Introduction

In programming, two fundamental concepts help us control how a program behaves: decision-making and repetition. Decision-making allows a program to choose different paths based on conditions, while repetition lets a program execute a block of code multiple times without rewriting it. These concepts are implemented using conditionals and loops, respectively.

Imagine you are following a recipe. Sometimes, you decide to add salt only if the dish tastes bland (a decision). Other times, you stir the mixture repeatedly until it thickens (a repetition). Similarly, in programming, conditionals help the computer make choices, and loops help it repeat tasks efficiently.

Mastering loops and conditionals is essential for writing efficient programs and solving complex problems, especially in competitive exams where time and accuracy matter.

Conditionals

Conditionals are statements that perform different actions based on whether a condition is true or false. The condition is a logical expression that evaluates to a boolean value: true or false.

The simplest conditional is the if statement. It executes a block of code only if the condition is true.

If Statement Syntax

if (condition) {    // code to execute if condition is true}

For example, in Python:

if temperature > 30:    print("It's a hot day")

This code prints "It's a hot day" only if the temperature is greater than 30.

If-Else Statement

Sometimes, you want to choose between two paths: one if the condition is true, and another if it is false. This is done using an if-else statement.

if (condition) {    // code if true} else {    // code if false}

Example in Python:

if temperature > 30:    print("It's a hot day")else:    print("It's not a hot day")

Nested Conditionals

You can place one conditional inside another to check multiple conditions step-by-step. This is called nested if statements.

if (condition1) {    if (condition2) {        // code if both conditions are true    } else {        // code if condition1 true but condition2 false    }} else {    // code if condition1 false}

Example:

if age >= 18:    if has_voter_id:        print("Eligible to vote")    else:        print("Need voter ID to vote")else:    print("Not eligible to vote")

How Conditionals Control Flow

Conditionals direct the flow of program execution by choosing which blocks of code run. This decision-making is essential for programs that react differently based on input or state.

graph TD    Start --> Condition{Is condition true?}    Condition -- Yes --> TrueBlock[Execute True Block]    Condition -- No --> FalseBlock[Execute False Block]    TrueBlock --> End[End]    FalseBlock --> End

Loops

Loops allow a program to repeat a block of code multiple times. This is useful when you want to perform the same operation on many items or until a certain condition is met.

For Loop

A for loop repeats a block of code a known number of times. It usually involves three parts:

• Initialization: Set the starting point.
• Condition: Check if the loop should continue.
• Update: Change the loop variable to eventually end the loop.

Example in C:

for (int i = 1; i <= 5; i++) {    printf("%d\n", i);}

This prints numbers 1 to 5.

While Loop

A while loop repeats as long as a condition remains true. It is useful when the number of iterations is not known beforehand.

while (condition) {    // code to repeat}

Example in Python:

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

Nested Loops

You can place one loop inside another to handle multi-dimensional data or repeated tasks within repeated tasks.

Example: Printing a multiplication table up to 3x3:

for i in range(1, 4):    for j in range(1, 4):        print(i * j, end=' ')    print()

Loop Execution Flow

graph TD    Start --> Initialization    Initialization --> ConditionCheck{Is condition true?}    ConditionCheck -- Yes --> ExecuteBlock[Execute loop block]    ExecuteBlock --> Update    Update --> ConditionCheck    ConditionCheck -- No --> End

Loop Control Statements

Sometimes, you want to change the normal flow of loops. Two important statements help with this:

Break Statement

The break statement immediately exits the loop, skipping the remaining iterations.

for i in range(1, 10):    if i == 5:        break    print(i)

This prints numbers 1 to 4 and stops when i becomes 5.

Continue Statement

The continue statement skips the current iteration and moves to the next one.

for i in range(1, 6):    if i == 3:        continue    print(i)

This prints 1, 2, 4, 5 (skips 3).

Formula Bank

Worked Examples

N = 10sum = 0for i in range(1, N+1):    sum += iprint("Sum =", sum)    

num = 29is_prime = Trueif num <= 1:    is_prime = Falseelse:    for i in range(2, int(num**0.5) + 1):        if num % i == 0:            is_prime = False            breakif is_prime:    print(num, "is prime")else:    print(num, "is not prime")    

for i in range(1, 11):    for j in range(1, 11):        print(i * j, end='\t')    print()    

arr = [12, 45, 7, 89, 34]max_val = arr[0]for num in arr[1:]:    if num > max_val:        max_val = numprint("Largest element is", max_val)    

numbers = [3, 7, 5, 8, 10]for num in numbers:    if num % 2 == 0:        print("First even number is", num)        break