Intro to Control Structures

Control structures are programming concepts that let you control the flow of a program. The key types of control in modern software are decision-making structures and looping structures.

Decision-Making

The first decision-making mechanism we will learn is an if/then/else statement. These are very natural since the syntax matches well to our plain language. As with many languages Python uses ‘==’ for comparison, since the ‘=’ is reserved for assigning values to variables.

if name == 'John':
    print('Welcome back, John!')
else:
    print('Welcome to our site, {}'.format(name))

Looping

Looping is a common control structure that allows you to perform actions repeatedly.

For Loop

The first control function we are going to work with is a for loop. For loops can be used in many ways to loop across items:

Loop a certain number of times using the ‘in range’ syntax. This loops incrementing a counter, so printing the numbers 0 through 9:
```
 for i in range(10):
  print(str(i))
```
2) You an loop across a list of items
```
 names = ['Bob', 'John', 'Joe']
 for name in names:
  print('{}'.format(name))
```

You an loop across a list of items

names = ['Bob', 'John', 'Joe']
for name in names:
 print('{}'.format(name))

While Loop

While loops are another kind of loop. While loops loop while a condition is True. So if you want to play a game until a user gets over 100 points:

 while total_points <= 100:
     points = play_round()
     # Note the line below uses shorthand += which is the same as
     # total_points = total_points + points
     total_points += points

Exercise

To put this all together we will implement a madlib. What are the steps of building a madlib? The students should be able to frame this up independently, but something like this:

Write a story
Pull out the verbs/nouns/adjectives you want to make dynamic
Ask the user to enter those words
Print out the mad lib with the injected words
Ask the user if they want to try again