How to Declare Array in C: Syntax and Examples

In C, you declare an array using the syntax type name[size]; where type is the data type, name is the array's name, and size is the number of elements. For example, int numbers[5]; declares an integer array with 5 elements.

Syntax

An array declaration in C has three parts:

• type: The data type of the elements (e.g., int, char).
• name: The identifier you choose for the array.
• size: The number of elements the array will hold, written inside square brackets.

The general form is: type name[size];

c

int numbers[5];
char letters[10];
float prices[3];

Example

This example shows how to declare an integer array, assign values, and print them using a loop.

c

#include <stdio.h>

int main() {
    int numbers[5];
    
    // Assign values to the array
    for (int i = 0; i < 5; i++) {
        numbers[i] = (i + 1) * 10;
    }

    // Print the array elements
    for (int i = 0; i < 5; i++) {
        printf("numbers[%d] = %d\n", i, numbers[i]);
    }

    return 0;
}

Output

numbers[0] = 10
numbers[1] = 20
numbers[2] = 30
numbers[3] = 40
numbers[4] = 50

Common Pitfalls

Common mistakes when declaring arrays in C include:

• Forgetting to specify the size (except when initializing immediately).
• Using a size of zero or negative numbers (not allowed).
• Accessing elements outside the declared size (causes undefined behavior).
• Confusing array declaration with pointer declaration.

Example of wrong and right declaration:

c

// Wrong: size missing
// int arr[]; // Error: size required without initialization

// Right: size specified
int arr[3];

// Or initialize with size inferred
int arr2[] = {1, 2, 3};

Quick Reference

Concept	Example	Notes
Declare int array of 5	int arr[5];	Creates array with 5 integers
Declare char array	char name[10];	Can hold 10 characters
Initialize array	int nums[3] = {1, 2, 3};	Size inferred if omitted
Access element	arr[0] = 10;	Index starts at 0
Invalid size	int bad[-1];	Negative size not allowed

Key Takeaways

Declare arrays with type name[size]; specifying data type and size.

Array size must be a positive integer and known at compile time.

Access array elements using zero-based indexing from 0 to size-1.

You can initialize arrays at declaration to avoid specifying size explicitly.

Avoid accessing elements outside the declared size to prevent errors.