C++ Important Programs
Classic C++ Programs
These programs cover the most commonly asked C++ problems in interviews and competitive programming. Each demonstrates key language features.
#include <iostream>
using namespace std;
// Iterative Fibonacci
void fibonacci(int n) {
long long a = 0, b = 1;
cout << "Fibonacci(" << n << "): ";
for (int i = 0; i < n; i++) {
cout << a << " ";
long long c = a + b;
a = b;
b = c;
}
cout << endl;
}
// Recursive Fibonacci
long long fibRec(int n) {
if (n <= 1) return n;
return fibRec(n-1) + fibRec(n-2);
}
int main() {
fibonacci(10); // 0 1 1 2 3 5 8 13 21 34
cout << "fib(10) = " << fibRec(10) << endl; // 55
return 0;
}#include <iostream>
using namespace std;
long long factorial(int n) {
if (n <= 1) return 1;
return n * factorial(n - 1);
}
int main() {
for (int i = 0; i <= 12; i++) {
cout << i << "! = " << factorial(i) << endl;
}
return 0;
}#include <iostream>
#include <cmath>
using namespace std;
bool isPrime(int n) {
if (n < 2) return false;
if (n == 2) return true;
if (n % 2 == 0) return false;
for (int i = 3; i <= sqrt(n); i += 2) {
if (n % i == 0) return false;
}
return true;
}
int main() {
cout << "Primes up to 50: ";
for (int i = 2; i <= 50; i++) {
if (isPrime(i)) cout << i << " ";
}
cout << endl;
// 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47
return 0;
}#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
bool isPalindrome(const string &s) {
string rev = s;
reverse(rev.begin(), rev.end());
return s == rev;
}
bool isNumPalindrome(int n) {
int original = n, reversed = 0;
while (n > 0) {
reversed = reversed * 10 + n % 10;
n /= 10;
}
return original == reversed;
}
int main() {
cout << boolalpha;
cout << isPalindrome("racecar") << endl; // true
cout << isPalindrome("hello") << endl; // false
cout << isNumPalindrome(121) << endl; // true
cout << isNumPalindrome(123) << endl; // false
return 0;
}#include <iostream>
#include <string>
#include <algorithm>
using namespace std;
bool isAnagram(string a, string b) {
sort(a.begin(), a.end());
sort(b.begin(), b.end());
return a == b;
}
int main() {
cout << boolalpha;
cout << isAnagram("listen", "silent") << endl; // true
cout << isAnagram("hello", "world") << endl; // false
cout << isAnagram("triangle", "integral") << endl; // true
return 0;
}#include <iostream>
#include <vector>
using namespace std;
void bubbleSort(vector<int> &v) {
int n = v.size();
for (int i = 0; i < n-1; i++) {
bool swapped = false;
for (int j = 0; j < n-i-1; j++) {
if (v[j] > v[j+1]) {
swap(v[j], v[j+1]);
swapped = true;
}
}
if (!swapped) break;
}
}
int binarySearch(const vector<int> &v, int target) {
int lo = 0, hi = v.size() - 1;
while (lo <= hi) {
int mid = lo + (hi - lo) / 2;
if (v[mid] == target) return mid;
if (v[mid] < target) lo = mid + 1;
else hi = mid - 1;
}
return -1;
}
int main() {
vector<int> v = {64, 34, 25, 12, 22, 11, 90};
bubbleSort(v);
for (int n : v) cout << n << " "; // 11 12 22 25 34 64 90
cout << endl;
cout << "Index of 25: " << binarySearch(v, 25) << endl; // 2
return 0;
}#include <iostream>
using namespace std;
void multiplyMatrix(int A[][3], int B[][3], int C[][3], int n) {
for (int i = 0; i < n; i++)
for (int j = 0; j < n; j++) {
C[i][j] = 0;
for (int k = 0; k < n; k++)
C[i][j] += A[i][k] * B[k][j];
}
}
int main() {
int A[3][3] = {{1,2,3},{4,5,6},{7,8,9}};
int B[3][3] = {{9,8,7},{6,5,4},{3,2,1}};
int C[3][3];
multiplyMatrix(A, B, C, 3);
cout << "A x B:" << endl;
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) cout << C[i][j] << "\t";
cout << endl;
}
return 0;
}
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