C/C++ :: Create Image And Output It As PPM File

I have an assignment where I have to create an image and output it as a .ppm file. It has to have a black background and have some letters in a different color. My professor told me that my .ppm header should have p3 600 300 255 and P6 600 300 255(what this means, think it sets up the width x height which should be 300 x 600).

This is what I have so far:

#include <iostream>
#include <fstream>
using namespace std;
int main() {
struct pixel {
unsigned char red;

[Code] ....

Problem in first for loop and what it should look like inside of the for loop, after that I should be able to figure this out... with the fstream (how to output the results in a .ppm file).