In this program, we will make a c++ program to print prime numbers upto n.

• Prime numbers up to n
• Prime numbers between 1 to 100
• Prime numbers in a given range

Basic knowledge required: for-loop & if-else.

## C++ program to print prime numbers upto n

We have to print prime numbers from 1 to n, where n is the upper range. The user gives the upper range according to their choice.

```#include<iostream>
using namespace std;
int main()
{
int n,i,j;
cout<<"Enter upper range:";
cin>>n;
cout<<"n Prime Numbers from 1 to "<<n<<": ";
for(i=1;i<=n;i++)
{
for(j=2;j<=i;j++)
{
if(i%j==0)
break;
}
if(i==j)
cout<<j<<" ";
}
return 0;
}```

Output:
Enter upper range:50
Prime Numbers from 1 to 50: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 ## Print prime numbers between 1 and 100

This program will print prime numbers from 1 to 100.

```#include<iostream>
using namespace std;
int main()
{
int i,j;
cout<<"n Prime Numbers from 1 to 100: ";
for(i=1;i<=100;i++)
{
for(j=2;j<=i;j++)
{
if(i%j==0)
break;
}
if(i==j)
cout<<j<<" ";
}
return 0;
}```
Output:
Prime Numbers from 1 to 100: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97

## C++ program to print prime numbers in a given range

In this program, we have to display prime numbers in a given range, i.e., lower and upper limits. The lower limit, as well as the upper limit, is provided by the user according to their choice.

```#include<iostream>
using namespace std;
int main()
{
int l,u,i,j;
cout<<"Enter lower limit:";
cin>>l;
cout<<"Enter upper limit:";
cin>>u;
cout<<"n Prime Numbers from "<<l<<" to "<<u<<": ";
for(i=l;i<=u;i++)
{
for(j=2;j<=i;j++)
{
if(i%j==0)
break;
}
if(i==j)
cout<<j<<" ";
}
return 0;
}```
Output:
Enter lower limit:10
Enter upper limit:50
Prime Numbers from 10 to 50: 11 13 17 19 23 29 31 37 41 43 47

## Find Prime Numbers From 1 to N

Given a number N, find number of primes in the range [1,N].

```#include<bits/stdc++.h>
using namespace std;
int checkPrime(int n)
{
//factors of 10 are 1,2,5,10
/* 10-1*10, 2*5,5*2,10*1
so we can run loop from 1 to sqrt(n)*/
//factors of 7 - 1,7
//for prime numbers, there are only two factors
int c=0;
for(int i=1;i*i<=n;i++)
{
if(n%i==0)
{
if(i*i==n)
c+=1;
else
c+=2;
}
}
if(c==2)
return true;
return false;
}
int main(){```

int n;
cin>>n;
int count=0;
for(int i=1;i<=n;i++)
{
if(checkPrime(i))
{
count++;
}
}
cout<<count<<endl;
return 0;
}

Input: 6
Output: 3
There are three prime numbers from 1 to 6 {2,3,5}.

## How do you print all prime numbers in C++ using a do-while loop?

```#include<iostream>
using namespace std;
int main()
{
int n,i,j;
cout<<"Enter upper range:";
cin>>n;
cout<<"n Prime Numbers from 1 to "<<n<<": ";
for(i=1;i<=n;i++)
{
int j=2;
do
{
if(i%j==0)
break;
j++;
}while(j<=i);
if(i==j)
cout<<j<<" ";
}
return 0;
}
```