CS1010 AY20/21 S1 Lecture 3

class: middle, center

# Lecture 3

### 24 August 2020

`vim` 
Unit 5: **First C Program** 
Unit 6: **CS1010 I/O Library** 
Unit 7: **Arithmetic Operations**

---
class: middle,center

## 工欲善其事 必先利其器

### Confucius said: To get things done properly, get the tools ready first.
---
class: middle, center

### Wei Tsang said: "Invest time to master the tools"

(e.g., `bash`, `vim`, `git`, etc)

### "Think long term gain, not just to get things done now"

---
class: middle, center

## Learn a source code editor

---
class: middle,center

### One editor for all tasks (email, notes, report, programming) for the rest of your career

---
class: middle,center

### Installed by default in many systems

---
class: middle,center

### Use one that is terminal-based

---
class: middle,center

### Avaiable on restricted exam environment for CS1010

---
class: middle,center

# `vim`

---
class: middle

### Basic Movement: `h` `j` `k` `l`
### Mode Switching: `i` `esc`
### Save and quiz: `ZZ`

---
class: middle

### For the rest, learn as you need.
### Ask: "how to do this faster?" and learn from there.

---
class: bottom,center
background-image: url(figures/dota-hotkeys.jpg)

If you can learn the hotkeys for games, you can learn the hotkeys for `vim`.

---
class: middle

### Tips: 
- Run `vimtutor`
- Read the `vim`-related readings on CS1010 website (incl Aaron's videos!)

---
class: middle

## Reminders

- Tutorials start this Thursday
- Quizzes 1-3 due this Thursday 10am
- 1st Catch-up this Saturday 10am
- 1st Assignment out next week

---
class: middle

## Before Thursday

- GitHub account _must_ be ready 
- You _must_ be able to login to PE nodes 
- Attempt Problem 1.1 to 1.3

---
class: middle

.fit[![TAs](figures/tutors/group1.png)]

---
class: middle

.fit[![TAs](figures/tutors/group2.png)]

---
class: middle,center

# Let's C

---
class: middle

```C
int square(int x) 
{
  return x * x;
}
```

---
class: middle

.tiny[
```C
int square(int x)
{
  return x * x;
}

int main()
{
  int hypotenuse_square;

hypotenuse_square = square(3) + square(4);
  return 0;
}
```
]

---
class: middle

.tiny[
```C
int square(int x)
{
  return x * x;
}

int hypotenuse_square; // 🙅

int main()
{
  hypotenuse_square = square(3) + square(4);
  return 0;
}
```
]

---
class: middle,center

.fit[![meme](figures/meme/bad-good-global.jpg)]

---
class: middle

.tiny[
```C
#include <math.h>

long square(long x)
{
  return x * x;
}

double hypotenuse_of(long base, long height)
{
  return sqrt(square(base) + square(height));
}

int main()
{
  hypotenuse_of(3, 4);
}
```
]

---
class: middle,center

- `int` is not sufficient for most CS1010 purposes.
- We will only use `long` in CS1010.

---
class: middle

.tiny.center[
type  | num of bits
-----:|:--------
`float` | 32
`double` | 64
]

- We will only use `double` in CS1010.

---
class: middle,center

.fit[![meme](figures/meme/bad-good-int-long.jpg)]

---
class: middle

.moretiny[
```C
#include <math.h>
#include "cs1010.h"

long square(long x)
{
  return x*x;
}

double hypotenuse_of(long base, long height)
{
  return sqrt(square(base) + square(height));
}

int main()
{
  double hypotenuse;
  long base = cs1010_read_long();
  long height = cs1010_read_long();
  hypotenuse = hypotenuse_of(base, height);
  cs1010_println_double(hypotenuse);
}
```
]

---
class: middle,center

### Basic operators

`+` `-` `*` `/` `%`

---
class:middle

### Pitfalls: order of operations can be confusing

`8 / 2 * (2 + 2)`

---
class:middle

### CS1010: Use parenthesis everywhere

`8 / (2 * (2 + 2))`

`(8 / 2) * (2 + 2)`

---
class: middle,center

.fit[![meme](figures/meme/bad-good-arithmetic.jpg)]

---
class:middle

```C 
x = x + 1;
x += 1;
```
---
class: middle

```C
x <op>= y;
x = x <op> y;
```
---
class: middle

```C 
x = x + 1;
x += 1;
x++;
++x;
```

---
class: middle

```C
y = x++;
```
is the same as
```C
y = x;
x = x + 1;
```

---
class: middle

```C
y = ++x;
```
is the same as
```C
x = x + 1;
y = x;
```

---
class: middle

```C
x = x++;
```

---
class:middle

```C
x = x++;
```

The behavior is not defined.  It is up to the compiler.

---
class: middle,center

.fit[![meme](figures/meme/bad-good-plusplus.jpg)]

---
class: bottom

.tiny[
Version: 1.0

Last Updated: Mon Aug 24 11:34:14 +08 2020
]