class: big, middle

# Engineering 1020: Introduction to Programming

.title[
  .lecture[Lecture 6:]
  .title[If statements]
  
  
]

.footer[[/lecture/6/](/lecture/6/)]

---

# Last time

### 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

---

# Flowchart: promotion decisions

.center[
<img src="../flowcharts/term-3.png" width="600" alt="Term 3 promotion decisions"/>
]

---

# Control flow in Python

### Conditional control flow:

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

### Note new _keywords_ and indentation

???

A condition is either true or false:
it's an expression that evaluates to a Boolean value.

---

# Exercise&ast;

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

### Make [python.py](../6/python.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?

---

# Example

## Critical buckling stress

$$
F_{cr} =
\begin{cases}
(0.658) ^ {\lambda_c^2} F_y     & \lambda_c \leq 1.5 \cr
\frac{0.877}{\lambda_c^2} F_y   & \lambda_c > 1.5
\end{cases}
$$

???

In structural engineering, the Critical Buckling Stress for a column
can be determined using this equation in the
Load and Resistance Factor Design method,
in which $ \lambda\_c $ is the _slenderness ratio_, a measure of how
slender the column is, and $ F\_y $ is the _yield force_ at which
the column's material will fail.

---

# An academic example

> Convert a numeric mark into a letter grade

### Note: _operator chaining_

???

Python allows us to combine comparators together like a mathematical
_range_ ($3 < x < 5$).

---

# A musical exercise

> Write a script that prompts for one input, a year from 1958 onwards,
  and prints out the "top" or "best" song of that year's decade
  (use [this list](https://en.wikipedia.org/wiki/List_of_Billboard_Hot_100_chart_achievements_by_decade#Songs_by_total_weeks_at_number_one) if helpful).

---
class: big, middle

(here endeth the lesson)