The Test Write a program, TestForPrimes, that reads a file of whole numbers and

Question

The Test
Write a program, TestForPrimes, that reads a file of whole numbers and writes only the prime numbers to a second file. Write you name as comment at the beginning of the program

A prime number is a positive integer that has two distinct divisors – 1 and itself. By this definition 1 is not a prime number.

How do recognize prime numbers?

Write a function isPrime that returns true if its parameter is a prime number and false if it is not a prime number.

An algorithm for the function is

number = abs(number)
if number = 0 then return false
else if number = 1 then return false
else if number modulo 2 is 0 then return false
else
factor = 3
remainder = number modulo factor
upper bound = floor(square_root(number))
while factor <= upper bound and remainder ? 0
factor = factor + 2
remainder = number modulo factor
end while
if factor > upper bound then
return true
else
return false
end if
end if

Note “modulo” is the C++ modulus operator “%”
There is a C++ floor function, a C++ sqrt function, and a C++ abs function
You have to include cmath to use these functions

Explanation / Answer

please rate - thanks //Name
#include <iostream>
#include <fstream>
#include <cmath>
using namespace std;
bool isPrime(int);
int main()
{
char filename[80];
int num;
ifstream in;
ofstream out;
cout<<"Enter name of input file: ";
cin>>filename;
in.open(filename);      
if(in.fail())          
   { cout<<"input file did not open please check it ";
   system("pause");
   return 1;
   }
cout<<"Enter name of output file: ";
cin>>filename;
out.open(filename);   
in>>num;
while(in)
{if(isPrime(num))
      out<<num<<endl;
   in>>num;
   }
  
out.close();
in.close();
return 0;
}
bool isPrime(int n)
{int i;
if(n<0)
   n=-n;
if(n<=1)
   return false;
for(i=2;i<=floor(sqrt(n));i++)
   if(n%i==0)               //if you find a factor the number isn't prime
      return false;
return true;                // get here only if no factors
}

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