Conditions are like questions. They allow a program to decide to take one action if the answer to a question is true or to do another action if the answer to the question is false. The questions asked within a program are always logical or relational statements. For example, if the variable 'i' is equal to zero then draw a line.

size(640, 360)

for i in range(10, width, 10):
    # If 'i' divides by 20 with no remainder draw the first line
    # else draw the second line
    if i % 20 == 0:
        line(i, 80, i, height / 2)
        line(i, 20, i, 180)