Chapter 7 Beginner 62 Questions

Practice Questions — Loops (for, while, do-while) and Patterns

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9 Easy

12 Medium

13 Hard

Topic-Specific Questions

Question 1

Easy

What is the output?

for (int i = 1; i <= 5; i++) {
    cout << i << " ";
}

i goes from 1 to 5 inclusive.

1 2 3 4 5

Question 2

Easy

What is the output?

for (int i = 5; i >= 1; i--) {
    cout << i << " ";
}

Counting downward from 5 to 1.

5 4 3 2 1

Question 3

Easy

What is the output?

int x = 1;
while (x <= 3) {
    cout << "Hello" << endl;
    x++;
}

x starts at 1 and increments to 4.

Hello
Hello
Hello

Question 4

Easy

What is the output?

int n = 10;
do {
    cout << n << " ";
    n++;
} while (n < 5);

do-while executes the body at least once.

10

Question 5

Easy

What is the output?

for (int i = 0; i < 5; i++) {
    cout << i << " ";
}

Starts at 0, goes up to but not including 5.

0 1 2 3 4

Question 6

Medium

What is the output?

for (int i = 1; i <= 4; i++) {
    if (i == 3) continue;
    cout << i << " ";
}

continue skips the rest of the current iteration.

1 2 4

Question 7

Medium

What is the output?

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 2; j++) {
        cout << i << j << " ";
    }
}

Inner loop runs completely for each outer iteration.

11 12 21 22 31 32

Question 8

Medium

How many times does "Hello" print?

for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 4; j++) {
        cout << "Hello" << endl;
    }
}

Outer: 3 iterations. Inner: 4 iterations each.

12 times

Question 9

Medium

What is the output?

int sum = 0;
for (int i = 1; i <= 10; i++) {
    if (i % 2 == 0) sum += i;
}
cout << sum;

Sum of even numbers from 1 to 10.

30

Question 10

Medium

What is the output?

int i = 5;
while (i > 0) {
    cout << i << " ";
    i -= 2;
}

i decreases by 2 each time: 5, 3, 1, -1.

5 3 1

Question 11

Medium

What is the output?

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= i; j++) {
        cout << "* ";
    }
    cout << endl;
}

Row i has i stars.

*
* *
* * *

Question 12

Hard

What is the output?

for (int i = 0; i < 5; i++) {
    if (i == 3) break;
    cout << i << " ";
}

break exits the loop entirely when i equals 3.

0 1 2

Question 13

Hard

What is the output?

int x = 1;
for (int i = 1; i <= 4; i++) {
    x *= i;
}
cout << x;

This computes 1 * 1 * 2 * 3 * 4.

24

Question 14

Hard

What is the output?

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        if (i == j) continue;
        cout << i << j << " ";
    }
}

continue in the inner loop skips pairs where i equals j.

12 13 21 23 31 32

Question 15

Hard

What is the output?

for (int i = 100; i >= 1; i /= 3) {
    cout << i << " ";
}

Integer division: 100/3=33, 33/3=11, 11/3=3, 3/3=1, 1/3=0.

100 33 11 3 1

Question 16

Hard

What is the output?

int num = 1;
for (int i = 1; i <= 4; i++) {
    for (int j = 1; j <= i; j++) {
        cout << num++ << " ";
    }
    cout << endl;
}

This is Floyd's Triangle. num increments continuously.

1
2 3
4 5 6
7 8 9 10

Question 17

Easy

What is the difference between a while loop and a do-while loop?

Think about when the condition is checked.

A while loop checks the condition before each iteration; if false initially, the body never executes. A do-while loop checks the condition after each iteration, so the body always executes at least once.

Question 18

Medium

In a range-based for loop, what is the difference between for (auto x : arr) and for (auto& x : arr)?

Think about copies vs references.

auto x creates a copy of each element. Modifying x does not change the array. auto& x creates a reference to each element. Modifying x directly changes the array element.

Question 19

Hard

Explain the row-column approach to analyzing pattern problems. How do you determine the formula for spaces and stars?

Think about what changes from row to row.

The row-column approach: (1) Identify the number of rows (outer loop, variable i). (2) For each row, count the number of spaces and the number of characters (stars/numbers). (3) Express these counts as functions of i and the total rows n. For a pyramid: spaces = n - i, stars = 2*i - 1. (4) Write inner loops based on these formulas.

Question 20

Hard

What is the output?

for (int i = 0; i < 3; i++) {
    for (int j = 0; j < 3; j++) {
        if (j == 1) break;
        cout << i << j << " ";
    }
}

break exits only the inner loop.

