Nested Loops

We’ve now seen a few ways to use loops.

for _ in range(6):
    print("Hi!")

for i in range(5, 0, -1):
    print(i)

for x in ["Hi", "Ciao", "Hola"]:
    print(x)

for c in "Go Huskies!":
    print(c)

What if we wanted to keep track of two counts at the same time? The solution is to put a for loop inside another for loop.

for i in range(1, 5):
    print(i, "Times Table")
    for j in range(1, 5):
        print(i, "x", j, "=", i * j)

Practice: Counting prints¶

How many times is “CSE 160” printed?

for i in range(2, 8, 2):
    for j in range(5):
        print("CSE 160")

Example: Pairing elements¶

Nested loops can be used to pair every department string from the outer loop with every course number from the inner loop.

for dept in ["CSE", "BIO", "INFO"]:
    for num in [180, 331, 480]:
        print(dept, num)

Example: Seeing stars¶

Outer loop variables can be accessed within the inner loop, not only to pair-up elements but even to setup the inner loop.

for i in range(5):
    line = ""
    for j in range(i):
        line += "*"
    print(line)

Practice: Seeing stars in reverse¶

Modify the preceding code snippet (repeated below) to print the rows of stars in reverse order: the last printed line should become the first one and so forth.

for i in range(5):
    line = ""
    for j in range(i):
        line += "*"
    print(line)

Practice: Dotted lines¶

Write code that uses for loops to print the output:

....1
...2.
..3..
.4...
5....