# How do you tell if a number is prime

- 2020-06-03 07:44:57
- OfStack

Algorithms about prime Numbers are important number theory knowledge in program competition. Let's look at some algorithms that are commonly used.

Let's review a few basic concepts:

Prime: a natural number greater than 1, if it has no other factors than 1 and itself, is called prime. Prime Numbers are also called prime Numbers. On the contrary, it is called composite.

```
#include<iostream>
#include<cmath>
using namespace std;
void IsPrime(int);
int main()
{
int Input;
cout << " Please enter the number to determine: ";
cin >> Input;
IsPrime(Input);
cin.get();
cin.get();
return 0;
}
// Determine if it is prime
void IsPrime(int x)
{
if (1 == x)
{
cout << "1 Neither prime nor composite! " << endl;
return;
}
for (int i = 2; i <= sqrt(x); i++)
if (x%i == 0)
{
cout << " The number you entered is composite! " << endl;
return;
}
cout << " The number you entered is prime! " << endl;
return;
}
```