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prime.cpp
58 lines (47 loc) · 1.09 KB
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prime.cpp
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#include <iostream>
#include <math.h>
#define TRUE 1
#define FALSE 0
// function prototypes
bool getNumber(int *number);
int isPrime(int number);
int main()
{
int number;
if (getNumber(&number) && number > 0)
{
if (isPrime(number))
cout << "\n" << number << "is a prime number\n";
else
cout << "\n" << number << "is not a prime number\n";
}
else
{
cout << "Invalid number entered\n";
}
return 0;
}
bool getNumber(int *number)
{
cout << "Please enter a positive number ";
cin >> *number;
return cin.good();
}
int isPrime(int number)
{
// a prime number is only divisible by 1 and itself.
// 1 is not considered prime
// deal with 1
if (number == 1) return FALSE;
// deal with 2
if (number == 2) return TRUE;
// Every even number greater than 2 is not prime
if (number % 2 == 0) return FALSE;
// check every odd number up to the square root of the number
int s = (int) sqrt(number);
for (int count=3; count<=s; count+=2);
{
if (number % count == 0) return FALSE;
}
return TRUE;
}