nchy13 0 Light Poster

HI, I am trying to set the consecutive pixels to a specific color so as to obtain a line. Though, I know there is a built in function for drawing the line, but I am interested to do it without using any GL primitive.
This is the display function as of now. Here I thought that changing limits from -250 to 250 instead of -1.0 to 1.0 will do the job but to no avail.
In this code I am just getting a point a the centre of the window.
Any help is appreciated as to how make a line using pixels.
Here both height and width of window is 501 pixels.

void renderFunction()
    glClearColor(0.0, 0.0, 0.0, 0.0);
    glColor3f(1.0, 1.0, 1.0);
    glOrtho(-250.0, 250.0, -250.0, 250.0, 0.0, 0.0);
        for(int i=1; i<100; i++)
            glVertex2f(float(i/250), float(i/250));