﻿ C++ Exercises: Find prime number within a range - w3resource # C++ Exercises: Find prime number within a range

## C++ For Loop: Exercise-6 with Solution

Write a program in C++ to find prime number within a range.

Sample Solution:

C++ Code:

``````#include <iostream>
#include<math.h>
using namespace std;
int main()
{
int num1,num2;
int fnd=0,ctr=0;
cout << "\n\n Find prime number within a range:\n";
cout << "--------------------------------------\n";
cout << " Input number for starting range: ";
cin>> num1;
cout << " Input number for ending range: ";
cin>> num2;

cout << "\n The prime numbers between "<<num1<<" and "<<num2<<" are:"<<endl;
for(int i=num1;i<=num2;i++)
{
for(int j=2;j<=sqrt(i);j++)
{
if(i%j==0)
ctr++;
}
if(ctr==0&&i!=1)
{ fnd++;
cout<<i<<" ";

}
ctr=0;
}
cout<<"\n\n The total number of prime numbers between "<<num1<<" to "<<num2<<" is: "<<fnd<<endl;
return 1;
}
``````

Sample Output:

``` Find prime number within a range:
--------------------------------------
Input number for starting range: 1
Input number for ending range: 100

The prime numbers between 1 and 100 are:
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

The total number of prime numbers between 1 to 100 is: 25
```

Flowchart: C++ Code Editor:

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## C++ Programming: Tips of the Day

What is a smart pointer and when should I use one?

This answer is rather old, and so describes what was 'good' at the time, which was smart pointers provided by the Boost library. Since C++11, the standard library has provided sufficient smart pointers types, and so you should favour the use of std::unique_ptr, std::shared_ptr and std::weak_ptr.

There was also std::auto_ptr. It was very much like a scoped pointer, except that it also had the "special" dangerous ability to be copied - which also unexpectedly transfers ownership.

It was deprecated in C++11 and removed in C++17, so you shouldn't use it.

```std::auto_ptr<MyObject> p1 (new MyObject());
std::auto_ptr<MyObject> p2 = p1; // Copy and transfer ownership.
// p1 gets set to empty!
p2->DoSomething(); // Works.
p1->DoSomething(); // Oh oh. Hopefully raises some NULL pointer exception.
```

Ref : https://bit.ly/3mc9GHE