Programming Constructs

Overview

In programming, sequence, iteration, and branching are the three fundamental constructs that form the basis of all algorithms. These constructs allow programmers to control the flow of a program, enabling it to make decisions, repeat tasks, and execute instructions in a specific order.

Understanding and effectively using these constructs is essential for developing efficient and correct programs.

Sequence

Definition:

• Sequence is the simplest construct, where instructions are executed one after another in the order they are written. Purpose:

• Ensures that tasks are completed in a specific order, which is critical for programs where the output of one step depends on the completion of the previous step.

INPUT name
PRINT "Hello, " + name
PRINT "Welcome to the program!"

name = input("Enter your name: ")
print("Hello, " + name)
print("Welcome to the program!")

Iteration

Iteration is the process of repeating a set of instructions until a certain condition is met.

Types of Iteration:

Condition-Based Iteration (While Loop):

Repeats as long as a condition is true.

WHILE count < 5
    PRINT count
    count = count + 1
ENDWHILE

count = 0
while count < 5:
    print(count)
    count += 1

Count-Controlled Iteration (For Loop):

Repeats a specific number of times.

FOR i = 1 TO 5
    PRINT i
ENDFOR

for i in range(1, 6):
    print(i)

Repeat-Until Loop (Post-Test Loop):

Executes the loop body at least once and repeats until a condition is met.

REPEAT
    INPUT value
UNTIL value > 0

Branching

Branching allows a program to make decisions and choose between different paths based on conditions.

Types of Branching:

IF Statement:

Executes a block of code if a condition is true.

IF score >= 50 THEN
    PRINT "You passed!"
ENDIF

if score >= 50:
    print("You passed!")

IF-ELSE Statement:

Provides an alternative action if the condition is false.

IF score >= 50 THEN
    PRINT "You passed!"
ELSE
    PRINT "You failed."
ENDIF

if score >= 50:
    print("You passed!")
else:
    print("You failed.")

IF-ELSEIF-ELSE Ladder:

Allows checking multiple conditions.

IF score >= 80 THEN
    PRINT "Grade A"
ELSEIF score >= 60 THEN
    PRINT "Grade B"
ELSE
    PRINT "Grade C"
ENDIF

if score >= 80:
    print("Grade A")
elif score >= 60:
    print("Grade B")
else:
    print("Grade C")

CASE/SWITCH Statement:

Simplifies multiple condition checks by matching a value to predefined cases.

CASE day OF
    "Monday": PRINT "Start of the workweek."
    "Friday": PRINT "Almost the weekend!"
    "Saturday", "Sunday": PRINT "It's the weekend!"
ENDCASE

Note: Python does not have a direct switch statement but can use if-elif or dictionaries for similar functionality.

Combining Constructs

In real-world programs, sequence, iteration, and branching are often combined to solve complex problems.

Example: Simple ATM System

Pseudocode:

START
BALANCE = 1000
WHILE TRUE
    PRINT "1. Check Balance"
    PRINT "2. Withdraw Money"
    PRINT "3. Exit"
    INPUT choice
    IF choice == 1 THEN
        PRINT "Balance: ", BALANCE
    ELSEIF choice == 2 THEN
        PRINT "Enter amount to withdraw:"
        INPUT amount
        IF amount <= BALANCE THEN
            BALANCE = BALANCE - amount
            PRINT "Withdrawal successful."
        ELSE
            PRINT "Insufficient funds."
        ENDIF
    ELSEIF choice == 3 THEN
        PRINT "Goodbye!"
        BREAK
    ELSE
        PRINT "Invalid choice."
    ENDIF
ENDWHILE

Benefits of Using Constructs

1. Sequence: Ensures tasks are completed in the correct order.
2. Iteration: Automates repetitive tasks, reducing redundancy.
3. Branching: Enables dynamic decision-making, allowing the program to handle different inputs and scenarios.

Note Summary