[allwiyn]

hi,
How to write a function that checks if the circle passes through four given points.

plz give me the logic or concept for making this function.

[seeguna]

It is better to go thru some circle clipping algorithms for better implementation

[oleber]

Calculate the center of the circle (probably you have it ).

And calculate the distance of this points to the center. Mathematics

[listendinesh]

If you have radius and center cordinates then you can use the standred equation of circle.

((X- H)*(X -H)) + ((Y -K)*(Y - K)) = R*R


H -> center x cordinate
K -> center y cordinate
R -> Radius

X -> x cordinate of given point
Y -> y cordinate of given point

Make a function which take two arguments ( given point x and y cordinate) and return a bool flag ( true if circle passes through given point otherwise false).
In function
calculate X -H and get its sqrt
(Given point X - Center Point X)
calculate Y -K and get its sqrt
add both result and compare with radius square
if both equal the and get its sqrt

Note :
1 : Please take care of floating point issues
2 : This is for one point you can extend for more points
3 : make a struct for point , that would be a good candidate like

struct point
{
int x,
int y
};