C Program to Find Area of Rectangle

To find the area of a rectangle in C, use area = length * width; where length and width are the rectangle's sides.

Examples

Inputlength = 5, width = 3

OutputArea of rectangle: 15

Inputlength = 10, width = 7

OutputArea of rectangle: 70

Inputlength = 0, width = 4

OutputArea of rectangle: 0

How to Think About It

To find the area of a rectangle, multiply its length by its width. This is like finding how many square units fit inside the shape by counting rows and columns.

Algorithm

1

Get the length of the rectangle from the user

2

Get the width of the rectangle from the user

3

Multiply length by width to calculate the area

4

Display the calculated area

Code

c

#include <stdio.h>

int main() {
    int length, width, area;
    printf("Enter length: ");
    scanf("%d", &length);
    printf("Enter width: ");
    scanf("%d", &width);
    area = length * width;
    printf("Area of rectangle: %d\n", area);
    return 0;
}

Output

Enter length: 5
Enter width: 3
Area of rectangle: 15

Dry Run

Let's trace the example where length = 5 and width = 3 through the code

1

Input length

User enters 5, so length = 5

2

Input width

User enters 3, so width = 3

3

Calculate area

area = length * width = 5 * 3 = 15

4

Print area

Output displayed: Area of rectangle: 15

Step	Variable	Value
1	length	5
2	width	3
3	area	15

Why This Works

Step 1: Getting inputs

We ask the user to enter the length and width using scanf to store values in variables.

Step 2: Calculating area

We multiply length and width using * operator to find the area.

Step 3: Displaying result

We print the area using printf so the user sees the answer.

Alternative Approaches

Using float for decimal inputs

c

#include <stdio.h>

int main() {
    float length, width, area;
    printf("Enter length: ");
    scanf("%f", &length);
    printf("Enter width: ");
    scanf("%f", &width);
    area = length * width;
    printf("Area of rectangle: %.2f\n", area);
    return 0;
}

This allows decimal values for length and width, useful for more precise measurements.

Using functions to calculate area

c

#include <stdio.h>

float calculateArea(int l, int w) {
    return l * w;
}

int main() {
    int length, width;
    printf("Enter length: ");
    scanf("%d", &length);
    printf("Enter width: ");
    scanf("%d", &width);
    float area = calculateArea(length, width);
    printf("Area of rectangle: %.0f\n", area);
    return 0;
}

Separates calculation into a function for cleaner code and reusability.

Complexity: O(1) time, O(1) space

Time Complexity

The program performs a fixed number of operations regardless of input size, so it runs in constant time O(1).

Space Complexity

Only a few variables are used to store inputs and output, so space complexity is O(1).

Which Approach is Fastest?

All approaches run in constant time; using functions adds clarity but no significant speed difference.

Approach	Time	Space	Best For
Basic integer multiplication	O(1)	O(1)	Simple integer inputs
Float inputs for decimals	O(1)	O(1)	Precise measurements with decimals
Function-based calculation	O(1)	O(1)	Code clarity and reuse