Top 100 C++ Coding Interview Questions and Answers [2025 Updated]

// C++ Program to check whether a number is positive or
// negative
#include <iostream>
using namespace std;

int main()
{
    int number;
    number = -100;
    if (number >= 0) {
        cout << number << " is a positive number." << endl;
    }
    else {
        cout << number << " is a negative number." << endl;
    }
    return 0;
}

// C++ program to find greatest
// among three numbers using
#include <iostream>
using namespace std;

int main()
{
    int a = 10, b = 20, c = 30;

    cout << "The Greatest Among Three Numbers is : ";

    if (a >= b && a >= c) {
        cout << a << endl;
    }
    else if (b >= a && b >= c) {
        cout << b << endl;
    }
    else {
        cout << c << endl;
    }

    return 0;
}

// C++ program to check
// for even or odd
#include <iostream>
using namespace std;

// Returns true if n is
// even, else odd
bool isEven(int n) { return (n % 2 == 0); }

// Driver code
int main()
{
    int n = 247;
    if (isEven(n) == true) {
        cout << "Even" << endl;
    }
    else {
        cout << "Odd";
    }

    return 0;
}

// C++ Program to find ASCII value of a character
#include <iostream>
using namespace std;

int main()
{
    char ch;

    ch = 'A';

    cout << "The ASCII value of " << ch << " is " << int(ch)
         << endl;

    return 0;
}

// C++ Program to print whether a character is vowel or not
#include <cctype>
#include <iostream>
using namespace std;

int main()
{
    char ch = 'e';

    if (isalpha(ch)) {
        if (ch == 'a' || ch == 'e' || ch == 'i' || ch == 'o'
            || ch == 'u' || ch == 'A' || ch == 'E'
            || ch == 'I' || ch == 'O' || ch == 'U') {
            cout << ch << " is a vowel." << endl;
        }
        else {
            cout << ch << " is a consonant." << endl;
        }
    }
    else {
        cout << ch << " is not an alphabet." << endl;
    }

    return 0;
}

// C++ program to print whether a character is an alphabet
// or not
#include <cctype>
#include <iostream>
using namespace std;

int main()
{
    char ch;

    ch = 'a';

    if (isalpha(ch)) {
        cout << ch << " is an alphabet." << endl;
    }
    else {
        cout << ch << " is not an alphabet." << endl;
    }

    return 0;
}

// C++ Program to find the length of a string without using
// strlen()
#include <cstring>
#include <iostream>
using namespace std;

int main()
{
    string str = "GeeksforGeeks";
    int length = 0;

    for (int i = 0; str[i] != '\0'; i++) {
        length++;
    }

    cout << "The length of the string is: " << length
         << endl;

    return 0;
}

// C++ Program to toggle string
#include <cstring>
#include <iostream>
using namespace std;

int main()
{
    string str = "GeeksforGeeks";

    for (int i = 0; str[i] != '\0'; i++) {
        if (islower(str[i])) {
            str[i] = toupper(str[i]);
        }
        else if (isupper(str[i])) {
            str[i] = tolower(str[i]);
        }
    }

    cout << "Toggled string: " << str << endl;

    return 0;
}

// C++ Program to count the number of vowels
#include <cstring>
#include <iostream>
using namespace std;

int main()
{
    string str = "GeeksforGeeks to the moon";
    int vowels = 0;

