Control Structure.md

Decision Making: [Condition Statement/ Control Structures]

Decision making in the anticipation of conditions occuring during the execution of a program and specified action taken according to the conditions. Python programming language provides the following Decision Control Statements are:

• 1. if
• 2. if-else
• 3. if-elif-else
• 4. nested if

if statement:

The if statement contains a logical expression using which the data is compared and a decision is made based on the result of the comparision.

Syntax:

  if(expression):
    statement(s)
  # Note: In python statements in a block are uniformly indented after : symbol.

Flow Diagram:

  # Example:
  a = int(input("Enter a value: "))
  b = int(input("Enter b value: "))
  if(a>b):
    print("Inside of if-block")
    print(f"Largest element is: {a}")
  print("Outside of if-block")

  ''' output: 
  Enter a value: 5
  Enter b value: 2
  Inside of if-block
  Largest element is: 5
  Outside of if-block
  '''

if-else statement:

An else statement can be combined with an if-statement. An else statement contains a block of code that executes if the conditional expression in the if-statement resolves to 0 or a False value.

Syntax:

  if(expression):
    statement(s)
  else:
    statement(s)

Flow Diagram:

  # Example:
  a = int(input("Enter a value: "))
  b = int(input("Enter b value: "))
  if(a > b):
    print("Inside of if-block")
    print(f"Largest element is: {a}")
  else: 
    print("Inside of else-block")
    print(f"Largest element is: {b}")
  print("Outside of if-else-block")

  ''' Output:
    Enter a value: 5
    Enter b value: 2
    Inside of if-block
    Largest element is: 5
    Outside of if-else-block
    
    Enter a value: 2
    Enter b value: 4
    Inside of else-block 
    Largest element is: 4
    Outside of if-else-block
  '''

if-elif-else-statement:

The elif statement allows you to check multiple expressions for True and execute a block of code as soon as one of the condition evaluates to True.

Syntax:

if(expression1):
  statement(s)
elif (expression2):
  statement(s)
elif (expression3):
  statement(s)
else:
  statement(s)

Flow Diagram:

# Example:
hours = int(input("Enter time in hours: "))
if(hours>=6 and hours<12):
  print("Good Morning :)")
elif (hours>=12 and hours<16):
  print("Good Afternoon :)")
elif (hours>=16 and hours<19):
  print("Good Evening :)")
else:
  print("Good Night :>")
  
''' Output:
Enter time in hours: 15
Good Afternoon :)
'''

nested-if statement:

Nested if statements are an if statement inside another if statement.

Syntax:

  if(expression):
    if(expression):
      statement(s)
  else:
    statement(s)

Flow Diagram:

  # Example:
  a = 5
  b = 10
  c = 15
  if a > b:
    if a > c:
        print("a value is big")
    else:
        print("c value is big")
  elif b > c:
      print("b value is big")
  else:
      print("c is big")
  
  # output: c is big

Single Statement Suites:

If the suits if an if clause consists only of a single line, it may go on the same line as the header statement.

  # Example:
  num1 = int(input("Enter first number 1: "))
  num2 = int(input("Enter second number 2: "))

  if(num1 > num2): print(f'{num1} is greatest number')
  else: print(f"{num2} is greatest number")

  ''' Output:
  Enter first number 1: 5
  Enter second number 2: 2
  5 is greatest number
  '''