> I'm trying to do a shape of star.

Start by drawing out several examples on graph paper.

The point of the exercise is to find the patterns between the size of the star

Code:

printf ("Enter size (10-20)\n");
scanf (" %d", &s);

and what the final shape is.

Say you wanted to draw a triangle of height 6 (h=6)

Code:

.....*
....***
...*****
..*******
.*********
***********

So there are a couple of things to notice

- the number of leading spaces counts down one for each successive row.

- the number of stars increases by two for each successive row.

Code:

for ( row = 0 ; row < h ; row++ ) {
leading_spaces = h - row - 1;
num_stars = row * 2 + 1;
}