C++ code for area of triangle, compiling but not working

[redherring1001]

This program is to find the area of a triangle using three vertices. I have used Heron's formula to do this. The program compiles but I get these warnings in the main function:

37:21: warning: variable 'aTriangle' set but not used [-Wunused-but-set-variable]
45:7: warning: 'area' is used uninitialized in this function [-Wuninitialized]

I get the first one at the struct triangle aTriangle declaration and the second at cout area. The output of the program is 0. I don't understand why.

//-----Include required headers here-----
#include<iostream>
#include<cmath>
using namespace std;
//-----End of headers-----


//-----Don't change/delete structs-----
struct vertex{
   float x;
   float y;
};


struct triangle{
    vertex vertices[3];
};
//-----Structs end here




//-----Add new functions here(if any)-----


//-----New functions end here-----


float cal_area(triangle aTriangle) {
    //Write your solution below this line
    float s,area,a,b,c;
    a=sqrt(pow((aTriangle.vertices[1].x-aTriangle.vertices[2].x),2)-pow((aTriangle.vertices[1].y-aTriangle.vertices[2].y),2));
    b=sqrt(pow((aTriangle.vertices[2].x-aTriangle.vertices[3].x),2)-pow((aTriangle.vertices[2].y-aTriangle.vertices[3].y),2));
    c=sqrt(pow((aTriangle.vertices[1].x-aTriangle.vertices[3].x),2)-pow((aTriangle.vertices[1].y-aTriangle.vertices[3].y),2));
    s=0.5*(a+b+c);
    area=sqrt(s*(s-a)*(s-b)*(s-c));
    return (area);
    //Dont write below this line
}
int main()
{ float area;
    struct triangle aTriangle;
    aTriangle.vertices[1].x=1;
    aTriangle.vertices[2].x=2;
    aTriangle.vertices[3].x=5;
    aTriangle.vertices[1].y=4;
    aTriangle.vertices[2].y=5;
    aTriangle.vertices[3].y=20;
    float cal_area(triangle aTriangle);
cout<<area<<endl;
    return 0;
}

[liuyang]

line 49, you're not actually calling the function.
Try change it to:
area = calc_area(aTriangle);