c, get distance between a point and a line (two points)

float calcDistance(float x1, float y1, float x2, float y2, float x3, float y3)

{

    float px = x2-x1;

    float py = y2-y1;

    

    float something = px*px + py*py;

    

    float u =  ((x3 - x1) * px + (y3 - y1) * py) / something;

    

    if(u > 1){

        u = 1;

    }else if(u < 0)

    {

        u = 0;

    }

    float x = x1 + u * px;

    float y = y1 + u * py;

    

    float dx = x - x3;

    float dy = y - y3;

    

    

    float dist = sqrt(dx*dx + dy*dy);

        

    return dist;

}

http://stackoverflow.com/questions/849211/shortest-distance-between-a-point-and-a-line-segment