    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] == 'a' || str[i] == 'e' || str[i] == 'i'
            || str[i] == 'o' || str[i] == 'u'
            || str[i] == 'A' || str[i] == 'E'
            || str[i] == 'I' || str[i] == 'O'
            || str[i] == 'U') {
            vowels++;
        }
    }

    cout << "Number of vowels in the string: " << vowels
         << endl;

    return 0;
}

// C++ Program to remove the vowels from a string
#include <cstring>
#include <iostream>
using namespace std;

int main()
{
    int j = 0;

    string str = "GeeksforGeeks";

    for (int i = 0; str[i] != '\0'; i++) {
        if (str[i] != 'a' && str[i] != 'e' && str[i] != 'i'
            && str[i] != 'o' && str[i] != 'u'
            && str[i] != 'A' && str[i] != 'E'
            && str[i] != 'I' && str[i] != 'O'
            && str[i] != 'U') {
            str[j++] = str[i];
        }
    }
    while (j < str.size()) {

        str[j] = '\0';

        j++;
    }
    cout << "String without vowels: " << str << endl;

    return 0;
}

// C++ Programto remove all characters from a string except
// alphabets
#include <cctype>
#include <iostream>
#include <string>

using namespace std;

string remove_non_alphabets(string str)
{
    string result = "";
    for (char c : str) {
        if (isalpha(c)) {
            result += c;
        }
    }
    return result;
}

int main()
{
    string str = "Gee$ksfor$geeks";

    cout << "Alphabets only: " << remove_non_alphabets(str)
         << endl;

    return 0;
}

// C++ Program to remove spaces from a string
#include <iostream>
#include <string>

using namespace std;

string remove_spaces(string str)
{
    string result = "";
    for (char c : str) {
        if (c != ' ') {
            result += c;
        }
    }
    return result;
}

int main()
{
    string str = "Gfg to the moon";

    cout << "Without spaces: " << remove_spaces(str)
         << endl;

    return 0;
}

// C++ program to find
// Sum of first
// n natural numbers.
#include <iostream>
using namespace std;

// Function to find sum
int findSum(int n)
{
    int sum = 0;
    for (int i = 1; i <= n; i++)
        sum = sum + i;
    return sum;
}

int main()
{
    int n = 7;
    cout << findSum(n);
    return 0;
}

// C++ program to find factorial using loops
#include <bits/stdc++.h>
using namespace std;

// function to find factorial
int factorial(int n)
{
    int fact = 1;
    while (n > 1) {
        fact *= n;
        n--;
    }

    return fact;
}

// driver code
int main()
{
    int num = 5;

    cout << factorial(num);

    return 0;
}

// C++ program to check if a given
// year is leap year or not
#include <iostream>
using namespace std;

bool checkYear(int year)
{
    // leap year
    if (year % 400 == 0)
        return true;

    // Not leap year
    if (year % 100 == 0)
        return false;

    // leap year
    if (year % 4 == 0)
        return true;

    // Not leap year
    return false;
}

int main()
{
    int year = 2000;

    if (checkYear(year))
        cout << "Leap Year";
    else
        cout << "Not a Leap Year";
    return 0;
}

// C++ program to check if a
// Number is prime
#include <iostream>
using namespace std;

bool isPrime(int n)
{
    // base condition
    if (n <= 1)
        return false;

    // Check from 2 to n-1
    for (int i = 2; i < n; i++)
        if (n % i == 0)
            return false;

    return true;
}

int main()
{
    isPrime(21) ? cout << " true\n" : cout << " false\n";
    isPrime(17) ? cout << " true\n" : cout << " false\n";
    return 0;
}

// C++ program to check if a
// number is Palindrome or not
#include <iostream>
using namespace std;

// Function to check Palindrome
bool checkPalindrome(int n)
{
    int ans = 0;
    int temp = n;
    while (temp != 0) {
        ans = (ans * 10) + (temp % 10);
        temp = temp / 10;
    }

    return (ans == n);
}

int main()
{
    int n = 12321;

    if (checkPalindrome(n) == 1) {
        cout << "Yes\n";
    }
    else {
        cout << "No\n";
    }

    return 0;
}

// C++ Program to check
// if number is Armstrong
// or not
#include <iostream>
using namespace std;

int main()
{
    int n = 153;
    int temp = n;
    int ans = 0;

    // function to calculate
    // the sum of individual digits
    while (n > 0) {

        int rem = n % 10;
        ans = (ans) + (rem * rem * rem);
        n = n / 10;
    }

