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)
background(0)
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:
stroke(255)
line(i, 80, i, height / 2)
else:
stroke(153)
line(i, 20, i, 180)