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Check if a number is prime or not

### 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() {    int num,i;     clrscr();     cout<< "Please enter the number ";     cin >> num;     i =2 ;     while(1){        if (num%i==0) {        if(num == i){            cout << "Prime Number";             break;         } else {cout << "Not Prime"; break; } } else {        i++; } } }```

 shabbir 27Nov2008 18:21

Re: Check if a number is prime or not

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

 back from retirement 30Nov2008 22:16

Re: Check if a number is prime or not

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

 skp819 19Dec2008 13:23

Re: Check if a number is prime or not

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:";         }     } }```

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