    // condition to check
    if (temp == ans) {
        cout << ("Yes, it is Armstrong Number");
    }
    else {
        cout << ("No, it is not an Armstrong Number");
    }
    return 0;
}

// C++ Program to Find the
// Nth Term of the Fibonacci Series
#include <iostream>
using namespace std;

int fib(int n)
{
    int first = 0, second = 1, ans;
    if (n == 0)
        return first;

    for (int i = 2; i <= n; i++) {
        ans = first + second;
        first = second;
        second = ans;
    }

    return ans;
}

int main()
{
    int n = 13;

    cout << fib(n);
    return 0;
}

// C++ program to find
// GCD of two numbers
#include <iostream>

using namespace std;

// Function to return gcd of a and b
int gcd(int a, int b)
{
    int result = min(a, b);

    while (result > 0) {
        if (a % result == 0 && b % result == 0) {
            break;
        }
        result--;
    }

    return result;
}

int main()
{
    int a = 54, b = 33;

    cout << "GCD: " << gcd(a, b);

    return 0;
}

// C++ program to
// Find LCM of two numbers
#include <iostream>
using namespace std;

long long gcd(long long int a, long long int b)
{
    if (b == 0)
        return a;
    return gcd(b, a % b);
}

// Function to return LCM of two numbers
long long lcm(int a, int b)
{
    long long result = (a / gcd(a, b)) * b;
    return result;
}

int main()
{
    int a = 24, b = 13;
    cout << "LCM : " << lcm(a, b);
    return 0;
}

// C++ program to find
// Roots of a quadratic equation
#include <iostream>
#include <math.h>
using namespace std;

// Prints roots of quadratic equation ax*2 + bx + c
void findRoots(int a, int b, int c)
{
    // If a is 0, then equation is not quadratic
    if (a == 0) {
        cout << "Invalid";
        return;
    }

    // Formulae to calculate D
    int d = b * b - 4 * a * c;

    // Formulae to calculate
    // square root of D
    double sqrt_val = sqrt(abs(d));

    // Conditons for checking root
    if (d > 0) {
        cout << "Roots are real and different \n";
        cout << (double)(-b + sqrt_val) / (2 * a) << "\n"
             << (double)(-b - sqrt_val) / (2 * a);
    }
    else if (d == 0) {
        cout << "Roots are real and same \n";
        cout << -(double)b / (2 * a);
    }
    else {
        cout << "Roots are complex \n";
        cout << -(double)b / (2 * a) << " + i"
             << sqrt_val / (2 * a) << "\n"
             << -(double)b / (2 * a) << " - i"
             << sqrt_val / (2 * a);
    }
}

int main()
{
    int a = 1, b = 4, c = 4;

    findRoots(a, b, c);

    return 0;
}

// C++ code to for
// Finding the minimum
// And maximum of the array
#include <iostream>
using namespace std;

// Function to find the minimum
// and maximum of the array
void findMinMax(int arr[], int n)
{
    int mini = arr[0];
    int maxi = arr[0];

    for (int i = 0; i < n; i++) {
        if (arr[i] < mini) {
            mini = arr[i];
        }
        else if (arr[i] > maxi) {
            maxi = arr[i];
        }
    }

    cout << "Min: " << mini << endl;
    cout << "Max: " << maxi << endl;
}

int main()
{
    int arr[] = { 1, 2, 3, 4, 5 };
    int N = sizeof(arr) / sizeof(arr[0]);

    findMinMax(arr, N);

    return 0;
}

// C++ program to find
// Second smallest elements
#include <climits>
#include <iostream>
using namespace std;

void print2Smallest(int arr[], int n)
{
    int first, second;

    if (n < 2) {
        cout << " Invalid Input ";
        return;
    }

    first = second = INT_MAX;
    for (int i = 0; i < n; i++) {
        // If current element is smaller than first
        // Then update both first and second
        if (arr[i] < first) {
            second = first;
            first = arr[i];
        }

