C Programming Arrays

In this article, you will learn to work with arrays. You will learn to declare, initialize and, access array elements with the help of examples.
C arrays

An array is a collection of data that holds fixed number of values of same type. For example: if you want to store marks of 100 students, you can create an array for it.

float marks[100];

The size and type of arrays cannot be changed after its declaration.

Arrays are of two types:

  1. One-dimensional arrays
  2. Multidimensional arrays (will be discussed in next chapter)

How to declare an array in C?

data_type array_name[array_size];

For example,

float mark[5];

Here, we declared an array, mark, of floating-point type and size 5. Meaning, it can hold 5 floating-point values.

Elements of an Array and How to access them?

You can access elements of an array by indices.

Suppose you declared an array mark as above. The first element is mark[0], second element is mark[1] and so on.

C Array declaration

Few key notes:

  • Arrays have 0 as the first index not 1. In this example, mark[0]
  • If the size of an array is n, to access the last element, (n-1) index is used. In this example, mark[4]
  • Suppose the starting address of mark[0] is 2120d. Then, the next address, a[1], will be 2124d, address of a[2] will be 2128d and so on. It's because the size of a float is 4 bytes.

How to initialize an array in C programming?

It's possible to initialize an array during declaration. For example,

int mark[5] = {19, 10, 8, 17, 9};

Another method to initialize array during declaration:

int mark[] = {19, 10, 8, 17, 9};


Initialize an array in C programming

Here,

mark[0] is equal to 19
mark[1] is equal to 10
mark[2] is equal to 8
mark[3] is equal to 17
mark[4] is equal to 9

How to insert and print array elements?

int mark[5] = {19, 10, 8, 17, 9}

// insert different value to third element
mark[3] = 9;

// take input from the user and insert in third element
​scanf("%d", &mark[2]);

// take input from the user and insert in (i+1)th element
scanf("%d", &mark[i]);

// print first element of an array
printf("%d", mark[0]);

// print ith element of an array
printf("%d", mark[i-1]);

Example: C Arrays

// Program to find the average of n (n < 10) numbers using arrays

#include <stdio.h>
int main()
{
     int marks[10], i, n, sum = 0, average;
     printf("Enter n: ");
     scanf("%d", &n);
     for(i=0; i<n; ++i)
     {
          printf("Enter number%d: ",i+1);
          scanf("%d", &marks[i]);
          sum += marks[i];
     }
     average = sum/n;

     printf("Average = %d", average);

     return 0;
}

Output

Enter n: 5
Enter number1: 45
Enter number2: 35
Enter number3: 38
Enter number4: 31
Enter number5: 49
Average = 39

Important thing to remember when working with C arrays

Suppose you declared an array of 10 elements. Let's say,

int testArray[10];

You can use the array members from testArray[0] to testArray[9].

If you try to access array elements outside of its bound, let's say testArray[12], the compiler may not show any error. However, this may cause unexpected output (undefined behavior).

Before going further, checkout these array articles: