C Program to find the area of a triangle with three sides

April 18, 2022, Learn eTutorial

Here we are explaining how to write a C program to find the area of a triangle with three sides using heron's formula. For a better understanding of this C program example, we always recommend you to learn the basic topics of C programming listed below:

How to find the area of a triangle

The area of a Triangle is the region that comes inside the three sides of the triangle that makes a closed shape.

Triangles can be classified into different types by following shapes and properties, important among them are the Equilateral triangle, Isosceles triangle, Right-angled Triangle.

In this C program, we are considering a normal Triangle with three different length sides and the length of each side is known for finding its Area. We are using Heron's formula to find such a triangle's area.

find area of a circle with given radius

Heron's formula can be applied in this C program using two different steps, which are

  1. First, we have to find the perimeter "s" of the triangle which can be found by adding the length of three sides of the triangle.
  2. Second, we have to apply that perimeter value 's' in the Herons formula with the sides of the triangle to find the area.
  3. s = (a+b+c)/2
  4. pythagorean triples in a range

where a,b,c are the three sides of the triangle and 's' is the perimeter.

How area calculation of triangle implemented in C Program

  • We are defining each variable using the int datatype and taking the user's input to get the Triangle's sides' values using the printf and scanf function defined in the standard libraries.
  • Now we have to compute the value of perimeter 's' by adding the sides of the triangle and dividing it by 2.
  • Finally, apply the value of perimeter 's' in the heron's formula to find the area of the triangle using sqrt function and print the result. 


STEP 1: Include the header files used in C programming to use some built-in functions inside the program such as stdio.h, conio.h, math.h

STEP 2: Open the main() to start the program, C program execution starts with the main()

STEP 3: Accept the Sides of the Triangle from the user using printf and scanf built-in functions and store the values in Variables. 

STEP 4: Calculate the value of S using the formula a+b+c /2

STEP 5: Calculate the area using the formula sqrt[s(s-a)*(s-b)*(s-c)] and assigned to variable area

STEP 6: Using the printf method print the value of the area in C programming. 

C Source Code

                                          #include <stdio.h>
#include <math.h>

void main() {
  int s, a, b, c, area; // defines the variables.
  printf("Enter the values of a,b and c\n");
  scanf("%d %d %d", & a, & b, & c);

  /* compute s*/

  s = (a + b + c) / 2;
  area = sqrt(s * (s - a) * (s - b) * (s - c));
  printf("Area of a triangle = %d\n", area);


Enter the values of a,b and c

Area of a triangle = 6