CS1010 AY21/22 S1 Lecture 1

# CS1010
## Programming Methodology 
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# Lecture 1

### 9 August 2021

Admin Matters 
Unit 1: **What is a Program?** 
Unit 2: **Computational Problems and Algorithms**

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# Ooi Wei Tsang

### ooiwt@comp.nus.edu.sg

### Office Hour : Tuesday 4 - 5 PM

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## What will you learn?

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- Comfortable with reading and developing small programs to solve a given problem

- Become proficient with C and associated programming tools (`vim`, `clang`, etc)

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## What do you need to know before CS1010?

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- Comfortable with using a computer

- Comfortable with secondary school mathematics and notations

- Nothing about programming

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## Weekly Activities

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Day | Activities
:------------------|:-------------------------- 
  Mon              | Attend lecture
  Mon - Wed        | Review; problem set; quiz
  Wed              | Attend tutorial
  Thu              | Attend lab 
  Thu - Tue        | Programming assignment; exercsies

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### Tutorial and lab sessions

- start in Week **3**
- online options for those on LOA / overseas

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### Tutorial

- problem set will be discussed

- 20 students per group

- lead by a student tutor

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### Lab

- programming assignment will be discussed

- hands-on practice

- 10 students per group

- lead by a student tutor

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### Lab/Tutorial Registration

- Please manage through ModReg
- If you need to talk to a human, check with
	- Enzio Kam [`dcsekhh@nus.edu.sg`](mailto:dcsekhh@nus.edu.sg)
	- Foo Yong Qi [`dcsyqf@nus.edu.sg`](mailto:dcsyqf@nus.edu.sg)

- Module instructors do not have access to the system

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### Online Lab/Tutorial Policy

- Online attendance applies to students stranded overseas/SHN/QO/LOA  
- Online tutorial: Wednesday 6 - 7 PM
- Online lab: Thursday 6 - 8 PM

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- **Category I**: Cannot attend F2F session in Weeks 3-4 only
   - Preallocated: no action needed
   - Not Preallocated: bid for a F2F slot as usual
   - Attend online version during Week 3-4

- **Category II**: Cannot attend F2F session Weeks 3-5 (at least)
	- Preallocated: drop pre-allocated slot
	- Not Preallocated: nothing to drop
	- Attend online version for the rest of the semester

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### [Register as Online Student Here](https://luminus.nus.edu.sg/modules/600de8e9-67ec-47dd-b597-a2eeadb45792/survey/16f85196-1749-4638-9cb9-82f111c1a449)

Only for those with valid reasons (e.g., cannot enter Singapore at all or early enough)

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## "Catch-Up" Sessions

- About every three weeks

- Saturday 10 AM - 12 PM, online

- Q&A format

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## Important Resources

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## Module Homepage

[`https://nus-cs1010.github.io/2122-s1/`](https://nus-cs1010.github.io/2122-s1/)

lecture notes 
problem sets 
exercises 
assignments 
guides and manuals 
readings

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## Piazza

[`https://piazza.com/nus.edu.sg/fall2021/cs1010/home`](https://piazza.com/nus.edu.sg/fall2021/cs1010/home)

online forum 
announcements 
contact the teaching team

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## GitHub

assignment submissions 
assignment grading

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## LumiNUS

quizzes 
grades 
survey 
etc.

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# Assessments

(or, how you will be graded)

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.smaller[
Assessment         | Date                       | Time
:------------------|:-------------------------- |:-------------
Midterm | Mon, 27 Sep| 12 - 2 PM
Final | Tue, 25 Nov| 5 - 7 PM
Practical Exam 1   | Sat, 2 Oct| 9 AM - 12 PM
Practical Exam 2   | Sat, 6 Nov| 9 AM - 12 PM
]

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## Open Book Exam

### Bring any (analog) materials you want

### Nothing to memorize

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## Not "bell-curved"

- Your grade is based solely on your marks
- Not relative to others in the class.

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## Plagiarism and Cheating

- "No mercy" policy in dealing with cases
- Not worth it to cheat/copy

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## Things To Do

- Read about other policies
- Get your accounts ready

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## Office Hour Tomorrow

If you have issues with your login, pop by my office hours (AS6 05-14 or [Zoom](https://piazza.com/class/krfo8m0yrkv6t2?cid=8))

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# Words of Advice

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## "Difficult"
## "High Workload"

(but also "fun", "learned a lot")

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## Expected workload
## 10 hours/week

But your mileage may vary

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## Learning in NUS SoC is different from your experience

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### Less rote learning
### More open-ended problems
### A lot more self-learning

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### Cannot "study" programming / problem solving

### Need to actually _do it_

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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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### _Don't:_ do it alone

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

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### _Don't:_ Optimize for CAP and grades

### _Do:_ Optimize for skills, knowledge, and experience

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### _Don't:_ Do enough to get things done

### _Do:_ Invest time to master the tools

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

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### _Don't:_ focus on meeting assignment deadline

### _Do:_ think long term (your career)

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- No matter how well you have done to get here
- No matter what you know about programming

### This is a fresh start

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# Lecture 1

### 9 August 2021

Admin Matters 
Unit 1: **What is a Program?** 
Unit 2: **Computational Problems and Algorithms**

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## What is a program?
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### A sequence of step-by-step instructions given to computers to process data in order to perform a certain task.
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### How CPU Executes a Program

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## Machine Code

- Instructions that can be interpreted by a CPU

- Different CPU architecture may use different instruction sets

`1001010001011110100010101010101000101`

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## Assembly Language

- Use mnemonic to represent the instructions such as `incr`, `decr`, `store`, etc. in a more human-readable way.

