Area of a triangle in C++ :
In this C++ program, we will learn how to find the area of a triangle if its sides are given. We will take the sides as input from the user. This example will show you how to read user inputs in C++ and how to do mathematical calculations.
Before moving to the program, let me quickly show you the mathematical formula to calculate the triangle area.
Formula to calculate the area of a triangle :
We need the sides of a triangle to calculate its area. For example, if the sides of a triangle are s1, s2 and s3, its area is square root of s * (s - s1) * (s - s2) * (s - s3), where s = (s1 + s2 + s3)/2.
We will get the sides as inputs from the user and then the program will calculate the final area. We will also add two validation checks in the program :
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All sides should be positive.
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The sum of any two sides should be always greater than the third side.
These are basic validation check for a valid triangle. We will write different functions to do these validations.
Let’s code :
C++ program to find the area of a triangle :
#include<iostream>
#include<cmath>
using namespace std;
// 1
void isSideValid(float length){
if(length< 0){
cout<<"Error !! Please enter a valid side"<<endl;;
exit(0);
}
}
// 2
void checkAllSides(float first, float second, float third){
if(first + second <= third || first + third <= second || second + third <= first){
cout<<"Error !! Sides are not valid"<<endl;
exit(0);
}
}
int main()
{
// 3
float firstSide, secondSide, thirdSide;
float s,area;
// 4
cout<< "Enter the length of the first side : "<<endl; cin>>firstSide;
isSideValid(firstSide);
cout<< "Enter the length of the second side : "<<endl; cin>>secondSide;
isSideValid(secondSide);
cout<< "Enter the length of the third side : "<<endl; cin>>thirdSide;
isSideValid(thirdSide);
// 5
checkAllSides(firstSide,secondSide,thirdSide);
// 6
s = (firstSide + secondSide + thirdSide)/2;
// 7
area = sqrt(s * (s - firstSide) * (s - secondSide) * (s - thirdSide));
cout << "Area of the triangle is "<<area<<endl;
return 0;
}
Explanation :
The commented numbers in the above program denote the step numbers below :
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isSideValid function is used to check if a side entered by the user is valid or not. If it is less than 0, it exits the program.
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checkAllSides function checks if the three sides entered by the user are valid or not. If not valid, it exits the program.
-
Create some floating point variables to store the sides of the triangle, s and final area of the triangle.
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Ask the user to enter the length of each side. Read the values and also check if each one is valid or not.
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Once all sides are read, use checkAllSides function to verify if the sides are valid.
-
Calculate the value of s.
-
Calculate the area and print this value.
Sample Output :
Enter the length of the first side :
5
Enter the length of the second side :
4
Enter the length of the third side :
3
Area of the triangle is 6
Enter the length of the first side :
10
Enter the length of the second side :
12
Enter the length of the third side :
13
Area of the triangle is 56.9951