Functions (and recursion)

Functions in math

f(x)=x*x
y(x)=x*x
y=x*x
y(10)=100
----OR-----
f(x)=x*x
f(x){
    return x*x
}
outputType f(inputType x){
    return x*x
}
                    

Function with args

Function square

Functions in programming

#include <iostream> 

void hello() // function
{   // { 
    // ... function body 
    // } 
    std::cout << "hello world" << std::endl;
}

int main(){
    hello(); // the calling of the function hello()

    return 0;
}
   
                        

Functions in programming - Python

import ...
def hello():  # function
    # {
    # ... function body
    # }
    print("hello world")
def main():
    hello()
if __name__ == "__main__":
    main()
                        

Function in C++

Function in Python

Main() function...

#include <iostream> 

int main(){ // function main() // output type is int
    std::cout << "hello world" << std::endl;

    return 0; // returns int 0 value
}
                        

Add player function

#include <iostream> 

int main(){

    std::cout << "The game for 4 players:" << endl;
    std::cout << "Enter the names of you friends:" << endl;
    // Data block
    char player1[100];
    // Input block
    std::cout << "Player 1: "; 
    std::cin >> player1;
    
    // Data block
    char player2[100];
    // Input block
    std::cout << "Player 2: "; 
    std::cin >> player2;

    // Data block
    char player3[100];
    // Input block
    std::cout << "Player 3: "; 
    std::cin >> player3;

    // Data block
    char player4[100];
    // Input block
    std::cout << "Player 4: "; 
    std::cin >> player4;

    return 0;
}
                        

#include <iostream> 

int main(){
    int array1[5] = {1,2,3,4,5}; // Array 1

    for(int i = 0; i < 5; i++){
        std::cout << "Array1[" << i+1 << "]: " << array1[i] << "\n";
    }

    int array2[7] = {1, 2, 3, 4, 5, 6, 7}; // Array 2

    for(int i = 0; i < 5; i++){
        std::cout << "Array2[" << i+1 << "]: " << array1[i] << "\n";
    }

    int array3[10] = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; // Array 3

    for(int i = 0; i < 5; i++){
        std::cout << "Array3[" << i+1 << "]: " << array1[i] << "\n";
    }

    return 0;
}
                        

DRY - Don't repeat yourself

Lambda functions, Recursion and Generators

Lambda functions

Lambda functions

Lambda functions: Ternary operation

Lambda functions: Ternary operation

#include <iostream> 

int main(){
    condition = true;
    int number = condition ? 42 : 13
}
                        

condition = True
number = 42 if condition else 13
print(number)
                        

Ternary operation

Lambda functions

Lambda functions

Lambda functions

Lambda functions: Fish Tanks Volume Ex

# Fish Tanks Volume 
def calculateFishTanks():
    # Only here we use function 5 times, so make it lambda
    pass


volume = lambda x, y, z, type="cm^3": "Volume: " + str(x * y * z) + " " + type

print(volume(10, 15, 20))
                        

Lambda functions == Anonymous functions

Lambda functions: usage

Lambda functions: filter example

data = ["rabbit", "chuck", "Joe", "duck", "rock", "joke", "docker", "hope"]
listfilter = list(filter(lambda x: ('k' in x), data))

# Prints ['chuck', 'duck', 'rock', 'joke', 'docker']
print(listfilter)
                        

Recursion

Quiz: Where the recursion here?

Quiz: Where the recursion here?

Quiz: Where the recursion here?

Quiz: Where the recursion here?

Quiz: Where the recursion here?

Quiz: Where the recursion here?

Christopher Nolan - Inception (2010)

Portal the game

Generators

Quiz: What is generated here?

Quiz: What is generated here?

Quiz: What is generated here?

Quiz: What is generated here?

What you can say about generators?

Generators vs Iterators

Generators vs Iterators

Generators vs Iterators

Why we cannot use [index]

Why we cannot use [index]

int* a = new int[10]{1,2,3,4,5,6,7,8,9,10};
a+sizeof(int)*index
                        

It is like in FOR

Generators vs Iterators

# list comprehension
doublesGen = (2 * n for n in range(50))

# same as the list comprehension above
doublesList = list(2 * n for n in range(50)) # 0 - 49
                        

Generators

Generators

Generators Task

Generators Task

Generators Task Gauss

Generators Task Gauss

def first_n(n):
    '''Build and return a list'''
    num, nums = 0, []
    while num <= n:
        nums.append(num)
        num += 1
    return nums


sum_of_first_n = sum(first_n(100))
print(sum_of_first_n)
                        

Generators Task Gauss

num, nums = 0, []
nums.append(num)
                        

Generators Task Gauss

yield
                        

Generators Task Gauss

Generators: yield

def simpleGeneratorFun(): 
    yield 1            
    yield 2            
    yield 3  
                        

Generators: yield

# Python Generator Function with Multiple Yield

def testGen():
    x = 1
    print('First yield')
    # Generator function has many yield statements
    yield x

    x *= 2
    print('Second yield')
    yield x

    x *= 3
    print('Last yield')
    yield x

# Call the generator
iter = testGen()

# Invoke the first yield
next(iter)

# Invoke the second yield
next(iter)

# Invoke the last yield
next(iter)
                        

Generators Task Gauss

# a generator that yields items instead of returning a list
def firstn(n):
    num = 0
    while num <= n:
        yield num
        num += 1
                        

Generators: yield

Generators: yield

def csv_reader(file_name):
    for row in open(file_name, "r"):
        yield row
                        

Generators: yield

def infinite_sequence():
    num = 0
    while True:
        yield num
        num += 1
                        

Generators: yield

Generators in Math

Generators