What is an Array in C

Array in C programming is a collection of similar types of elements (Type may be an integer, float, long, etc.). So, in this programming language, we can’t store multiple data type values in an array.

For example, an integer array in C will store all the integer elements. If you try to insert a float or char value into that array, then the compiler will throw an error.

In our previous articles, we saw the variable declaration and initialization, and they are pretty good for regular purposes. What if we want to store 50 employees’ salaries? Is it worth creating 50 variables and assigning those values? What happens if it is 100 employees? C Programming language introduced the concept of the array to handle the issues.

Types of Array in C Programming

There are three types of arrays in C Programming:

One Dimensional
Two Dimensional
Multi-Dimensional
- Three Dimensional
- Four Dimensional etc

NOTE: In this Programming, the array of characters called strings

Syntax of an Array

The syntax of One Dimensional Array in C Programming is as follows:

Data_Type ArrName [ArrSize];

Data_type: It will decide the type of elements the array will accept. For example, If we want to store integers, then we declare the Data Type as int, If we want to store floating-point values, then we declare the Data Type as float, etc
ArrName: This is the name you want to give to it. For example, students, age, marks, employees, etc
Arr_Size: Number of elements an array can hold or store. For example, if Arr_Size =10, then it will hold 10 values.

For Example,

int Student_Age[5];

Here, we used int as the data type to declare an array in c programming. So, it will accept only integers. If you try to add float values, then it will throw an error.
Student_Age is the name.
The size of an Array is 5. It means Student_Age will only accept 5 integers.
- If we try to store more than 5, the compiler will throw an error.
- We can store less than 5. For Example, If we store 3 integer values, the remaining 2 will be assigned to the default value (Which is 0).

Initialization of Array in C programming

There are multiple ways to initialize an array, and the first approach to declaring is

int Employees[5] = {1, 2, 3, 4, 5}

Here, We initialized the array at the declaration time only.

Second Approach to Initialize

int Employees[ ] = {1, 2, 3, 4, 5}

Here, We haven’t mentioned the size. However, the compiler is intelligent enough to calculate the size of an array in C by checking the number of elements.

Third Approach to Initialize

int Employees[5] = {1, 4, 5}

Here we declared Employees with size 5, but we only assigned 3 variables. In this situation, the remaining values are assigned to default values (0 in this case).

The above-declared example will be:

Employees[5] = {1, 4, 5, 0, 0}

//It means

Employees[0] = 1

Employees[1] = 4

Employees[2] = 5

Employees[3] = 0

Employees[4] = 0

Fourth Approach of Initialization

The above 3 approaches are good for storing a small number of elements into it. What if we want to store 50, 100, or more values? It will be a nightmare to add all of them using any of the approaches mentioned above. To resolve this, we can use the loop concept along with the array.

int i, Employees[100];

for (i =0; i < 100 ; i++)
 {
   Employees[i] = i*2;
 }

Access Elements of an Array in C programming

We can access the elements of an Array using indexes. Using the index, we can access or alter/change each item present in it separately. The index value starts at 0 and ends at n-1, where n is the size.

For example, if an array stores 5 elements, the index starts at 0 and ends with 4. To access or alter the 1st value, use ArrName[0] and to access or alter the 5th value, then use ArrName[4]. Let’s see the example of t for better understanding:

int Student_Age[5] = {5, 10, 15, 20, 25};

//To Access the values in the Student_Age[5]

Printf("%d", Student_Age[0]); - It will display the First element = 5

Printf("%d", Student_Age[3]); - It will display the Fourth element = 20

//To Alter the values in the Student_Age[5]

Student_Age[2] = 56; - It will change the value of Student_Age[2] from 15 to 56

Student_Age[4] = 92; - It will change the value of Student_Age[4] from 25 to 92

The final output will be {5, 10, 56, 20, 92}

Array in C Programming Example

In this program, We will declare an integer array with a size of 10, and then we will sum those 10 values and displays the output.

#include <stdio.h>

int main()
{
 int i, Sum =0;
 int ExArr[10] = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100};
 
 for (i=0; i<10; i++)
 {
   Sum = Sum + ExArr[i];

   printf("Addition of %d to it = %d \n", ExArr[i], Sum);
 }
 
 printf("\nTotal Sum of the value in ExArr = %d \n", Sum);
 
 return 0;
}

In this example, We declared the following one

ExArr[10] = {10, 20, 30, 40, 50, 60, 70, 80, 90, 100};

ExArr[10] is an integer with size 10 (index values are 0 to 9). We assigned those 10 values at the declaration time.

for (i=0; i<10; i++) statement start the iteration at 0 and perform the iteration until it reaches nine because our index value ends at 9.

Sum= sum+ExArr[i]; statement is used to add each and individual element present in the ExArr[10]

Let us see the C array program execution in iteration wise

First Iteration : for (i = 0; i < 10; i++)
Sum = Sum + ExArr[i]
Here, i value is 0, and sum= 0. So, Sum = Sum + ExArr[0]
Sum = 0 + 10 = 10

Second Iteration: for (i = 1; 1 < 10; 1++)
Sum = Sum + ExArr[1]
Sum = 10 + 20 = 30

Third Iteration: for (i = 2; 2 < 10; 2++)
Sum= Sum + ExArr[2]
Sum = 30 + 30 = 60

Fourth Iteration of array: for (i = 3; 3 < 10; 3++)
Sum= Sum + ExArr[3]
Sum = 60 + 40 = 100

Fifth Iteration: for (i = 4; 4 < 10; 4++)
Sum= Sum+ ExArr[4] = 100 + 50 = 150

Sixth Iteration: for (i = 5; 5 < 10; 5++)
Sum= Sum+ ExArr[5] = 150 + 60 = 210

Seventh Iteration: for (i = 6; 6 < 10; 6++)
Sum= Sum+ ExArr[6]
Sum = 210 + 70 = 280

Eighth Iteration of array in c programming: for (i = 7; 7 < 10; 7++)
Sum = 280 + 80 (ExArr[7]) = 360

9^th Iteration: for (i = 8; 8 < 10; 8++)
Sum = Sum + ExArr[8] = 360 + 90 = 450

10^th Iteration: for (i = 9; 9 < 10; 9++)
Sum= Sum + ExArr[9] = 450 + 100 = 550

For the next iteration, the condition inside the for loop (10 < 10) will fail.

Things to Recall

It is always best practice to initialize the array at the declaration time. If you don’t know the values, then initialize to 0 or null.
Items in it can be accessed using an index value.
The index value starts at 0 and ends at n-1, where n is the size.