Prime Number Program, How can I improve?

[Shinedevil]

#include <iostream>
using namespace std;
long int math;
long int check;
long int divider = 1;
long int inputnum;
void dividerp();
void counter();
void inputp();

void dividerp(){
     math = inputnum/divider;
     if (math == 1 or inputnum == 2 or inputnum == 1){
              cout<<"You do have a prime number there!"<<endl;
              system("PAUSE");
              system("CLS");
              math = 0;
              inputp();
              }
     else if (math == inputnum){
          counter();
          }
     else if ( inputnum % divider != 0 ){
          counter();
          }

     else if (math >= 1){
              cout<<"You do not have a prime number!"<<endl;
              system("PAUSE");
              system("CLS");
              math = 0;
              inputp();
              }
     else{
              counter();
              }
     }
     
void counter(){
     divider = divider + 1;
     dividerp();
     }
     
void inputp(){
     divider = 1;
     cout<< "Please type in a number."<<endl;
     cout<< "I will check to see if it is a prime number."<<endl;
     cin>> inputnum;
     if (inputnum >= 1){
               dividerp();
               }
     else {
          cout<<"Sorry you have not typed in an accurate number."<<endl;
          system("PAUSE");
          system("CLS");
          inputnum = 0;
          inputp();
     }
     }
     
int main(){
    cout<< "Hello and welcome to the program."<<endl;
    inputp();
}

I'm still learning, (Went back from allegrogl, totally forgot how to do this stuff) Is there a way to improve this code, or types of functions that can improve performance (Not like there is a problem with it). And how can I increase the number range that I can use to find more prime numbers? I can't use floats/doubles due to the fact that they for some reason do not like to have math applied to them, is there a way to fix that?

EDIT: Optimizing code, that's the word i'm looking for. How can I optimize code?

[NathanOliver]

you could use a simple for loop in your main function and do a brute force method like your functions do or you could use the Sieve of Eratosthenes method which works very well. http://en.wikipedia.org/wiki/Sieve_of_Eratosthenes

also on line 13 in your code you are using or which is incorrect in c++. || = or and && = and in c++

[Clinton Portis]

When testing for primes, you only need to test half the range:

bool is_prime = true;

cout << "Enter a numeral: ";
cin >> number;

if(number == 1 || number == 3)
{
     cout << "Number is prime.";
     exit(0);
}

for(int i=2; i<number/2; i++)
{
     //If there is any case of no remainder, then number is not prime
     if(number%i)
     {
          is_prime = false;
          break;
     }
}

if(is_prime)

     cout << number << " is a prime number. ";

else 

     cout << number << " is not a prime number. ";

There might be easier ways to do this.. this is just something I came up with off the top of me' head.

[Shinedevil]

also on line 13 in your code you are using or which is incorrect in c++. || = or and && = and in c++

I'm using Dv-C++ 4.9.9.2 writer and compiler and it said that "or" was ok when it was compiling, was just having a brain fart :P

[NathanOliver]

i bow before your compiler then ;). seriously i would use the standard operators since i doubt it would work on older compilers.

[Shinedevil]

Other than one post which could clean up my code, I have gotten no useful replies. I just want to improve my skill and learn new functions that might be helpful, for I have not any other means of doing so.

[Mahfuz_1]

You can see this post if you wish.
http://www.mahfuzsust.info/2013/10/10/prime-numbers-sieve-of-eratosthenes/