Description

Area of triangle can be calculated using Heron's formula. 
In geometry, Heron's formula gives the area of a triangle when
the length of all three sides are known. The triangle exists 
if the sum of any of its two sides is greater than the third side.

C/C++

/* C Program to calculate area of triangle */
//Save it as AreaTriangle.c

#include<stdio.h>
#include<math.h>
int main(){

    float side1, side2, side3, area, s;

    printf("Enter the sides of triangle : ");
    scanf("%f%f%f",&side1,&side2,&side3);

    // Length of sides must be positive
    //The triangle exists if the sum of any of its two sides is greater than the third side.
    if (side1<0 || side2<0 || side3<0 || (side1+side2 <= side3) || side1+side3 <=side2 || side2+side3 <=side1){
        printf("Area cannot be calculated");
    }
    else{

        //Calculate semiperimeter
        s = (side1+side2+side3)/2;

        //Calaculate area
        area = sqrt(s*(s-side1)*(s-side2)*(s-side3));

        printf("Area : %.3f",area);
    }

    return 0;
}

Input:
Enter the sides of triangle : 
3
4
5

Output:
Area : 6.000

Java

/* Java Program to calculate area of triangle */
//Save it as AreaTriangle.java

import java.io.*;
import java.util.Scanner;

public class AreaTriangle {

    public static void main(String[] args) {
        
            Scanner scanner = new Scanner(System.in);
        
            float side1, side2, side3, area, s;

        System.out.println("Enter the sides of triangle : ");
        side1 = scanner.nextFloat();
        side2 = scanner.nextFloat();
        side3 = scanner.nextFloat();

            // Length of sides must be positive
        //The triangle exists if the sum of any of its two sides is greater than the third side.
        if (side1<0 || side2<0 || side3<0 || (side1+side2 <= side3) || side1+side3 <= side2 || side2+side3 <= side1){
            System.out.println("Area cannot be calculated");
        }
            else{

                //Calculate semiperimeter
            s = (side1+side2+side3)/2;

                //Calaculate area
            area = (float) Math.sqrt(s*(s-side1)*(s-side2)*(s-side3));

            System.out.println("Area : " + area);
        }
    }
}

Input:
Enter the sides of triangle : 
3
4
5

Output:
Area : 6.0

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