JavaScript Control Flow MCQs

1. Conditional Statements

These are used to perform different actions based on different conditions.

if Statement

let age = 18;

if (age >= 18) {
  console.log("You are eligible to vote.");
}

if...else Statement

let score = 45;

if (score >= 50) {
  console.log("You passed!");
} else {
  console.log("You failed.");
}

if...else if...else Statement

let marks = 75;

if (marks >= 90) {
  console.log("Grade: A");
} else if (marks >= 75) {
  console.log("Grade: B");
} else if (marks >= 50) {
  console.log("Grade: C");
} else {
  console.log("Fail");
}

switch Statement

Used when you have many conditions to check based on a single variable.

let day = "Monday";

switch (day) {
  case "Monday":
    console.log("Start of the week");
    break;
  case "Friday":
    console.log("End of the week");
    break;
  default:
    console.log("Regular day");
}

---

2. Loops

Loops execute a block of code a number of times until a specified condition is false.

for Loop

for (let i = 1; i <= 5; i++) {
  console.log("Count: " + i);
}

while Loop

let i = 1;

while (i <= 5) {
  console.log("Count: " + i);
  i++;
}

do...while Loop

This loop runs at least once even if the condition is false at the beginning.

let i = 1;

do {
  console.log("Count: " + i);
  i++;
} while (i <= 5);

for...of Loop

Used to iterate over iterable objects like arrays.

let fruits = ["apple", "banana", "cherry"];

for (let fruit of fruits) {
  console.log(fruit);
}

for...in Loop

Used to iterate over the enumerable properties of an object.

let student = { name: "Alice", age: 20, grade: "A" };

for (let key in student) {
  console.log(key + ": " + student[key]);
}

---

3. Control Flow Statements

break Statement

Exits the current loop or switch statement.

for (let i = 1; i <= 10; i++) {
  if (i === 5) break;
  console.log(i);
}

continue Statement

Skips the current iteration and continues with the next one.

for (let i = 1; i <= 5; i++) {
  if (i === 3) continue;
  console.log(i);
}

return Statement

Used to exit a function and return a value.

function add(a, b) {
  return a + b;
}
console.log(add(5, 3)); // 8

---

Best Practices

• Always use break in switch to prevent fall-through.
• Use const or let instead of var in loops.
• Avoid deeply nested if statements when possible; use functions or early returns.

Control Flow MCQs

1. What is the primary purpose of an if-else statement in JavaScript?

2. What will be the output of the following code?

    let x = 10;
    if (x > 5) {
        console.log('True condition');
    } else {
        console.log('False condition');
    }
    

3. What does a switch statement evaluate?

4. What will be the output of the following code?

    let choice = 'B';
    switch (choice) {
        case 'A':
            console.log('You chose A');
            break;
        case 'B':
            console.log('You chose B');
            break;
        default:
            console.log('Invalid choice');
    }
    

5. What is the ternary operator primarily used for?

6. What will be the output of the following code?

    let age = 16;
    if (age >= 18) {
        console.log('Allowed');
    } else {
        console.log('Not allowed');
    }
    

7. What is the purpose of the 'break' statement in a switch case?

8. What will be the output of the following code?

    let age = 18;
    let status = age >= 18 ? 'Adult' : 'Minor';
    console.log(status);
    

9. What is the purpose of an else-if statement?

10. What will be the output of the following code?

    let number = 2;
    switch (number) {
        case 1:
            console.log('One');
            break;
        case 2:
            console.log('Two');
            break;
        case 3:
            console.log('Three');
            break;
        default:
            console.log('Not a number');
    }
    

11. How does the if-else statement work in JavaScript?

12. What will be the output of the following code?

    let a = 5;
    let b = 10;
    if (a < b) {
        console.log('A is less than B');
    } else {
        console.log('A is greater than or equal to B');
    }
    

13. When is it preferable to use a switch statement over if-else statements?

14. What will be the output of the following code?

    let isLoggedIn = true;
    if (isLoggedIn) {
        console.log('Access granted');
    } else {
        console.log('Access denied');
    }
    

15. What happens if no case in a switch statement matches the input?

16. What will be the output of the following code?

    let age = 15;
    let status = (age < 18) ? 'Minor' : 'Adult';
    console.log(status);
    

18. What is a common use of the ternary operator?

18. What will be the output of the following code?

    let fruit = 'Banana';
    switch (fruit) {
        case 'Apple':
            console.log('Apple is red');
            break;
        case 'Banana':
            console.log('Banana is yellow');
            break;
        default:
            console.log('Unknown fruit');
    }
    

19. What type of expression can be used as a condition in an if statement?

20. What will be the output of the following code?

    let num = 0;
    if (num > 0) {
        console.log('Number is positive');
    } else if (num < 0) {
        console.log('Number is negative');
    } else {
        console.log('Number is zero');
    }