        // If arr[i] is in between first and second
        // Then update second
        else if (arr[i] < second && arr[i] != first)
            second = arr[i];
    }
    if (second == INT_MAX)
        cout << "There is no second smallest element\n";
    else
        cout << " Second smallest element is " << second
             << endl;
}

int main()
{
    int arr[] = { 21, 3, 15, 41, 34, 10 };
    int n = sizeof(arr) / sizeof(arr[0]);

    print2Smallest(arr, n);

    return 0;
}

// C++ Program to calculate
// sum of elements in an array
#include <iostream>
using namespace std;

int sum(int arr[], int n)
{
    int sum = 0;

    for (int i = 0; i < n; i++)
        sum += arr[i];

    return sum;
}

int main()
{
    int arr[] = { 1, 23, 54, 12, 9 };
    int n = sizeof(arr) / sizeof(arr[0]);

    cout << "Sum: " << sum(arr, n);

    return 0;
}

// C++ program for checking
// if it is Palindrome or not
#include <iostream>
using namespace std;

string isPalindrome(string S)
{
    for (int i = 0; i < S.length() / 2; i++) {
        if (S[i] != S[S.length() - i - 1]) {
            return "No";
        }
    }

    return "Yes";
}

int main()
{
    string S = "GeekeeG";

    cout << isPalindrome(S);

    return 0;
}

// C++ program to check if two strings
// Are anagrams of each other
#include <iostream>
using namespace std;

#define NO_OF_CHARS 256

bool areAnagram(char* str1, char* str2)
{
    // Create 2 count arrays and initialize all values as 0
    int count1[NO_OF_CHARS] = { 0 };
    int count2[NO_OF_CHARS] = { 0 };
    int i;

    // For each character in input strings, increment count
    // in the corresponding count array
    for (i = 0; str1[i] && str2[i]; i++) {
        count1[str1[i]]++;
        count2[str2[i]]++;
    }

    if (str1[i] || str2[i])
        return false;

    // Compare count arrays
    for (i = 0; i < NO_OF_CHARS; i++)
        if (count1[i] != count2[i])
            return false;

    return true;
}

int main()
{
    char str1[] = "Geek";
    char str2[] = "for";

    if (areAnagram(str1, str2))
        cout << "The two strings are anagram of each other";
    else
        cout << "The two strings are not anagram of each "
                "other";

    return 0;
}

// C++ program to print
// Diamond shape
#include <iostream>
using namespace std;

void printDiamond(int n)
{
    int space = n - 1;

    for (int i = 0; i < n; i++) {
        for (int j = 0; j < space; j++)
            cout << " ";

        // Print i+1 stars
        for (int j = 0; j <= i; j++)
            cout << "* ";

        cout << endl;
        space--;
    }

    space = 0;

    // run loop (parent loop)
    for (int i = n; i > 0; i--) {
        for (int j = 0; j < space; j++)
            cout << " ";

        // Print i stars
        for (int j = 0; j < i; j++)
            cout << "* ";

        cout << endl;
        space++;
    }
}

int main()
{
    printDiamond(5);
    return 0;
}

// C++ Program to
// Print Pyramid pattern
#include <iostream>
using namespace std;

void pattern(int n)
{
    int k = 2 * n - 2;

    for (int i = 0; i < n; i++) {

        for (int j = 0; j < k; j++)
            cout << " ";

        k = k - 1;
        for (int j = 0; j <= i; j++) {
            // Printing stars
            cout << "* ";
        }
        cout << endl;
    }
}

int main()
{
    int n = 5;

    pattern(n);
    return 0;
}

// C Program to print hourglass pattern
#include <iostream>
using namespace std;

// function to print hourglass pattern
void hourglass(int rows)
{

    // first outer loop to iterate each row
    for (int i = 0; i < 2 * rows - 1; i++) {

