Cool fire effect SDL, C++

//Implemented by http://www.youtube.com/user/thecplusplusguy
//SDL library used
//fire effect
#include <iostream>
#include <SDL/SDL.h>
using namespace std;
const int FPS=30;
const int WIDTH=640;
const int HEIGHT=480;
const float dump=0.5;
Uint32 colors[100];
float fire[HEIGHT][WIDTH];

void generateFire()
{
        for(int i=0;i<WIDTH;i++)
        {
            int ran=rand()%50;
            if(ran==0)
                fire[HEIGHT-1][i]=0;
            if(ran==1)
                fire[HEIGHT-1][i]=99;
        }
    for(int i=0;i<HEIGHT-1;i++)
        for(int j=1;j<WIDTH-1;j++)
        {
            fire[i][j]=((fire[i][j]+fire[i+1][j+1]+fire[i+1][j]+fire[i+1][j-1])/4)-dump;
            if(fire[i][j]<0)
                fire[i][j]=0;
            if(fire[i][j]>=100)
                fire[i][j]=99;
        }
}

void renderFire(SDL_Surface* screen)
{
    for(int i=0;i<HEIGHT;i++)
        for(int j=0;j<WIDTH;j++)
        {
            ((Uint32*)screen->pixels)[i*screen->pitch/4+j]=colors[(int)fire[i][j]];
        }
}

void interpolate(SDL_Surface* screen,int lindex,int hindex,int str,int stg,int stb,int endr,int endg,int endb)
{
    float stepr,stepg,stepb;
    stepr=(endr-str)/(hindex-lindex);
    stepg=(endg-stg)/(hindex-lindex);
    stepb=(endb-stb)/(hindex-lindex);
    float curr=str,curg=stg,curb=stb;
    for(int i=lindex;i<hindex;i++)
    {
        colors[i]=SDL_MapRGB(screen->format,(int)curr,(int)curg,(int)curb);
        curr+=stepr;
        curg+=stepg;
        curb+=stepb;
    }
}



int main(int argc,char** argv)
{
    SDL_Init(SDL_INIT_EVERYTHING);
    SDL_Surface* screen=SDL_SetVideoMode(WIDTH,HEIGHT,32,SDL_SWSURFACE);
    bool running=true;
    SDL_Event event;
    Uint32 start;

    colors[0]=SDL_MapRGB(screen->format,0,0,0);
    interpolate(screen,0,35, 0,0,0,255,0,0);
    interpolate(screen,34,65,255,0,0,255,160,0);
    interpolate(screen,64,100,255,160,0,255,255,255);
    for(int i=0;i<HEIGHT;i++)
        for(int j=0;j<WIDTH;j++)
            fire[i][j]=0;
    while(running)
    {
        start=SDL_GetTicks();
        while(SDL_PollEvent(&event))
        {
            switch(event.type)
            {
                case SDL_QUIT:
                    running=false;
                    break;
                case SDL_KEYDOWN:
                    switch(event.key.keysym.sym)
                    {
                        case SDLK_ESCAPE:
                            running=false;
                            break;
                    }
                    break;
            }
        }
        SDL_FillRect(screen,NULL,0);
        generateFire();
        renderFire(screen);

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