Languages & Functions

# Languages & Functions

Week 7

---

## Review

![](https://media1.giphy.com/media/v1.Y2lkPTc5MGI3NjExcXFhOTFjMWQwNzVudWZkNmoxaDVvZmhtMmtna2NvOG83eWN6aWNxNyZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/eGxkm7b2hzDfkNvjo7/giphy.gif)

What does CPU stand for?

Central Processing Unit

What does a CPU do?

Lots of math (computer brain)

What are the three _logical operators_ in Python?

(aka boolean operators)

`and`, `or`, `not`

What is the output?

```py
print(not True)
```

```
False
```

What is the output?

```py
print(True and True or False)
```

```
True
```

---

## Programming Languages

What is a language?

System of words to communicate

Levels of Abstraction

- Machine code 
- Assembly language 
- Low-level 
- High-level

NOTES:
- Binary
- x86, ARM, MIPS
- C, Rust
- Python, JavaScript, C#, Swift

Machine Code (binary)

```
0110 1000 0010 0001 0000 1010 0000 0000
1010 0011 0000 1101 0000 0000 0000 0110
0110 1000 0110 1111 0111 0010 0110 1100 0110 0100
1010 0011 0000 1000 0000 0000 0000 0110
0110 1000 0110 1111 0010 1100 0010 1000 0101 0111
1010 0011 0000 0100 0000 0000 0000 0110
0110 1000 0100 1000 0110 0101 0110 1100 0110 1100
1010 0011 0000 0000 0000 0000 0000 0110
1011 0000 0000 0000 0000 0000 0000 0110
1011 0000 0000 0000 0000 0000 0000 0000
1011 0000 0000 0000 0000 0000 0000 0001
0110 1000 0000 0100 0000 0000 0000 0000
1100 1101 1000 0000
0110 1000 0000 0001 0000 0000 0000 0000
1100 1101 1000 0000
```

Assembly (RISC)

```asm
.data
hello:
    .asciiz "Hello, World!\n"

.text
main:
    li a0, 4
    la a0, hello
    li a7, 4
    ecall
    li a7, 10
    ecall
```

Low-Level Language (C)

```c
int main() {
  printf("Hello, World!\n");
  return 0;
}
```

High-Level Language (Python)

```py
print("Hello, World!")
```

---

## Common Languages

C++

```cpp
#include <iostream>
#include <string>

int main() {
    std::string user_input;
    std::cout << "Enter something: ";
    std::getline(std::cin, user_input);
    std::cout << user_input << std::endl;
    return 0;
}
```

Java

```java
import java.util.Scanner;

public class Echo {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        System.out.print("Enter something: ");
        String userInput = scanner.nextLine();
        System.out.println(userInput);
    }
}
```

JavaScript

```js
const readline = require('readline').createInterface({
  input: process.stdin,
  output: process.stdout
});

readline.question('Enter something: ', (userInput) => {
  console.log(userInput);
  readline.close();
});
```

Python

```py
user_input = input("Enter something: ")
print(user_input)
```

---

## Semantics vs. Syntax

What are "semantics?"

The meaning we convey with language

What is "syntax?"

Words, character, grammar

Comments are for _semantics_

```py []
# TODO Tell the user "hello"
```

More than one valid syntax

```py [2|3|4]
# Tell the user "hello"
print("Hello")
print( f'Hello' )
print('H' + 'e' + 'l' + 'l' + 'o')
```

(some are better than others)

Syntactic sugar

```py [|3-4|6-7]
if levi_has_fingers:
  print("High five!")
else:
  print("RIP Levi's digits")

if not levi_has_fingers:
  print("RIP Levi's digits")
```

---

## Functions

What is a function?

A reusable section of code

Define + call

```py [1-3|5-6]
# Function definition
def print_foo():
  print("foo")

# Function call
print_foo()
```

Definition

```py [3-5]
message = ""

def laugh_contagiously():
  message += "ha"
  print(message)

laugh_contagiously()
laugh_contagiously()
laugh_contagiously()
```

Call

```py [7-9]
message = ""

def laugh_contagiously():
  message += "ha"
  print(message)

laugh_contagiously()
laugh_contagiously()
laugh_contagiously()
```

---

## Parameters

f(x) = -x

f(x) = -x

|  x   |   y   |
|-----|--------|
| 5   | <span class="fragment green">-5</span>   |
| 0   | <span class="fragment green">0</span>    |
| -10 | <span class="fragment green">10</span>   |

f(x) = -x

```py []
def f(x):
  print(x * -1)
```

```py []
def say_hello(name):
  print(f"Hello, {name}!")

say_hello("Tim")
say_hello("Skyler")
say_hello("Nolan")
say_hello("Levi")
```

```py []
def print_sum(x, y):
  print(x + y)

print_sum(4, 6)
print_sum(-1000, 1)
```

```txt
10
-999
```

---

## Return

f(x) = -x

```py [|2|4|5]
def f(x):
  return x * -1

y = f(5)
print("f(5) is", y)
```

What does this output?

```py []
def compute_sum(x, y):
  return x + y

compute_sum(4, 6)
compute_sum(-1000, 1)
```

Nothing!

```py []
def compute_sum(x, y):
  return x + y

print( compute_sum(4, 6) )
print( compute_sum(-1000, 1) )
```

```txt
10
-999
```

What does this output?

```py []
def say_hi(name):
  print( "Hi", name )

def append_hi(name):
  return "Hi " + name

print( say_hi("Steve") )
print( append_hi("Steve") )
```

```txt
Hi Steve
None
Hi Steve
```

---

## Exercise

Implement functions so this ad-lib program works!

```py
noun1 = get_word("noun")
noun2 = get_word("noun")
verb = get_word("verb")
print_story(noun1, noun2, verb)
```

---

![Jimmy Fallon thats it](https://media4.giphy.com/media/v1.Y2lkPTc5MGI3NjExd2NmamM3NmR2c3RtenR3bGV5dnR1MnNyM3BzNnh3ZGNwYTFyZ2V6YyZlcD12MV9pbnRlcm5hbF9naWZfYnlfaWQmY3Q9Zw/uSZQ6WPIcpouUEpNTe/giphy.gif)