- Still difficult to write: operation that is conceptually simple still requires multiple instructions to be issued.

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## Higher-Level Language

- Allow programmers to express an operation closer to their intention

- E.g., $x = x + y$ if $y < 0$

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## Higher-Level Languages

- FORTRAN (first popular programming language from 1950s)

- C (1972, still influential today)

- Many many others

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## Compilation

A compiler _compiles_ a program written in high-level language to machine code.

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# What you will learn?

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### How a C program behaves

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### How to write C programs
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### Tools and techniques to write good and correct C programs
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### How to use C to solve computational problems
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### Easy: write a program that does what you want

### Difficult: Knowing what should your program do

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## What is a computational problem?

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### Computational problems are

- problems that can be solved _step-by-step_ by a computer

- have _well-defined_ inputs, outputs, and constraints

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## Is 1933091 prime?

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## Is there a route from a Point A to Point B?

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## Find a route from Point A to Point B.

(search problem)

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## How many different routes are there from Point A to Point B?

(counting problem)
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## Find the shortest route from Point A to Point B.

(optimization problem)
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## What is the meaning of life?

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## Do I look good in this outfit?

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### Computational problem are

- problems that can be solved _step-by-step_ by a computer

- have _well-defined_ inputs, outputs, and constraints

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### Find the maximum among these numbers

```
5  9  8
1  3  2
```

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### Find the maximum among these numbers

.tiny[
```
12  20  11  20  14  2   24  36  43  16  27  6   11  7 
10  15  38  10  22  7   16  26  32  30  11  9   30  6 
20  6   27  19  26  10  27  6   19  34  5   9   3   22
10  4   13  1   10  22  43  36  39  29  41  12  13  25
17  8   30  31  29  38  2   42  7   45  24  33  9   40
34  29  37  2   26  17  19  34  6   7   34  22  21  41
38  5   15  13  9   1   42  39  5   29  38  4   22  29
41  10  26  32  30  26  16  16  18  22  32  34  14  10
5   17  25  16  19  6   31  16  3   13  8   42  41  0 
13  30  44  1   41  14  5   39  40  38  6   37  38  9 
.

```
]

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### How to Solve It?

- Scan the integers one-by-one

- Keep track of the "max so far"

- When we are done scanning, the "max so far" will be the answer.

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### Problem Formulation

- Input: $L$ = $\langle l\_0,...,l\_{k-1\} \rangle$

- Output: $m$

- Constraint $m \in L$ and $m \ge l_i$ for all $i$.

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### Scan One-By-One

- $l_i$ : The number being scanned

- $i = 0, 1, \ldots k-1$

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### "Maximum So Far"

- $m$ : max so far

- $m = l_0$ initially

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### Keeping track

- Compare $m$ with $l\_i$

- if $m < l\_i$, then update $m$ with the value of $l\_i$.

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### Done scanning?

- When we have scanned $l\_{k-1}$

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### The steps to solve a computational problem form the _algorithm_

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## Flowchart

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![:scale 75%](figures/max-flowchart-dark/max-flowchart-dark.001.png)

.smaller.center[
$k$ | $i$ | $l\_i$ | $m$ 
:---|:----|--------|-----
    |     |        |  
    |     |        |  
    |     |        |  
    |     |        |    
]

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### Variables

- $i$, $m$, $k$ are _variables_
- They have corresponding location in the memory and hold a _value_
- You can _read_ a value from a variable
- You can _write_ a value to a variable

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### Assignment

- We can assign the value of a variable to a constant (e.g., set $i$ to 1)
- or to the value of another variable (e.g., set $m$ to $l_i$).

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### Comparison

- We can compare the values of two variables
- E.g., $i$ equals $k$?  $l\_i > m$?

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### Arithmetic Operations

- We can perform arithmetic operations 
- E.g., we set $i$ to $i + 1$

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### Does this algorithm always correctly find the maximum value?

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### Correctness

- If an algorithm produces the correct output for one instance of input, it is not necessary correct

- To be correct, it has to produce the correct output _for all possible_ inputs!

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### How to check for correctness?

- Carefully choose a set of test cases to try
- Argue formally about the properties of the algorithms
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### Homework

- Post-Lecture Diagnostic Quiz
  - Due Wednesday 2359
  - You have unlimited attempts
- Problem Set 1.1 to 1.3 
  - Not graded.  To be discussed Week 3.
- Read the policies
- Setup accounts