Flag variable is used as a signal in programming to let the program know that a certain condition has met. It usually acts as a boolean variable indicating a condition to be either true or false.
Example 1 : Check if an array has any even number.
Input : arr[] = {1, 3, 7, 5}
Output : No
All numbers are odd.Input : arr[] = {1, 2, 7, 5}
Output : Yes
There is one even number in the array.
We initialize a flag variable as false, then traverse the array. As soon as we find an even element, we set flag as true and break the loop. Finally we return flag.
// C++ program to check if given array is has // any even number #include <iostream> using namespace std; bool checkIfAnyEven(int arr[], int n) { bool flag = false; for (int i=0; i<n; i++) { if (arr[i] % 2 == 0) { flag = true; break; } } return flag; } int main() { int arr[] = {1, 3, 2, 5, 6, 7}; int n = sizeof(arr)/sizeof(arr[0]); if (checkIfAnyEven(arr, n)) cout << "Yes"; else cout << "No"; } |
Yes
Example 2 : Check if given number is prime or not.
Input : n = 5
Output : YesInput : n = 18
Output : No
We initialize a flag variable as true. Then we traverse through all numbers from 2 to n-1. As soon as we find a number that divides n, we set flag as false. Finally we return flag.
// C++ implementation to show the use of flag variable #include <iostream> using namespace std; // Function to return true if n is prime bool isPrime(int n) { bool flag = true; // Corner case if (n <= 1) return false; // Check from 2 to n-1 for (int i = 2; i < n; i++) { // Set flag to false and break out of the loop // if the condition is not satisfied if (n % i == 0) { flag = false; break; } } // flag variable here can tell whether the previous loop // broke without completion or it completed the execution // satisfying all the conditions return flag; } // Driver code int main() { if(isPrime(13)) cout << "PRIME"; else cout << "NOT A PRIME"; return 0; } |
PRIME
