2. Conditional Expressions

Conditional Expressions - If/Else Statements

If Statement

if <condition>:
    <code>
<back to flow>

Side note - Indentation in python

Indentation is mandatory for the interpreter in order to understand the workflow.

If/Else Statements

if <condition>:
    <code>
else:
    <other code>
<back to flow>

If/elif/Else Statements

if <condition>:
    <code>
elif <condition>:
    <code>
else:
    <other code>
<back to flow>

Multiple if Statements

if <condition>:
    <code>
if <condition>:
    <code>
else:
    <other code>
<back to flow>

Nested if Statements

if <condition>:
    <code>
    if <condition>:
        <code>
    else:
        <other code>
else:
    <other code>
    if <condition>:
        <code>
    else:
        <other code>
<back to flow>

Pass Statement

if <condition>:
    Pass
if <condition>:
    <code>
else:
    <other code>
<more code>

One-liners

Inline Ifs

if <condition>: <statement_1>; <statement_2>; ...; <statement_n>

Conditional Expressions

a = <expr1> if <condition> else <expr2>
#Example:
n = 1 if 1<2 else 2
# now n is 1
n = 1 if 1>2 else 2
# now n is 2

More info.

Exercise

1. Prompt user for a number between 0-100. Tell them they won the game if they choose less then 29. Lost it otherwise. Assume the input is really between 1-100.
2. Prompt user for an integer > 0. This number defines a spectrum. Ask the user to guess a number within the spectrum. They win iff they are in the bottom 10 percent of the spectrum or in the top 10. Anything in between - they lose. Assume the input is valid.
3. Following #2 - before you play they game, check if the 2nd number is within the spectrum. If not, tell them we don't play if they try to cheat.
4. Following #3 - Make sure the users give proper integers before starting the game.
5. Following #4 - Lets give losers a 2nd chance. If they can guess the spectrum's average we'll let them win anyway but only in the condition they guess a valid integer.
6. Following #5 - Here's a list of ID's: 59, 61, 67, 71, 73, 79, 83, 89, 97. Those people have tried to cheat us before. Before playing the game, ask the users for their name and ID. If the ID is not valid (valid IDs are 2 digit numbers) or, if this user tried to cheat us before (we assume they can't give a fake ID) - kick them out! If all is "Kosher" - greet them by their name and start the game.
7. Write a tax calculator. We'll make an example of a differential taxing system common in the world (a similar system is used in Israel). If a worker's monthly salary is up to 100, there is no tax. if the salary is up to 1000, the first 100 is free of tax and the rest is taxed 10%. if the salary is up to 10000, the first 100 is free of tax, the rest up to 1000 is taxed 10% and the rest is taxed 20%. if the salary is up to 100000, the first 100 is free of tax, the rest up to 1000 is taxed 10%, the rest up to 10000 is taxed 20% and the rest is taxed 30%. Every earnings larger then 100000 are taxed 50%. Prompt the users for their monthly salary and print out the tax they have to pay and the NET salary. These kinds of programs are used in the real world.