print prime number upto number N - c++14

Question

#include<iostream>
using namespace std;
int main()
{
int N;
cin>>N;
int flag=1;
for(int i=2;i<=N;i++){
for(int j=2;j<i;j++){
if(i%j==0){flag=0;break;}
break;
}
if(flag==1){cout<<i<<" ";}
}
return 0;
}
program is to print prime numbers upto input number N with seperated space
ex - N=9, my o/p -2 3,
expected o/p - 2 3 5 7
help

Answer 1

Just initial flag = 1 after every iteration
#include<iostream>
using namespace std;
int main()
{
int N;
cin>>N;
int flag=1;
for(int i=2;i<=N;i++){
flag=1;
for(int j=2;j<i;j++){
if(i%j==0){flag=0;break;}
break;
}
if(flag==1){cout<<i<<" ";}
}
return 0;
}

Answer 2

You've got at least two issues:
You never reset flag to 1. So as soon as a non-prime is found, everything is non-prime. You want to set it back to 1 each time you loop in the outer loop.
You break out of your inner loop unconditionally (j is never anything but 2), so you're actually testing for "is odd" not "is prime". Only break if you've confirmed it's not prime.
Fix that, and the code works:
#include<iostream>
using namespace std;
int main() {
int N;
cin>>N;
for(int i=2;i<=N;i++){
int flag=1; // Set each loop
for(int j=2;j<i;j++){
if(i%j==0){
flag=0;
break; // Only break when confirmed composite
}
// no break otherwise
}
if(flag==1){
cout<<i<<" ";
}
}
return 0;
}
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