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C++ Program to Find Area, Perimeter of Triangle



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In this article, you will learn and get code on area and perimeter of triangle in C++ programming. There are many approaches used here to find area and perimeter of a triangle. Here are the list:

What to Do before Program ?

Before starting the program, if you are not aware about triangle types and its related formula, then you can refer to Area & Perimeter of Triangle Formula for all the neccessary details.

Area of Triangle with Base & Heigth

This program finds area of a triangle based on its base and height value. The question is, write a program in C++ to find area of a triangle with base and height entered by user at run-time. Here is its answer.

// C++ Program to Find Area of Triangle with Base and Height
// ----codescracker.com----

#include<iostream>
using namespace std;
int main()
{
    float b, h, area;
    cout<<"Enter Base length of Triangle: ";
    cin>>b;
    cout<<"Enter Heigth length of Triangle: ";
    cin>>h;
    area = 0.5*b*h;
    cout<<"\nArea = "<<area;
    cout<<endl;
    return 0;
}

This program was build and run under Code::Blocks IDE. Here is its sample run:

c++ area of triangle

Now enter the value of base and height of triangle to find and print its area as shown in the output given below:

area of triangle in c++

Area of Triangle with Three Sides (Heron's Formula)

This program uses Heron's Formula to calculates area of a triangle. Heron's formula is used when length of all the three sides are given:

// Area of Triangle with Three Sides (Heron's Formula)
// ----codescracker.com----

#include<iostream>
#include<cmath>
using namespace std;
int main()
{
    float a, b, c, s, area;
    cout<<"Enter Length of Three Sides (one by one): ";
    cin>>a>>b>>c;
    s = (a+b+c)/2;
    area = sqrt(s*(s-a)*(s-b)*(s-c));
    cout<<"\nArea = "<<area;
    cout<<endl;
    return 0;
}

Here is its sample run with user input 5, 4, 3 as values of three sides of triangle:

c++ program area of triangle

Note - The function sqrt() returns the square root of value passed as its argument. For example, sqrt(25) returns 5. This function is defined in cmath header file.

Perimeter of Triangle with 3 Sides

Now let's create a program to find the perimeter of a triangle using values of its three sides given by user at run-time:

// Find Perimeter of Triangle using 3 Sides
// ----codescracker.com----

#include<iostream>
using namespace std;
int main()
{
    float a, b, c, per;
    cout<<"Enter Length of First Side: ";
    cin>>a;
    cout<<"Enter Length of Second Side: ";
    cin>>b;
    cout<<"Enter Length of Third Side: ";
    cin>>c;
    per = a+b+c;
    cout<<"\nPerimeter = "<<per;
    cout<<endl;
    return 0;
}

Here is the initial snapshot of sample run:

c++ perimeter of triangle

Now supply the length of all three sides of triangle say 5, 4, 3 and then press ENTER key to see the following output:

perimeter of triangle c++

Perimeter of Triangle based on User's Choice

Here is another program on calculating the perimeter of a triangle. This is a menu-driven program, that provides user, 4 options to perfom the task according to his/her choice:

// Find Perimeter of Triangle Based on User's Choice
// ----codescracker.com----

#include<iostream>
using namespace std;
int main()
{
    float a, b, c, per;
    int ch;
    do
    {
        cout<<"1. Equilateral Triangle\n";
        cout<<"2. Isosceles Triangle\n";
        cout<<"3. Scalene Triangle\n";
        cout<<"4. Exit\n";
        cout<<"\nEnter Your Choice: ";
        cin>>ch;
        switch(ch)
        {
            case 1:
                cout<<"\nEnter Side Length: ";
                cin>>a;
                per = 3*a;
                break;
            case 2:
                cout<<"\nEnter First Length (of Equal Sides): ";
                cin>>a;
                cout<<"Enter Second Length: ";
                cin>>b;
                per = 2*a+b;
                break;
            case 3:
                cout<<"\nEnter Length of all 3 Sides: ";
                cin>>a>>b>>c;
                per = a+b+c;
                break;
            case 4:
                break;
            default:
                cout<<"\nWrong Choice!";
                continue;
        }
        if(ch>=1 && ch<=3)
            cout<<"\nPerimeter = "<<per<<"\n\n";
    }while(ch>=1 && ch<=3);
    cout<<endl;
    return 0;
}

Here is its sample run:

find perimeter of triangle c++

Now provide your choice according to the following information:

Now, if you have a triangle whose two sides are of same length, then press 2 as your choice, and enter the first length (the length of side that has another duplicate side of same length) and then enter the second length of triangle. Press ENTER key to see its perimeter as output.

After printing the perimeter, it will again display the menu to choose and operate for another triangle or for same triangle with different length until and unless you press 4 to exit from it.

perimeter of triangle in c++ program

Area & Perimeter of Triangle using Function

This program finds both area and perimeter of a triangle using a user-defined function. Here area and perimeter gets calculated based on 3 sides input:

// Area and Perimeter of Triangle using Function
// ----codescracker.com----

#include<iostream>
#include<cmath>
using namespace std;
float areaOfTriagle(float, float, float);
float perOfTriangle(float, float, float);
int main()
{
    float a, b, c, area, per;
    cout<<"Enter Length of all Three Sides: ";
    cin>>a>>b>>c;
    area = areaOfTriagle(a, b, c);
    cout<<"\nArea = "<<area;
    per = perOfTriangle(a, b, c);
    cout<<"\nPerimeter = "<<per;
    cout<<endl;
    return 0;
}
float areaOfTriagle(float a, float b, float c)
{
    float s, ar;
    s = (a+b+c)/2;
    ar = sqrt(s*(s-a)*(s-b)*(s-c));
    return ar;
}
float perOfTriangle(float a, float b, float c)
{
    return (a+b+c);
}

The sample run of above program is given below:

c++ area perimeter triangle using function

Area & Perimeter of Triangle using Class

This program uses class and object, to find and print area and perimeter of a triangle with three sides:

// Find Area and Perimeter of Triangle using Class
// ----codescracker.com----

#include<iostream>
#include<cmath>
using namespace std;
class CodesCracker
{
    private:
        float a, b, c, s, ar;
    public:
        void getData();
        float areaOfTriagle();
        float perOfTriangle();
};
void CodesCracker::getData()
{
    cout<<"Enter Length of all Three Sides: ";
    cin>>a>>b>>c;
}
float CodesCracker::areaOfTriagle()
{
    s = (a+b+c)/2;
    ar = sqrt(s*(s-a)*(s-b)*(s-c));
    return ar;
}
float CodesCracker::perOfTriangle()
{
    return (a+b+c);
}
int main()
{
    CodesCracker c;
    float area, perimeter;
    c.getData();
    area = c.areaOfTriagle();
    cout<<"\nArea = "<<area;
    perimeter = c.perOfTriangle();
    cout<<"\nPerimeter = "<<perimeter;
    cout<<endl;
    return 0;
}

It will produce the same output as of previous program. To learn more about class and object, you can follow the separate tutorial on it.


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