write a c program to check line segment intersection. we have already discussed the line segment intersection theory on our previous post  http://wikistack.com/line-segment-intersection/. Now we know how to make a generic line equation ax+ by = c from given line segment.

To check whether two line segments intersect or not

• From given line segment , extract generic line equation A1x + B1y = C1, where A1,B and C1 define the line. How to get A1,B1 and C1 from given line segment , has been discussed at http://wikistack.com/line-segment-intersection/
• If the two lines are not parallel , they will intersect somewhere else. Say it is (x,y).
• It is obvious that intersection point would be common for both the lines.
• Check whether intersection point (x,y) is on both the line segments, or not.

### cpp program to check line segment intersection

Let us assume we have been given two line segment AB (0,2 2,0) and CD (0,0,2,2). Another input is EF(1,-3,2,-2)  and GH(3,-1,4,-2). The below program will check whether AB and CD intersect or not and same as for EF and GH.