# Check if a number is prime or not

Discussion in 'C++' started by aadilprabhakar, Nov 27, 2008.

1. ### aadilprabhakarNew Member

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### To check if the number is prime or not.

Code:
```
/*
To check if an integer is prime or not
*/

#include<iostream.h>
#include<conio.h>
void main()
{[INDENT]     int num,i;

clrscr();

cout<< "Please enter the number ";
cin >> num;
i =2 ;

while(1){[INDENT]        if (num%i==0) {[INDENT]         if(num == i){[INDENT]             cout << "Prime Number";
break;
[/INDENT][/INDENT][INDENT]         } else {[INDENT]cout << "Not Prime";
break;
[/INDENT]}
[/INDENT]} else {[INDENT]         i++;
[/INDENT]}
[/INDENT]}
[/INDENT]}
```

2. ### shabbirAdministratorStaff Member

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You don't need to loop till i but even i/2 or square root of i is also sufficient.

3. ### back from retirementNew Member

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Yes....the actual is the square root of i. You can use the standard function sqrt(); for that purpose.

4. ### skp819New Member

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A simple program is here. to chech a number is prime or not.
Code:
```void main()
{
int a,b,i;
cout<<"\n enter the no: ";
cin>>a;
for(i=2;i<=a;i++)
{
rem=a%i;
if(rem==0)
{
cout<<"\nNo is not prime: ";
}
else
{
cout<<"\nNo is  prime:";
}
}
}```

Last edited by a moderator: Dec 19, 2008