move rect on vector

//http://youtube.com/user/thecplusplusguy
//move rect on vector
#include <iostream>
#include <SDL/SDL.h>
#include <cmath>


void calculateVector(float sx,float sy,float ex,float ey,float& vecx,float& vecy)
{
    //a direction vector: end_point-start_point
    vecx=ex-sx;
    vecy=ey-sy;
    //calculate the length with the help of pythagorean theorem
    float length=sqrt(vecx*vecx+vecy*vecy); //might be std::sqrt
    if(length!=0.0)
    {
        //and normalize the vector
        vecx/=length;
        vecy/=length;
    }
}


int main(int argc,char** argv)
{
    float curX=30,curY=40;  //The current position of the rect. I use float, so we don't loose precision, for example imagine
    //if the speed is 0.5 So I add do curX+=0.5  which is just curX, because it casted to an int, with float, we don't have such a problem.
    int endX=30,endY=40;    //this can stay an int, because this is just the end coordinate
    float vecx=0.0,vecy=0.0;    //The vector, because it will be between 0.0 and 1.0, definitely have to be a float, this is the 2 separate
    //component of a 2D vector, if you want to use vectors often, create a class for them
    float speed=3.0; //3 pixel/s
    calculateVector(curX,curY,endX,endY,vecx,vecy); //calculate the direction vector
    SDL_Surface* screen=SDL_SetVideoMode(640,480,32,SDL_SWSURFACE);
    SDL_Event event;
    Uint32 start;
    bool running=true;
    while(running)
    {
        start=SDL_GetTicks();
        while(SDL_PollEvent(&event))
        {
            if(event.type==SDL_QUIT)
                running=false;
            else if(event.type==SDL_MOUSEBUTTONDOWN)
            {
                //if we clicked somewhere, calculate the new direction vector with the new end coordinate
                endX=event.button.x;
                endY=event.button.y;
                calculateVector(curX,curY,endX,endY,vecx,vecy);
            }
        }

        //if we are close enough, just place make the current coordinate to the end coordinate (so we don't have to add lengthed vectors)
        if(abs(curX-(float)endX)<5 && abs(curY-(float)endY)<5)  //might be std::abs
        {
            curX=endX;
            curY=endY;
        }else{
            //else do the vector operation, and move on that direction
            curX+=speed*vecx;
            curY+=speed*vecy;
        }
        SDL_Rect rec;
        rec.x=curX;
        rec.y=curY;
        rec.w=20;
        rec.h=20;

        SDL_FillRect(screen,0,0); //clear screen

        SDL_FillRect(screen,&rec,SDL_MapRGB(screen->format,255,0,0));   //draw the rect on the screen

        SDL_Flip(screen);
        if(1000.0/30.0>(SDL_GetTicks()-start))
            SDL_Delay(1000.0/30.0-(SDL_GetTicks()-start));
    }
}