4.6 Nested decisions

Learning objectives

By the end of this section you should be able to

• Describe the execution paths of programs with nested if-else statements.
• Implement a program with nested if-else statements.

Nested decision statements

Suppose a programmer is writing a program that reads in a game ID and player count and prints whether the user has the right number of players for the game.

The programmer may start with:

if game == 1 and players < 2:
  print("Not enough players")
if game == 1 and players > 4:
  print("Too many players")
if game == 1 and (2 <= players <= 4):
  print("Ready to start")
if game == 2 and players < 3:
  print("Not enough players")
if game == 2 and players > 6:
  print("Too many players")
if game == 2 and (3 <= players <= 6):
  print("Ready to start")

The programmer realizes the code is redundant. What if the programmer could decide the game ID first and then make a decision about players? Nesting allows a decision statement to be inside another decision statement, and is indicated by an indentation level.

An improved program:

if game == 1:
  if players < 2:
    print("Not enough players")
  elif players > 4:
    print("Too many players")
  else:
    print("Ready to start")
if game == 2:
  if players < 3:
    print("Not enough players")
  elif players > 6:
    print("Too many players")
  else:
    print("Ready to start")
# Test game IDs 3-end