CS1010 AY20/21 S1 Lecture 6

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# Lecture 6

### 13 September 2021

.smaller[
Admin Matters<br>
Unit 13: **Call Stack**<br>
Unit 14: **Array**<br>
]
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### Assignment 2

- Due tomorrow night (23:59)
- Graded on correctness (including syntax, practices, approach, and logic), style, and efficiency.

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### Reminders

- Make sure that your submission compiles cleanly without errors or warnings.  (0 if cannot compile; -1 per warning)
- Marks will be deducted if you do not demonstrate a full understanding of what we taught so far.

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## Warning

### Plagiarism will not be tolerated.   You may discuss how to solve the assignment, but make sure you code up the solution yourself.

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### Upcoming releases:

- Exercise 5 on Arrays today
- Practical Exam I from 20/21 on Thursday
- Midterm from 20/21 later today
- Assignment 3 on Thursday
    - Grading criteria: same as Assignment 2
	- Due on 21 September

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### Reminders

- **Catch-up II**: 18 September, 2021 (Saturday) 10am
- **Midterm**: 27 September, 2021 (Monday)
- **PE I**: 2 October 2021 (Saturday)

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## Warning

### Pay attention to exam regulations.  Disciplinary actions will be taken against violators.

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### Tutorial 4

- Problem Sets 11-12

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### Lab 4

- Mock Midterm
- PE I from 20/21

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### Lab 5

- Mock PE I
- PE I from 18/19

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### Anon. Feedback on Tutors

- Please let us know how we are doing
- Constructive criticism and encouragement are both welcome
- Due This Friday

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# Call Stack

---
.cols[
.fifty[
.smaller[
```C
int main() 
{ 
  long x = 1; 
  long y; 
}
```
]
]
.fifty[

]]

---
.cols[
.fifty[
.smaller[
```C
long add(long a, long b)
{    
	long sum;    
	sum = a + b;    
	return sum;  
}

int main()
{    
	long x = 1;    
	long y;    
	y = add(x, 10);  
}
```
]
]
.fifty[

]]

---
.cols[
.fifty[
.smaller[
```C
long add(long a, long b)
{    
	long sum;    
	sum = a + b;    
	a = 42;
	return sum;  
}

int main()
{    
	long x = 1;    
	long y;    
	y = add(x, 10);  
}
```
]
]
.fifty[

]]

---
.cols[
.fifty[
.smaller[
```C
void add(long sum, long a, 
         long b)
{
  sum = a + b;
}

int main()
{
  long x = 1;
  long sum;
  add(sum, x, 10);
}
```
]
]
.fifty[

]]

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# Array

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Array is a _compound data type_ that stores multiple values of the same type

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```C
long list[10];
```

`list` is an array that stores 10 `long` values.

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```C
long list[10]; // declare
list[4] = 100; // write
```

`list[4]` refers to the 5th element in the array `list`.

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.small[
```C
long list[10] = {1, 2, 3, 1, 5, 10, 10, 4, };
```
]

Unspecified elements initialized to 0.

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### Array as Function Parameter

.smaller[
```C
long max(long list[10]) { .. }
long max(long len, long list[len]) { .. }
long max(long len, long list[]) { .. }
```
]

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### Pointers

```C
double *ptr;
long *addr;
```

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An array is stored contiguously in memory.

.fit[![array](figures/stack/stack.011.png)

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### Array Decay

```C
long list[10];
```
`list` decays into the memory address of its first element.

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.smaller[
```C
long a[2] = {0, 1};
long b[2] = {0, 1};

if (a == b) {  // always false
  :
}

b = a; // not possible
```
]

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.smaller[
```C
long max(long len, long list[len]) {
  // only pointer is passed in
}
  :
long list[10];
max(10, list);  // passing in only the pointer
```
]

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### Returning an Array

.smaller[
```C
long* square(const long len, long list[len]) {
 :
}
```
]

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### Common bug: Index out of bound
.smaller[
```C
int main()
{
  long a[10];
  for (long i = 0; i <= 10; i += 1) {
    a[i] = 1;
  }
}

```
]

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.tiny[
Version: 1.1

Last Updated: Mon Sep 14 11:12:21 +08 2020
]