Apr 24th 2014

Coding 101 14

Thrown A For Loop

We learn about for loops, if then statements, and get modded before Dale Chase gives us the lowdown on using external data.
Although the show is no longer in production, you can enjoy episodes from the TWiT Archives.
Guests: Dale Chase
Category: Help & How To

Welcome to Coding 101 - It's the TWiT show that gives YOU the knowledge to live in the wonderful world of the programmer. This week we are introducing our newest module, Python with Code Warrior Dale Chase!

To see all the code used in today's episode, go to Our Github Repository for Module 2

Loops (Recap)

• As we may recall, loops are an easy way to reuse code.
• It allows us to "loop" a section of code so that it doesn't have to be writen over and over.

For Loops

For Loops use a "range" function to determine the start and the end of the loop.

Code Sample:

for counter in range(0,3):

- print counter

• Notice how the counter print statement ran from 0 - 2 and NOT 0 - 3. That's because the counter is incremented at the end of each loop and each loop does a pre-test. After the code prints "2", 1 is added to the counter. When it loops back to the range function, the counter is "3" - Since we told the loop to rune as long as we are "in range" of 0 to 3", it will no longer run. (it's the same as "<" in C#)

if/else statements

• A "if" statement evaluates an relational expression and executes a block of code if that expression is true.

Code Sample:

a = raw_input("Please enter a whole number:")

b = raw_input("Please enter a second whole number:")

if a < b:

print "a is less than b"

• A "if/else" statement evaluates a relational expression and executes a block of code if that expression is true, AND EXECUTES A DIFFERENT BLOCK OF CODE IF THAT EXPRESSION IS FALSE

Code Sample:

a = raw_input("Please enter a whole number:")

b = raw_input("Please enter a second whole number:")

if a < b:

- print "a is less than b"

elif a == b:

- print "a is equal to b"

else:

- print "b is less than a"

The Modulo (Mod) Operator

• It does a division calculator and returns the remainder of that division
• Syntax: "a%b"
• Which means, "Divide a by b, and return the value of the remainder of that division"

Sample Problem

• Find a way to decide if a user-inputed number is odd or even!
• If we wanted to know if a number is odd or even, we would use the Mod operator on a value, dividing it by 2 and checking to see what number is returned as the remainder:
• If the number is "0", then we know the number was EVEN because dividing by 2 left no remainder
• If the number is "1", then we know that the number was ODD because dividing ANY odd number would leave a remainder of 1.

Sample Code:

var1 = raw_input("Please enter a whole number:")

leftover = int(var1) % 2

if leftover == 0:

- print var1, "is an even number"

else:

- print var1, "is an odd number"

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