ascending order. In such a case we have two options to store these marks in memory:

1.    Construct 100 variables to store percentage marks obtained by 100 different students, i.e. each variable containing one student’s marks.

2.    Construct one variable (called array or subscripted variable) capable of storing or holding all the hundred values.

Obviously, the second alternative is better. A simple reason for this is, it would be much easier to handle one variable than handling 100 different variables. Moreover, there are certain logics that cannot be dealt with, without the use of an array

One Dimensional Array

In C, a one dimensional array is a list of variables that are all of the same type and accessed through a common name. An individual element in an array is called array element. Array is helpful to handle a group of similar types of data.

To declare a one dimensional array, we use-

data_type array_name [size];

Here, data_type is a valid C data type, array_name is the name of tha array and follows the convention of naming a variable, and size specifies the number of elements in the array.

int my_array[20];

-Declares an array name my_array of type integer that contains 20 elements.

An array element is accessed by indexing the array using the number of element. In C, all arrays begin at zero. This means that if you want to access the first element in an array, use zero for the index. To index an array, specify the index of the element you want inside square brackets. The second element of my_array will be-

my_array [1]

To assign an array element a value, put the array on the left side of the assignment operator. The example gives the first element of my_array the value 200.

my_array [0]=200;

C stores one dimensional array in one contiguous memory location with first element at the lower address. For example, an array named a of 10 elements can occupy the memory as follows-

Index	Value
a [0]	-45
a [1]	10
a [2]	32
a [3]	100
a [4]	9
a [5]	9
a [6]	50
a [7]	100
a [8]	-9
a [9]	12

Now, let us consider a program that declares an array of 10 elements and initializes every element of that array with 0.

main(){

      int a[10], i;

      for (i=0;i<10;i++)

            a [i] = 0;

      printf (“Element \t Value”);

      for (i=0;i<10;i++)

            printf (“%d \t%d”, i, a [i]  );

}

The elements of an array can also be initialized by following the declaration with an equal sign and a comma separated list of values within a pair of curly brace.

main(){

      int a[10]={1,2,3,4,5,6,7,8,9,10},

      int i;

      printf (“Element \t Value”);

      for (i=0;i<10;i++)

            printf (“%d \t%d”, i, a [i]  );

}

If there are fewer values than elements in array, the remaining elements are initialized automatically with zero.

main(){

      int a[10]={1,2,3,4,5,6,7,8,9},

      int i;

      printf (“Element \t Value”);

      for (i=0;i<10;i++)

            printf (“%d \t%d”, i, a [i]  );

}

If you put more values than the array can hold, there will be a syntax error-

main(){

      int a[5]={1,2,3,4,5,6,7,8,9,10},

      int i;

      printf (“Element \t Value”);

      for (i=0;i<10;i++)

            printf (“%d \t%d”, i, a [i]  );

}

If array size is omitted during declaration, the number of values during array initialization will be the number of elements the array can hold. For example, the following array will automatically have space for 5 elements.

main(){

      int a[]={1,2,3,4,5},

      int i;

      printf (“Element \t Value”);

      for (i=0;i<10;i++)

            printf (“%d \t%d”, i, a [i]  );

}

A Simple Program Using Array

The following program declares an array to hold the marks of 30 students. Firstly, the program with the help of a loop takes marks of 30 students inside the array. Then, again with the help of another loop, the program calculates their total marks. Finally, it delivers the average mark by dividing the total mark by number students (30)-

Character Arrays

Character arrays have several unique features. A character array can be initialized using a string literal.

char string1[ ] = “first”;

-this declaration initialized the elements of array string1 to the individual characters in the string literal “first”. The size of array string1 is determined by the compilers based on the string.

Note- “first” string literal contains five characters plus a special string termination character called null character (\0). Thus, string1 array actually has 6 elements-f, i, r, s, t and \0. A character array representing a string should always have declared large enough to hold the number of characters in the string plus the terminating null character.

Character arrays can be initialized as follows as well-

char string1 [ ]= {‘f’, ‘i’, ‘r’, ‘s’, ‘t’, ‘\0’};

This is because string is really an array of characters. We can access individual characters in a string directly using array subscript notation. For example, string1 [3] is the character ‘s’.

We can also input a string directly from the keyboard using scanf () function and %s specifier.

char string1 [20];

scanf (“%s”, string1);

Note- the name of the array is passed to scanf () without the preceding & used with other variables. The & is normally used to provide scanf () with a variable’s location in a memory so a value can be stored there. Array name is the address of the start of the array, therefore, & is not necessary.

Note- scanf () reads characters from the keyboard until the first whitespace character is encountered- it does not care how large the array is. scanf () takes upto the first whitespace.

main(){

      char string1 [20], string2 [ ] = “Hello There”;

      int i;

      printf (“Enter a string with white spaces: ”);

      scanf (“%s”, string1);

      printf (“\nString 2 is %s”, string2);

      printf (\n String 1 is );

      for (i=0;string1 [i]!=’\0’;i++)

            printf (“%c”, string1 [i]);

}

The output of the program is-

Enter a string with white spaces: Hello There

String 2 is Hello There

String 1 is Hello