CS1010 AY20/21 S1 Lecture 3

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# Lecture 3

### 23 August 2021

Admin Matters<br>
Unit 5: **First C Program**<br>
Unit 6: **CS1010 I/O Library**<br>
Unit 7: **Arithmetic Operations**<br>

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## Reminders

- Tutorial/lab start this week
- 1st Catch-up this Saturday 10am
- 1st Assignment out next week
- Ungraded Exercise 0 release this Thursday

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### Before Lab
- GitHub account _must_ be ready 
- You _must_ be able to login to PE nodes

### Before Tutorial
- Attempt Problem 1.1 to 1.3

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### Catch-Up Session

- Q and A format
- Ask via [PigeonHole](https://pigeonhole.at/SEEASTENTEN) (`SEEASTENTEN`)
- Optional session for those falling behind
- No new materials will be covered

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### The Teaching Team

- 2 full-time tutors
- 3 Ph.D. part-time tutors
- 30 UG tutors
- 1:7 ratio

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

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

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### _Don't:_ do it alone

### _Do:_ Discuss with classmates and teaching team

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# Let's C

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

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

int main()
{
  int hypotenuse_square;

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

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

int hypotenuse_square; // 🙅

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

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

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.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);
}
```
]

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

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

- We will only use `double` in CS1010.

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

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.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);
}
```
]

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### Basic operators

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

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### Pitfalls: order of operations can be confusing

`8 / 2 * (2 + 2)`

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### CS1010: Use parenthesis everywhere

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

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

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

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```C 
x = x + 1;
x += 1;
```
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```C
x <op>= y;
x = x <op> y;
```
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```C 
x = x + 1;
x += 1;
x++;
++x;
```

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

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

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

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

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### _Don't_: Stop at understanding the notes

### _Do_: "play" with it, ask "what if..", "why..", "why not..", etc

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.tiny[
Version: 1.0

Last Updated: Mon Aug 23 00:44:28 +08 2021
]