00 10 20

Mixed & Application Questions

Question 1

Easy

Write a program that prints even numbers from 2 to 20 using a for loop.

Start at 2, increment by 2.

for (int i = 2; i <= 20; i += 2) {
    cout << i << " ";
}

Question 2

Easy

What is the output?

int sum = 0;
for (int i = 1; i <= 5; i++) {
    sum = sum + i;
}
cout << sum;

Add 1 + 2 + 3 + 4 + 5.

15

Question 3

Medium

What is the output?

int i = 0;
while (i < 5) {
    i++;
    if (i == 3) continue;
    cout << i << " ";
}

i is incremented before the continue check.

1 2 4 5

Question 4

Medium

Write a program to check if a number N is prime using a for loop.

Check divisors from 2 to sqrt(N). If any divides N, it is not prime.

#include 
#include 
using namespace std;
int main() {
    int n;
    cin >> n;
    if (n <= 1) { cout << "Not prime" << endl; return 0; }
    bool isPrime = true;
    for (int i = 2; i <= sqrt(n); i++) {
        if (n % i == 0) { isPrime = false; break; }
    }
    cout << (isPrime ? "Prime" : "Not prime") << endl;
    return 0;
}

Question 5

Medium

What is the output?

for (int i = 2; i <= 10; i += 3) {
    cout << i << " ";
}

i starts at 2 and increases by 3: 2, 5, 8, 11.

2 5 8

Question 6

Medium

What is the output?

int i = 1;
do {
    cout << i << " ";
    i *= 2;
} while (i <= 16);

i doubles: 1, 2, 4, 8, 16, then 32.

1 2 4 8 16

Question 7

Hard

What is the output?

for (int i = 1; i <= 4; i++) {
    for (int j = 1; j <= 4 - i; j++) {
        cout << "  ";
    }
    for (int j = 1; j <= i; j++) {
        cout << i << " ";
    }
    cout << endl;
}

Row i has (4-i) double-spaces followed by i copies of the number i.

1
2 2
3 3 3
4 4 4 4

Question 8

Hard

What is the output?

int count = 0;
for (int i = 2; i <= 20; i++) {
    bool isPrime = true;
    for (int j = 2; j < i; j++) {
        if (i % j == 0) { isPrime = false; break; }
    }
    if (isPrime) count++;
}
cout << count;

Count prime numbers from 2 to 20.

8

Question 9

Hard

What is the output?

int arr[] = {3, 7, 2, 8, 1};
int n = 5;
for (int i = 0; i < n - 1; i++) {
    for (int j = 0; j < n - 1 - i; j++) {
        if (arr[j] > arr[j + 1]) {
            int temp = arr[j];
            arr[j] = arr[j + 1];
            arr[j + 1] = temp;
        }
    }
}
for (int i = 0; i < n; i++) cout << arr[i] << " ";

This is the bubble sort algorithm.

1 2 3 7 8

Question 10

Easy

Write a program that prints all numbers from 1 to 50 that are divisible by both 3 and 5.

n % 15 == 0 means divisible by both 3 and 5.

for (int i = 1; i <= 50; i++) {
    if (i % 3 == 0 && i % 5 == 0) {
        cout << i << " ";
    }
}

Question 11

Medium

What is the output?

int n = 5;
int result = 1;
for (int i = n; i >= 1; i--) {
    result *= i;
}
cout << result;

This computes 5 * 4 * 3 * 2 * 1.

120

Question 12

Hard

What is the output?

int count = 0;
for (int i = 1; i <= 100; i++) {
    if (i % 7 == 0) count++;
}
cout << count;

Count multiples of 7 from 1 to 100.

14

Question 13

Hard

What is the output?

for (int i = 1; i <= 4; i++) {
    for (int j = i; j <= 4; j++) {
        cout << j << " ";
    }
    cout << endl;
}

Row i prints numbers from i to 4.

1 2 3 4
2 3 4
3 4
4

Question 14

Hard

What is the output?

for (int i = 1; i <= 4; i++) {
    for (int j = 1; j <= i; j++) {
        cout << (i + j - 1) << " ";
    }
    cout << endl;
}

Compute (i + j - 1) for each cell.

1
2 3
3 4 5
4 5 6 7

Multiple Choice Questions

MCQ 1

Which loop is best when the number of iterations is known in advance?

A. while
B. do-while
C. for
D. Range-based for

Answer: C
C is correct. The for loop is designed for counted iterations with its init-condition-update structure.

