gistfile1.txt

#pragma once
#include "ofMain.h"

class testApp : public ofBaseApp{
 public:
  int randomCounts[20];
  void setup();
  void update();
  void draw();
};

gistfile2.txt

#include "testApp.h"
#include <ofGraphics.h>

void testApp::setup(){
  ofBackground(255);
  ofSetColor(0);
}

void testApp::update(){
  int index = ofRandom(20);
  randomCounts[index]++;
}

void testApp::draw(){
  int w = ofGetWidth() / 20;
  for (int x = 0; x < 20; ++x) {
    ofRect(x * w, ofGetHeight() - randomCounts[x], w - 1, randomCounts[x]);
  }
}

main.cpp

#include "ofMain.h"
#include "testApp.h"

int main( ){
  ofSetupOpenGL(1024,768,OF_WINDOW);
  ofRunApp(new testApp());
}