Computer Programming | Education

C Programming | Arrays

All the basics of Arrays in C programming language.

Arrays in C | Notes

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Basic Concept

Many applications require multiple data items that have common characteristics.

In mathematics, we often express such groups of data items in indexed form: X1, X2, X3, …, Xn

Why are arrays essential for some applications?

Take an example: Finding the minimum of a set of numbers.

From 3 numbers:

if ((a <= b) && (a <= c)) 
   min = a; 
      if(b <= c) 
         min = b; 
         min = c;

From 4 numbers:

if((a <= b) && (a <= c) && (a <= d)) 
   min = a; 
       if((b <= c) && (b <= d)) 
           min = b; 
          if(c <= d) 
             min = c; 
             min = d;

The Problem

  • Suppose we have 10 numbers to handle.
  • Or 20,
  • Or 100
  • How to tackle this problem?
  • Solution –> Use Arrays

Using Arrays

All the data items constituting the group share the same name.

int x[10];

Individual elements are accessed by specifying the index.

  • X is a 10 element one-dimensional array
  • The name of the array also denotes the starting address of the array in memory.


int x[10];

  • x[0], x[1], x[2],… indicates the contents of the successive array locations.
  • x indicates the starting address in memory for the array.

Example through code:

   int x[10]; 
   x[0] = 15; 
   x[1] = x[0] + 5; 
   printf(”\n%d %d %d %u \n”, x[0], x[1], x[2], x); 


15 20 1107384350 3221224640 
// 1107384350 Garbage Value
// 3221224640 Address

Declaring Arrays

Like variables, the arrays that are used in a program must be declared before they are used.

General syntax:

type array-name[size];

  • type specifies the data type of element that will be contained in the array (int, float, char, etc.).
  • size is an integer constant which indicates the maximum number of elements that can be stored inside the array.

Example: int marks[5];

  • marks is an array containing a maximum of 5 integers.

Examples :

  • int x[10];
  • char line[80];
  • float points[150];
  • char name[35]

If we are not sure of the exact size of the array, we can define an array of a large size. int marks[50]; .

Though in a particular run we may only be using, say, 10 elements.

How an array is stored in memory?

Starting from a given memory location, the successive array elements are allocated space in consecutive memory locations

x : starting address of the array in memory

k : number of bytes allocated per array element

Element a[i] :: allocated memory location at address x+i*k.

First array index assumed to start at zero.

Accessing Array Elements

A particular element of the array can be accessed by specifying two things:

  1. Name of the array.
  2. Index (relative position) of the element in the array.

In C, the index of an array starts from zero.


An array is defined as int x[10];

The first element of the array x can be accessed as x[0], fourth element as x[3], tenth element as x[9], etc.

The array index must evaluate to an integer between 0 and n-1 where n is the number of elements in the array.

Any integer expression can be given as the index.

  1. a[x+2] = 25;
  2. b[3*x-y] = a[10-x] + 5;

A Warning

In C, while accessing array elements, array bounds are not checked


int marks[5]; 
marks[8] = 75;

The above assignment would not necessarily cause an error.

Rather, it may result in unpredictable program results.

Initialization of Arrays

General form

type array_name[size] = {list of values};


int  marks[5] = {72, 83, 65, 80, 76}; 
char name[4] = {’A’, ’m’, ’i’, ’t’}; 

Some special cases

If the number of values in the list is less than the number of elements, the remaining elements are automatically set to zero.

float total[5] = {24.2, -12.5, 35.1}; 

total[0]=24.2, total[1]=-12.5, total[2]=35.1, total[3]=0, total[4]=0

The size may be omitted. In such cases the compiler automatically allocates enough space for all initialized elements.

int  flag[] = {1, 1, 1, 0}; 
char name[] = {’A’, ’m’, ’i’, ’t’};

Find the minimum of a set of 10 numbers

   int  a[10], i, min; 
   for(i=0; i<10; i++) 
      scanf(”%d”, &a[i]); 
   min = 99999;    /* or, min=a[0] */ 
   for(i=0; i<10; i++){ 
      if(a[i] < min) 
         min = a[i]; 
   printf(”\n Minimum is %d”, min); 

#Alternate Version 1

change only one line to change the problem size

#define size 10 
// change here
   int a[size], i, min; 
   for(i=0; i<size; i++) 
      scanf("%d”, &a[i]); 
   min = 99999; 
   for(i=0; i<size; i++){ 
      if(a[i] < min) 
         min = a[i]; 
   printf(”\n Minimum is %d”, min); 

#Alternate Version 2

Define an array of large size and use only the required number of elements

   int a[100], i, min,n; 
   // number of elements
   for(i=0; i<n; i++) 
      scanf("%d”, &a[i]); 
   min = 99999; 
   for(i=0; i<n; i++){ 
      if(a[i] < min) 
         min = a[i]; 
   printf(”\n Minimum is %d”, min); 

Computing gpa

Handling two arrays at the same time

#define  nsub  6 
   int grade_pt[nsub],cred[nsub],i,gp_sum=0,cred_sum=0; 
   float gpa; 
   for(i=0; i<nsub; i++) 
      scanf(”%d %d”, &grade_pt[i],&cred[i]); 
   for(i=0; i<nsub; i++){ 
      gp_sum += grade_pt[i] * cred[i]; 
      cred_sum += cred[i]; 
   gpa = (float) gp_sum / cred_sum; 
   printf(”\n GPA is: %f”, gpa); 

Things you cannot do

You cannot

  • use “=” to assign one array variable to another:
a = b;  /* a and b are arrays */ 
  • use “==” to directly compare array variables:
if (a == b)  ……… 
  • directly scanf or printf arrays:
printf (”……”, a);

How to copy the elements of one array to another?

By copying individual elements:

int a[25], b[25]; 
for (j=0; j<25; j++) 
   a[j] = b[j];

How to read the elements of an array?

By reading them one element at a time.

int a[25]; 
for(j=0; j<25; j++) 
   scanf (”%f”, &a[j]); 
  • The ampersand (&) is necessary.
  • The elements can be entered all in one line or in different lines.

How to print the elements of an array?

By printing them one element at a time.

  • The elements are printed one per line.
for (j=0; j<25; j++) 
   printf (”\n %f”, a[j]); 
  • The elements are printed all in one line (starting with a new line).
printf (”\n”); 
   for (j=0; j<25; j++) 
      printf (” %f”, a[j]); 

If you are new to the C Programming and if you are willing to explore it, then you must visit our previous articles on C Programming.

  1. C Programming | String Functions
  2. C Programming | Character Strings

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