primeComposite.cpp

#include<iostream>
using namespace std;

void primeFun(int n){
	bool isPrime[n+1];	//creating an array of size n+1
	for(int i=0;i<=n;i++){	//making boolean for all values as true ,as it will be used-
		isPrime[i]=true;	//as prime by default (intial assumption for convenience)
	}
	isPrime[0]=false;	//*0* nor prime nor composite 
	isPrime[1]=false;	//*1* nor prime nor composite
	for(int i=2;i*i<=n;i++){
		if(isPrime[i]==true){
			for(int j=i*i;j<=n;j+=i){	//This is puting value of i's multiple's as false-
				isPrime[j]=false;	// as they will be composite, eg: 2 mltiple 4,6,8....;	3:3,6,9,...		
			}
		}
	}
	system("CLS");	//to clear screen 
	cout<<0<<" : "<<"nor prime nor composite\n";
	cout<<0<<" : "<<"nor prime nor composite\n";
	for(int i=2;i<=n;i++){

		cout<<i<<" : ";
		if(isPrime[i]==true){
			cout<<"prime"<<endl;
		}else{
			cout<<"composite"<<endl;
		}	
//		cout<<i<<" : "<<isPrime[i]<<"\n"; //uncomment for output
	}

}

int main(){
	int n;
	cin >> n;
	primeFun(n);	//
	return 0;
}