Control Structures in Python

Control Structures

a. Conditional Statements

• Used for decision-making.

1. if Statements

i = 10

 # Checking if i is greater than 15

if (i > 15):

    print("10 is less than 15")

    

print("I am Not in if")

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2. if….else Statement

i = 20

 # Checking if i is greater than 0

if (i > 0):

    print("i is positive")

else:

    print("i is 0 or Negative")

  

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3. if…elif…else Statement

i = 25

 # Checking if i is equal to 10

if (i == 10):

    print("i is 10")

 # Checking if i is equal to 15

elif (i == 15):

    print("i is 15")

 # Checking if i is equal to 20

elif (i == 20):

    print("i is 20")

    

 # If none of the above conditions are true

else:

    print("i is not present")

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age = 10

if age > 18:
    print("Adult")
elif age == 18:
    print("Just turned adult")
else:

    print("Minor") 

b. Loops

• For Loop: Iterates over a sequence.

• Using range() with For Loop

With range(start, stop, step):

for i in range(1,10,3): #iterates from 1 to 9 , stepping by 2

    print(i)

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for i in range(5):

    print(i)

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for i in range(1,11):

    print(i*2)

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Iterating through a string

s = "Gods"

for i in s:

    print(i)

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fruits = ["apple","banana","cherry","Jackfruit"]

for fruit in fruits:

  print (fruit)

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for char in "python":

    print(char)

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• Break and Continue with For Loop

for i in range(5):

    if i == 3:

        break #exit the loop when i is 3

    elif i==1:

        continue #skips the iteration when i is 1

    print(i)

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Nested for loop

for i in range(3):

    for j in range(2):

    print(f"i={i},j={j}")

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Pass Statement with For Loop

# An empty loop

for i in 'geeksforgeeks':

    pass

print(i)

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Else Statement with For Loops

for i in range(1, 4):

    print(i)

else:  # Executed because no break in for

    print("No Break\n")

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Using Enumerate with for loop

In Python, enumerate() function is used with the for loop to iterate over an iterable while also keeping track of index of each item.

enumerate() function adds a counter to each item in a list or other iterable. It turns the iterable into something we can loop through, where each item comes with its number (starting from 0 by default). We can also turn it into a list of (number, item) pairs using list().

li = ["eat", "sleep", "repeat"]

for i, j in enumerate(li):

    print (i, j)

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•  While Loop: Repeats as long as a condition is true.

count = 0

while count < 5:

    print(count)

    count += 1

The break Statement with while loop
With the break statement we can stop the loop even 

if the while condition is true:

i = 1
while i < 6:
  print(i)
  if i == 3:
    break
  i += 1

The continue Statement with while loop
With the continue statement we can stop the current 

iteration, and continue with the next:

i = 0
while i < 6:
  i += 1
  if i == 3:
    continue
  print(i)

The else Statement

With the else statement we can run a block of code 
once when the condition no longer is true:

i = 1
while i < 6:
  print(i)
  i += 1
else:
  print("i is no longer less than 6")

while loop with pass statement

# An empty loop
a = 'geeksforgeeks'
i = 0

while i < len(a):
    i += 1
    pass
  
print('Value of i :', i)

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4. Functions

• Functions encapsulate reusable blocks of code.
• A function is a block of code which only runs when it is called.
• You can pass data, known as parameters, into a function.
• A function can return data as a result.

def greet(name):
    return f"Hello, {name}!"
print(greet("Alice"))

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def my_function(fname):
  print(fname + " Refsnes")

my_function("Emil")
my_function("Tobias")
my_function("Linus")

def my_function(fname, lname):
  print(fname + " " + lname)

my_function("Emil", "Refsnes")