readme.md

Conditional Statements

The conditional statements are a very fundamental part of any program as it helps to change the flow of control (which is generally top to bottom) depending on a given condition.

Let us consider an example where we print whether a given number is Odd or Even.

Code snippet:

if number % 2 == 0:
	print ("Number is even")
else:
	print ("Number is odd")

Now, if the entered number is 5, the if statement will check if the remainder of 5 divided by 2 is 0 or not. As it is not 0, it skips the lines of code within the if statement and the flow of control is shifted to the else part and the lines of code written under it is executed.

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There are two types of conditional statements:

1. if - else if - else

Here is a code that prints the grade based on the marks.

• In C++:

if (marks >= 90)    {
    cout << "A";
}
else if (marks >= 80)    {
    cout << "B";
}
else if (marks >= 70)    {
    cout << "C";
}
else if (marks >= 40)    {
    cout << "D";
}
else {
    cout << "F";
} 

In Python, else if is written as elif.

• In Python:

if marks >= 90:
   print ("A")
elif marks >= 80:
   print ("B")
elif marks >= 70:
   print ("C")
elif marks >= 40:
   print ("D")
else:
   print ("F")

2. switch case statements

In switch case, we take a value from user which is generally integer or of a character data type based on which the corresponding case is executed.

It is used in-place of if statement if the decision making branches are independent of each other.

Let us assume that a player is picking a colour for playing Ludo, and based on what he enters, i.e., R, B, Y and G, he is given Red, Blue, Yellow and Green respectively. In case, they enter any other alpahabet, the code returns an error message as no colour is associated with that alphabet.

• A code in C++ to implement the same:

switch (alphabet) {
        case 'R':
            cout << "Red";
            break;
        case 'B':
            cout << "Blue";
            break;
        case 'Y':
            cout << "Yellow";
            break;
        case 'G':
            cout << "Green";
            break;
        default:
            cout << "No other colour exists";
    }

• Note: Python does not have switch case statements.

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Loops

Loops are used to execute a block of code as many times we want without writing the same code over and over again. The flow of control breaks out from the loop when the provided condition is false or a break statement is used.

Let us take an example where we print all the even numbers upto 10.

There are two types of loop statements:

1. for statement

Let us take an example where we print all the even numbers upto 10.

• In C++:

for (int i = 2; i <= 10; i+=2) {
  cout << i << "\n";
}

int i = 2 initializes the value of i to 2

and i += 2 keeps on incrementing the value of i by 2

until i <= 10 becomes false

* In Python: ```python for i in range(2, 11, 2): print (i) ```

*Output: 2 4 6 8 10

The range function takes in three parameters - the first paramter is the starting value, the second parameter is the ending value + 1, and the third paramter is the increment value.

Here, range(2, 11, 2) tells the program that it should run the loop for all the values of i between 2 to (11-1) and keep incrementing the value of i by 2.

2. while / do while statements

A while statement always checks if the condition provided is True or False at the beginning of the loop and in case it is True, the block of code within the loop is executed. Otherwise, the loop is terminated. As it always checks the condition at the beginning it is also called as Entry-Controlled loop.

• A code in C++ to implement the same:

int i = 2;
while (i <= 10)	{
	cout << i << "\n";
	i += 2;
}

• In Python:

i = 2
while i <= 10:
   print (i)
   i += 2

In the above codes, the while loop runs until the value of i is 10.

In a do while loop, the validity of the condition is checked at the end of loop. Hence, the code runs atleast once even if the provided condition is False. Also known as Exit-Controlled loop as condition is checked after the loop body is executed.

If I modify the above code to a do while loop, it will print even numbers upto 12 as it checks the condition after the loop is executed.

Code snippet for do-while:

int i = 2;
do	{
	cout << i << "\n";
	i += 2;
}while (i <= 10);

Output: 2 4 6 8 10 12

• Note: In Python, we do not have do-while loops.

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Functions

In programming, we often have a block of code which performs a specific task and many times within the program, we may need to use the exact same piece of code. In this case, to eliminate repeatedly writing the same code over and over again and also to maintain readability of the code, we define functions for the same.

• A function can be reused multiple times.
• You can send data to a function which it uses to perform a task.
• A function generally returns a value to the main function which is then used to perform other operations.
• Every programming language has some built-in functions which you can use.
• You can also write functions on your own.
• When you call a function, the flow of control shifts from the main function to the function which is always executed from top to bottom.
• A function can call another function or even call itself (known as recursive functions).
• A return function takes the flow of control out of the function and goes back to the main function.

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Let us consider a situation where I want to print all the prime numbers between 1 to 100:

So, we can write a function to check if a number is prime or not. It returns a boolean data type value based on which we decide whether the number should be printed or not.

Code Snippet for the isPrime function:

def isPrime (number: int) -> bool:
	factors = 0
	for i in range (2, (number // 2) + 1):
		if number % i == 0:
			factors += 1
	if factors == 0:
		return True
	return False

The topmost line of a function is called a function header.

In, def isPrime (number: int) -> bool: , the parameters within the bracket tells the program how many parameters this function will accept and what are they called.

In this case, the function header tells the program that it has to pass one parameter to the isPrime function and that parameter/ variable will be refered to as number inside the function.

Now let us use this function to print prime numbers upto 100:

for i in range(1, 101):
	if isPrime(i):
		print (i)

• This code uses the isPrime function to determine if the number is prime or not for every value of i from 1 to 100 and prints the prime numbers only.
• This not only just increases the readability of the main program but the isPrime function can be used by other programs too.

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