        // assigning comparator
        int comp;
        if (i < rows) {
            comp = 2 * i + 1;
        }
        else {
            comp = 2 * (2 * rows - i) - 3;
        }

        // first inner loop to print leading spaces
        for (int j = 0; j < comp; j++) {
            cout << ' ';
        }

        // second inner loop to print star *
        for (int k = 0; k < 2 * rows - comp; k++) {
            cout << "* ";
        }
        cout << '\n';
    }
}

int main()
{
    hourglass(5);
    return 0;
}

// C++ Program to print
// star pattern given
#include <iostream>
using namespace std;

void pattern(int n)
{
    for (int i = 0; i <= n; i++) {
        for (int j = 0; j <= i; j++) {
            cout << "* ";
        }

        int spaces = 2 * (n - i);
        for (int j = 0; j < spaces; j++) {
            cout << "  ";
        }

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

        cout << endl;
    }

    // Printing bottom part.
    for (int i = n - 1; i >= 0; i--) {

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

        int spaces = 2 * (n - i);
        for (int j = 0; j < spaces; j++) {
            cout << "  ";
        }

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

        cout << endl;
    }
}

int main()
{
    int n = 5;

    pattern(n);

    return 0;
}

// C++ Program to print a simple pyramid
#include <iostream>
using namespace std;

int main()
{
    int rows = 5;

    for (int i = 1; i <= rows; i++) {
        for (int j = rows; j >= i; j--) {
            cout << " ";
        }
        for (int k = 1; k <= (2 * i - 1); k++) {
            cout << "*";
        }
        cout << endl;
    }

    return 0;
}

// C++ Program to print inverted pyramid
#include <iostream>
using namespace std;

int main()
{
    int rows = 5;

    for (int i = rows; i >= 1; i--) {
        for (int j = rows; j > i; j--) {
            cout << " ";
        }
        for (int k = 1; k <= (2 * i - 1); k++) {
            cout << "*";
        }
        cout << endl;
    }

    return 0;
}

// C++ Program to print a triangle star patter
#include <iostream>
using namespace std;

int main()
{
    int rows;

    rows = 5;

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

    return 0;
}

// C Program to print the Floyd's Triangle
#include <stdio.h>

int main()
{
    int rows = 4;
    int n = 1;

    // outer loop to print all rows
    for (int i = 0; i < rows; i++) {

        // innter loop to print abphabet in each row
        for (int j = 0; j <= i; j++) {
            printf("%d ", n++);
        }
        printf("\n");
    }
    return 0;
}

// C++ program to print
// Pascal’s Triangle
#include <iostream>
using namespace std;

void printPascal(int n)
{

    int arr[n][n];

    for (int line = 0; line < n; line++) {
        // Every line has number of integers
        // equal to line number
        for (int i = 0; i <= line; i++) {
            // First and last values in every row are 1
            if (line == i || i == 0)
                arr[line][i] = 1;
            else
                arr[line][i] = arr[line - 1][i - 1]
                               + arr[line - 1][i];
            cout << arr[line][i] << " ";
        }
        cout << "\n";
    }
}

int main()
{
    int n = 6;
    printPascal(n);
    return 0;
}

// C++ Program to reversea string
#include <cstring>
#include <iostream>
using namespace std;

int main()
{

    int len;

    string str = "GeeksforGeeks";

    len = str.size();

    cout << "Reverse of the string: ";
    for (int i = len - 1; i >= 0; i--) {
        cout << str[i];
    }
    cout << endl;

    return 0;
}

// C++ Program to
// Reverse string using
// recursion
#include <iostream>
using namespace std;

void reverse_str(string& s, int n, int i)
{
    if (n <= i) {
        return;
    }

    swap(s[i], s[n]);
    reverse_str(s, n - 1, i + 1);
}

int main()
{
    string str = "GeeksforGeeks";
    reverse_str(str, str.length() - 1, 0);
    cout << str << endl;
}

