## program solution

#include <stdio.h>
#include <stdlib.h>

/* A utility function to calculate area of triangle formed by (x1, y1), (x2, y2) and (x3, y3) */
float area(int x1, int y1, int x2, int y2, int x3, int y3)

return abs((x1*(y2-y3) + x2*(y3-y1)+ x3*(y1-y2))/2.0);

/* A function to check whether point P(x, y) lies inside the triangle formed by A(x1, y1), B(x2, y2) and C(x3, y3) */
_Bool isInside(int x1, int y1, int x2, int y2, int x3, int y3, int x, int y)

/* Calculate area of triangle ABC */
float A = area (x1, y1, x2, y2, x3, y3);

/* Calculate area of triangle PBC */
float A1 = area (x, y, x2, y2, x3, y3);

/* Calculate area of triangle PAC */
float A2 = area (x1, y1, x, y, x3, y3);

/* Calculate area of triangle PAB */
float A3 = area (x1, y1, x2, y2, x, y);

/* Check if sum of A1, A2 and A3 is same as A */
return (A == A1 + A2 + A3);

/* Driver program to test above function */
int main()

/* Let us check whether the point P(10, 15) lies inside the triangle formed by A(0, 0), B(20, 0) and C(10, 30) */
if (isInside(0, 0, 20, 0, 10, 30, 10, 15))
printf ("Inside");
else
printf ("Not Inside");

return 0;

Inside