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.
CPP
// 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"; } |
Java
//Java program to check if given array is has // any even number public class GFG { boolean checkIfAnyEven(int arr[], int n) { boolean flag = false; for (int i = 0; i < n; i++) { if (arr[i] % 2 == 0) { flag = true; break; } } return flag; } public static void main(String args[]) { GFG obj = new GFG(); int arr[] = { 1, 3, 2, 5, 6, 7 }; int n = arr.length; if (obj.checkIfAnyEven(arr, n)) { System.out.println("YES"); } else { System.out.println("NO"); } }} |
Python
# Python program to check if given array has# any even numbermy_list=[1,3,5,2,7,9]def IsListEven(my_list): flag = False for i in range(len(my_list)): if my_list[i] % 2 == 0: # As pointed in comment, use != for isEven flag = True print("Yes given list has even numbers.") break print(flag)IsListEven(my_list) |
C#
using System;public class GFG { public static bool checkIfAnyEven(int[] numberArray) { foreach(var n in numberArray) { if (n % 2 != 0) return true; } return false; } public static void Main() { int[] numberArray = { 2, 4, 7, 8, 6 }; if (checkIfAnyEven(numberArray)) { Console.WriteLine("YES"); } else { Console.WriteLine("NO"); } }}// This code is contributed by Rahul Chauhan |
Javascript
// Javascript program to check if given array is has // any even number let arr = [1,3,2,5,6,7];let flag = false; { 1, 3, 2, 5, 6, 7 };for (let elem of arr) { if (elem % 2 == 0) { flag = true; break; // get out of the loop }}if (flag)console.log("YES")elseconsole.log("NO")//This code is Contributed By Rahul Chauhan |
Output
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.
CPP
// 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; } |
Java
/*package whatever //do not write package name here */// Java implementation to show the use of flag variable import java.io.*;class GFG { boolean isPrime(int n){ boolean 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;} public static void main(String[] args) { GFG obj=new GFG(); int n=13; if(obj.isPrime(n)) { System.out.println("PRIME"); }else { System.out.println("NOT A PRIME"); } }} |
Python3
# Python3 Program to check if a number is prime or notnum =13# To take input from the user#num = int(input("Enter Any Number: "))# define a flag variableflag = Falseif num == 1: print(num, "NOT A PRIME")elif num > 1: for i in range(2, num): if (num % i) == 0: flag = True break # check if flag is True if flag: print("NOT A PRIME") else: print("PRIME") #This code is contributed By Rahul Chauhan |
C#
// C# implementation to show the use of flag variableusing System;public class PrimeNumberExample { public static void Main(string[] args) { int n, i, m = 0, flag = 0; n = 13; m = n / 2; // Check from 2 to n-1 for (i = 2; i <= m; i++) { // Set flag to false and break out of the loop // if the condition is not satisfied if (n % i == 0) { Console.Write("NOT A PRIME"); flag = 1; break; } } if (flag == 0) Console.Write("PRIME"); }} |
Javascript
//JAVASCRIPT PROGRAM to check if a number is prime or notlet number=13;let flag = true;// check if number is equal to 1if (number === 1) { console.log("1 is neither prime nor composite number.");}// check if number is greater than 1else if (number > 1) { for (let i = 2; i < number; i++) { if (number % i == 0) { flag = false; break; } } if (flag) { console.log(`PRIME`); } else { console.log(`NOT A PRIME NUMBER`); }}// check if number is less than 1else { console.log("NOT A PRIME");}// This code is contributed By Rahul Chauhan |
Output
PRIME
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