// C++ program to check
// Whether a given number
// Is palindrome or not
#include <bits/stdc++.h>
using namespace std;

bool isPalRec(char str[], int s, int n)
{
    // If there is only one character
    if (s == n)
        return true;

    // If first and last
    // characters do not match
    if (str[s] != str[n])
        return false;

    if (s < n + 1)
        return isPalRec(str, s + 1, n - 1);

    return true;
}

bool isPalindrome(char str[])
{
    int n = strlen(str);

    if (n == 0)
        return true;

    return isPalRec(str, 0, n - 1);
}

int main()
{
    char str[] = "GeeKeeG";

    if (isPalindrome(str))
        cout << "Yes";
    else
        cout << "No";

    return 0;
}

// C++ Program for calculating
// the length of string
#include <iostream>
using namespace std;

int cal(char* str)
{
    // base condition
    if (*str == '\0')
        return 0;
    else
        return 1 + cal(str + 1);
}

int main()
{
    char str[] = "GeeksforGeeks";
    cout << cal(str);
    return 0;
}

// C++ program to calculate
// Factorial of given number
#include <iostream>
using namespace std;

unsigned long long factorial(unsigned long long n)
{
    if (n == 0 || n == 1)
        return 1;
    return n * factorial(n - 1);
}

int main()
{
    unsigned long long num = 15;

    cout << "Factorial of " << num << " is "
         << factorial(num) << endl;

    return 0;
}

// C++ Program to count the sume of numbers in a string
#include <iostream>
#include <sstream>
#include <string>

using namespace std;

int sum_of_numbers(string str)
{
    int sum = 0;
    for (char ch : str) {
        if (isdigit(ch)) {
            sum += ch - '0';
        }
    }
    return sum;
}

int main()
{
    string str;

    str = "1234";

    cout << "Sum of numbers: " << sum_of_numbers(str)
         << endl;

    return 0;
}

// C++ program to print all natural numbers upto
// N without using semi-colon
#include <iostream>

using namespace std;
#define N 10

int main()
{
    static int x = 1;
    if (cout << x << " " && x++ < N && main()) {
    }
    return 0;
}

// C++ program to check
// If two numbers are equal
#include <iostream>
using namespace std;

int main()
{
    int x = 3;
    int y = 4;

    cout << "X : " << x << endl;
    cout << "Y : " << y << endl;

    x = x + y;
    y = x - y;
    x = x - y;

    cout << endl;
    cout << "After:" << endl;

    cout << "X : " << x << endl;
    cout << "Y : " << y << endl;

    return 0;
}

// C++ program to print maximum value of
// unsigned int.
#include <iostream>

using namespace std;

int main()
{
    unsigned int max;
    max = 0;
    max = ~max;

    cout << "Max value possible : " << max;

    return 0;
}

// C++ Program to equality of
// Two numbers without using
// Arithmetic or comparison operator
#include <iostream>
using namespace std;

int main()
{
    int a = 10, b = 10;

    if (a ^ b)
        cout << "Not-Equal";
    else
        cout << "Equal";

    return 0;
}

// C++ program to find
// maximum and minimum of
// Two numbers without using
// loop and conditions
#include <iostream>

using namespace std;

int main()
{
    int a = 5, b = 10;

    cout << "max :" << (((a + b) + abs(a - b)) / 2) << endl;
    cout << "min :" << (((a + b) - abs(a - b)) / 2) << endl;

    return 0;
}

// C++ Program to convert ocatal to decimal
#include <cmath>
#include <iostream>

using namespace std;

int main()
{
    int oct, dec = 0, place = 0;
    // 67 is an octal number with binary equivalent 110000
    oct = 67;

    int temp = oct;
    while (temp) {
        int lastDigit = temp % 10;
        temp /= 10;
        dec += lastDigit * pow(8, place);
        ++place;
    }

    cout << "Decimal equivalent is: " << dec << endl;

    return 0;
}