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
#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" ;
}
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Java
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" );
}
}
}
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Python
my_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 :
flag = True
print ( "Yes given list has even numbers." )
break
print (flag)
IsListEven(my_list)
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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" );
}
}
}
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Javascript
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 ;
}
}
if (flag)
console.log( "YES" )
else
console.log( "NO" )
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Example 2 : Check if given number is prime or not.
Input : n = 5
Output : Yes
Input : 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
#include <iostream>
using namespace std;
bool isPrime( int n)
{
bool flag = true ;
if (n <= 1)
return false ;
for ( int i = 2; i < n; i++) {
if (n % i == 0) {
flag = false ;
break ;
}
}
return flag;
}
int main()
{
if (isPrime(13))
cout << "PRIME" ;
else
cout << "NOT A PRIME" ;
return 0;
}
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Java
import java.io.*;
class GFG {
boolean isPrime( int n)
{
boolean flag = true ;
if (n <= 1 )
return false ;
for ( int i = 2 ; i < n; i++) {
if (n % i == 0 ) {
flag = false ;
break ;
}
}
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" );
}
}
}
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Python3
num = 13
flag = False
if num = = 1 :
print (num, "NOT A PRIME" )
elif num > 1 :
for i in range ( 2 , num):
if (num % i) = = 0 :
flag = True
break
if flag:
print ( "NOT A PRIME" )
else :
print ( "PRIME" )
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C#
using System;
public class PrimeNumberExample {
public static void Main( string [] args)
{
int n, i, m = 0, flag = 0;
n = 13;
m = n / 2;
for (i = 2; i <= m; i++) {
if (n % i == 0) {
Console.Write( "NOT A PRIME" );
flag = 1;
break ;
}
}
if (flag == 0)
Console.Write( "PRIME" );
}
}
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Javascript
let number=13;
let flag = true ;
if (number === 1) {
console.log( "1 is neither prime nor composite number." );
}
else 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`);
}
}
else {
console.log( "NOT A PRIME" );
}
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