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Python and The Basics of Programming.
Loops (while, do-while, for)


Lesson 3

Author: Egoshkin Danila Igorevich

What are the Loops?

Loops

We will ride the slide until we get bored.
When we do some action(s) while(until) some condition is true (we do not get bored)

Loops

There are three types of loops:
while, do-while, for, foreach


An some special:
recursion

Loops: while


while(condition == true)
{
    // Do some actions here if "condition == true"
    // It will repeat actions if "condition == true"
}

Loops: while

Loops: while

Examples: Gotta Blast, Parrot

Loops: while

Example: Gotta Blast 

int main() 
{
    int i = 3;
    while (i > 0) { // 3 2 1
        cout << i << endl; 
        i--; // i = i - 1;
    }
    cout << "Gotta Blast!" << endl;
}

Loops: while

Example: Parrot 

int main() {
    char str[100] = "";
    cout << "Here is a Parrot, say something: ";
    cin.getline(str, 100);
    // strcmp = 0 - performs a case-sensitive comparison of two strings.
    // stricmp = 0 - performs a non-case-sensitive comparison of two strings.
    while (_stricmp(str, "bye") != 0 && 
           _stricmp(str, "goodbye") != 0) {
        cout << "- Parrot: " << str << endl;
        cout << "- You: ";
        cin.getline(str, 100);
    }
    cout << "- Parrot: Bye Bye, Goodbye!";
}

Loops: Nested loops - Nested while

A nested loop means a loop statement inside another loop statement. That is why nested loops are also called “loop inside loops“.
Like with If..Else inside If..Else 

while(condition1 == true) // 1D
{
    while(condition2 == true) // 2D
    {
        while(condition3 == true) // 3D
        {
            ... // ToDo
        }
    }
}

Loops: do-while



do
{
    // Do some actions here.
    // It will make action first 
    // and only then will think repeat it 
    // in "while" if "condition == true" 
    // or not
}
while(condition == true)

Loops: do-while

Loops: while vs do-while

Loops: do-while in Python???

Is there a do-while loop in Python?

Loops: break and continue (and Python`s Pass)

Break and continue

The break and continue statements in Python are used to skip parts of the current loop or break out of the loop completely.

Break

Continue

Pass

The pass statement can be used to fill in code initially that could be used in the future. It may sound silly to use the pass statement in parts of the code that would be deleted anyway later, but it proves to be very useful in the initial stages of development for faster development.
ToDo

while and if

while and else


                        while counter < 3:
                            pass
                        else:
                            pass

Loops: for vs while

What is the difference?
WHILE 

int i = 0;
while(i < 10)
{
    std::cout << i << " ";
    i++; // i = i + 1;
}
FOR 

for(int i = 0; i < 10; i++) {
    std::cout << i << " ";
}

Loops: for in Python

For style by range
FOR C++ 

for(int i = 0; i < 10; i++) {
    std::cout << i << " ";
}
FOR Python 

for x in range(10):
  print(x)

Loops: for in Python

For with start point
FOR C++ 

for(int i = 5; i < 10; i++) {
    std::cout << i << " ";
}
FOR Python 

for x in range(5, 10):
  print(x)

Loops: for in Python

For with user step
FOR C++ 

for(int i = 0; i < 10; i+=3) {
    std::cout << i << " ";
}
FOR Python 

for x in range(0, 10, 3):
  print(x)

Are there new ideas?

(About the difference between for and while)

Loops: for in Python

FOR C++ 

for (int i = 1; i <= 10; i++) {
    std::cout << i << " ";
    i = i * 2;
}
FOR Python 

???
This is not a real example
It is artificial example

Loops: for in Python

FOR C++ 

for(int i = 1; i <= 10; i++) {
    if(i % 2 == 1)
        i+=3;
    if(names[i] == "John")
        i+=3;
}
FOR Python 

???
It is imposible with for in python, only with while...
But...

Loops: for == foreach in Python

foreach thought for 

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

  for (int i : myint)
  {
    std::cout << i << '\n';
  }
}
foreach thought std 

#include <iostream>
#include <algorithm> // contains std::for_each
#include <vector>

int main()
{
  std::vector<int> v {1, 2, 3, 4, 5};

  std::for_each(v.begin(), v.end(), [](int i)
  {
    std::cout << i << '\n';
  });

  std::cout << "reversed but skip 2 elements:\n";

  std::for_each(v.rbegin()+2, v.rend(), [](int i)
  {
    std::cout << i << '\n';
  });
}
FOR 

for character in "Python":
  print(character)


programming_languages = ["Python", "JavaScript", "Java", "C++"]

# ітерація над кожним елементом всередині списку
for language in programming_languages:
  print(language)
Break, Pass, Continue, Enumerate

Links:

Thanks for your attention :)