# Concept: loops ## The for loop The for-loop repeats -simplified- a command n times: ### Example The following loop is executed 5 times: ``` python for i in range(5): print("I'm in a loop!") ``` The program gives the following output ``` I'm in a loop! I'm in a loop! I'm in a loop! I'm in a loop! I'm in a loop! ``` ## The counter variable You can use the variable i as a counter variable. It counts up (starting from 0): ### Example ``` python for i in range(5): print(i) ``` The program gives the following output ``` 0 1 2 3 4 ``` ## General form: Generally written: ``` python for i in range(max): ``` or ``` python for i in range(min, max): ``` You can specify how many times the loop will be run or specify specific ranges: ### Examples: Drawing with loops You can draw with loops: ``` python from miniworldmaker import * board = Board(200, 200) for i in range(4): Circle((20 + 50 * i, 50), 20) board.run() ``` ### Checkerboard pattern With the module operator you can check if a result is divisible by 2, namely ``x divisible by 2 exactly if x % 2 == 0` This can be used to draw chessboard-like patterns by combining loops with an if query: ``` python from miniworldmaker import * board = Board(200, 50) for i in range(4): rect = Rectangle((50 * i, 0), 50, 50) if i % 2 == 0: rect.color = (255,0,0, 255) else: rect.color = (255, 255, 255, 255) board.run() ``` ### Graphs Graphs can also be drawn in this way: ``` python from miniworldmaker import * board = Board(400, 400) for x in range(400): gl = 0.5*x + 50 y = 400 - gl Point((x, y)) board.run() ``` ### Nested loops You can use nested loops to draw multidimensional patterns. ``` python from miniworldmaker import * board = Board(200, 200) for i in range(4): for j in range(4): Circle((20 + 50 * i, 20 + 50 * j), 20) board.run() ```