MCQ 2

How many times does the loop body execute?
for (int i = 0; i < 10; i++) { ... }

A. 9
B. 10
C. 11
D. Infinite

Answer: B
B is correct. i takes values 0 through 9 (10 values). When i = 10, 10 < 10 is false.

MCQ 3

Which loop always executes its body at least once?

A. for
B. while
C. do-while
D. Range-based for

Answer: C
C is correct. do-while checks its condition after the body executes, guaranteeing at least one execution.

MCQ 4

What is the correct syntax for a range-based for loop in C++?

A. for (int x in arr)
B. for (auto x : arr)
C. foreach (auto x : arr)
D. for each (auto x in arr)

Answer: B
B is correct. C++11 range-based for syntax is for (type variable : container).

MCQ 5

What does the continue statement do inside a loop?

A. Exits the loop entirely
B. Skips to the next iteration
C. Pauses the loop
D. Restarts the loop from the beginning

Answer: B
B is correct. continue skips the remaining body of the current iteration and jumps to the next iteration.

MCQ 6

Which creates an infinite loop in C++?

A. for (int i = 0; i < 10; i++) {}
B. while (false) {}
C. for (;;) {}
D. do {} while (false);

Answer: C
C is correct. for (;;) has no condition, which defaults to true, creating an infinite loop.

MCQ 7

What happens if you put a semicolon after for (int i = 0; i < 5; i++); ?

A. Compilation error
B. The loop runs with an empty body
C. The loop does not run at all
D. Infinite loop

Answer: B
B is correct. The semicolon acts as an empty statement, becoming the loop body. The loop runs 5 times doing nothing.

MCQ 8

In a range-based for loop, how do you modify array elements in-place?

A. for (auto x : arr)
B. for (auto& x : arr)
C. for (const auto x : arr)
D. for (auto* x : arr)

Answer: B
B is correct. auto& creates a reference, allowing modifications to affect the original array. Plain auto creates a copy.

MCQ 9

What does break do inside a nested loop?

A. Exits all loops
B. Exits only the innermost loop
C. Exits the function
D. Causes a compilation error

Answer: B
B is correct. break exits only the innermost enclosing loop. The outer loop continues normally.

MCQ 10

What is the time complexity of this code?
for (int i = 0; i < n; i++) { for (int j = 0; j < n; j++) { ... } }

A. O(n)
B. O(n log n)
C. O(n^2)
D. O(2^n)

Answer: C
C is correct. The outer loop runs n times, and for each, the inner loop runs n times. Total: n * n = O(n^2).

MCQ 11

How many iterations does this loop execute?
for (int i = 1; i < 1000; i *= 2) { ... }

A. 500
B. 10
C. 999
D. Infinite

Answer: B
B is correct. i doubles: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512. Next: 1024 >= 1000, stop. 10 iterations (log2(1000) is approximately 10).

MCQ 12

What is the output?
int x = 0; for (int i = 0; i < 3; i++) for (int j = 0; j <= i; j++) x++; cout << x;

A. 3
B. 6
C. 9
D. 12

Answer: B
B is correct. i=0: j runs 0 to 0 (1 increment). i=1: j runs 0 to 1 (2 increments). i=2: j runs 0 to 2 (3 increments). Total: 1+2+3=6.

MCQ 13

Why is calling strlen(s) in a for loop condition a performance problem?

A. strlen() modifies the string
B. strlen() is O(n), making the loop O(n^2)
C. strlen() causes undefined behavior
D. strlen() only works with std::string

Answer: B
B is correct. strlen() scans the entire C-string to find \0, which is O(n). Calling it in every loop iteration makes the loop O(n^2) instead of O(n). Store the length in a variable before the loop.

MCQ 14

What is the output?
for (int i = 0; i < 3; i++) cout << "Hi "; cout << "Done";

A. Hi Hi Hi Done
B. Hi Hi Hi
C. Hi Done Hi Done Hi Done
D. Compilation error

First count digits, then compute sum of powers using a loop.

#include <iostream>
#include <cmath>
using namespace std;
int main() {
    int n;
    cout << "Enter a number: ";
    cin >> n;
    int digits = 0, temp = n;
    while (temp > 0) { digits++; temp /= 10; }
    int sum = 0;
    temp = n;
    while (temp > 0) {
        int d = temp % 10;
        sum += pow(d, digits);
        temp /= 10;
    }
    cout << n << (sum == n ? " is" : " is not") << " an Armstrong number" << endl;
    return 0;
}

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