class: big, middle

# Engineering 1020: Introduction to Programming

.title[
  .lecture[Lecture 5:]
  .title[Organization and control Flow]
  
  
]

.footer[[/lecture/5/](/lecture/5/)]

---

# Python scripts

```python
# Copyright (c) 2020 Jonathan Anderson
# Permission is granted to copy and modify this code for any purpose.
#
# This is an example of a simple Python script for questing.

# First, gather some basic information from the user.
name = input('What is your name? ')
quest = input('What is your quest? ')
v = input('What is the average airspeed of an unladen swallow? ')

# Greet the brave dame or knight.
print(f'Greetings, brave {name}!')

# Convert speed into a floating-point number and calculate quest time.
v = float(v)
print(f'Your quest for {quest} will be aided when the swallow flies 792 m.')
print(f'This should take {792 / v} s.')
```

???

What can we see in this file (which is available as [quest.py](quest.py))?

* comments
* copyright
* type conversion
* variables

---

# What we just saw

### Comments

\# Helpful descriptive text
--
 for **people**, not the computer!

\# Everything from `#` to the end of the line

### Copyright

* writing code is a _creative act_
--

* more like an English assignment than Math!

---

# Organizing your writing

### How would you organize:

* a text?
--

* a letter?
--

* an essay?
--

* a report?
--

* a book?

---

# Organizing Python

| Writing text &nbsp;&nbsp; | Writing code |
|--------------|--------------|

--
| phrases | expressions |

--
| sentences | statements |

???

So far we've only seen two kinds of statements:
the **expression statement** and the **assignment statement**.
As we progress through the course, however, we'll learn about more.

--
| paragraphs | functions |

???

We've used functions in this course, but we haven't written our own yet.
That will change.

--
| chapters and parts | modules |

???

We've also used modules: `engi1020` and `math` are examples.
Towards the end of the course, we'll also see how to _create_ modules.

---

# Aside: valid names

### What _is_ a valid name?

.center[
What sorts of names have we seen thus far?
]

.floatleft[
### Python 2:

* letters, numbers and underscores
* don't start with a number
]

### Python 3:

Adds **some** Unicode characters (full details available at
[PEP 3131](https://www.python.org/dev/peps/pep-3131))

???

### Examples of valid Python 3 identifiers:

**Chinese:** 你好 (Mandarin ni hao, Cantonese lai hao)

**Hindi:** नमस्ते (namaste)

**Bengali:** হ্যালো (Hyālō)

**Urdu:** ہیلو (helo)

**Arabic:** مرحبا (mar haban)

**Hebrew:** שלום (shalom)

### Invalid identifiers:

---

# You are here

### Where in the world?

### Where in my program's execution?

### So far:

* one statement at a time
--

* a **straight line** through a script

???

Trace through execution of Monty Python Python script

---

# Example: an epic quest

### _Sequential_ control flow

???

Using sequential control flow, we can make a computer execute our instructions
far, far faster than we ever could.
That's pretty cool, but... is that all we can do?

### ... but is that all we can do?

---

# Algorithms

### Previous definition:

> step-by-step procedure **with decisions**

#### Decisions within procedures:

* is the cake golden brown?
--

* is the lug nut loose?
--

* is the error within acceptable tolerances?

---

# Flowchart

Visual representation of a procedure
--

(imperative knowledge,
--

**like code**)

### Boxes represent _activities_

### Diamonds represent _decisions_

You can trace the **flow** of logic through the procedure with your finger
--
... _digitally_
--

&nbsp;😁

???

### _Control flow_ vs _data flow_

---
class: big

.center[
<img src="https://www.ibiblio.org/apollo/Documents/GeminiCatchUpAndRendezvousAnalysisAndSimulationReport4-58-59.png"
     alt="An algorithm programmed in the Gemini computer" width="900"/>
]

---

# A little more recently:

.center[
<img src="MissionStateDiagram.png"
     alt="State diagram for the Killick-1 CubeSat" width="900"/>
]

---

# Promotion decisions

### Term 3+: _is your promotion average greater than 60%?_

### Actually, it's a little more complicated than that...

---
class: big

.center[
<img src="../flowcharts/term-3.png" width="850" alt="Term 3 promotion decisions"/>
]

---

# Flowcharts

### Exercise (just for fun):

> Draw a flowchart!

### Any process that has:

* decisions
 * actions

### _Explain_ it to someone

???

This exercise doesn't need to be submitted

---

# Control flow in programming

### Conditional control flow

> either do this or else do that, based on a _condition_

### Looping

> do this over and over, as long as a _condition_ is satisified

---

# Control flow in Python

### Conditional control flow:

```python
if condition:
	do stuff
elif another and condition:
    do other stuff
else:
	do some other stuff
```

### Looping: later!

### Note
--
 new _keywords_
--
 and indentation

---

# Example: a possibly-epic quest

.center[
<img src="../flowcharts/if-knights.png"
     alt="A flowchart for not-so-brave knights" height="450"/>
]

---

# More Pythonesque?

.center[
<img src="../flowcharts/if-knights-python.png"
     alt="A flowchart using more Python-like syntax" height="450"/>
]

---

# Exercise&ast;

.footnote[
&ast; Just for fun, not for submission
]

### Make [quest.py](quest.py) use conditional control flow

### Use this logic, or...

* What if the knight has a particularly awesome name?
* What if the swallow can't travel the necessary distance in time?

---

# Exercises

.floatleft[
### In Gradescope:

| n | Topic        | Description |
|---|--------------|-------------|
| 0 | Expressions  | 42 |
| 1 | Expressions  | Cantilever beam |
| 2 | Variables    | Age |
| 3 | Conditionals | EOPA |
]

.floatright[
### On your own:

* Flowchart
* Noble quest
]

---
class: big, middle

(here endeth the lesson)