Use of loop, l earn to organize code within a function, Learn to pass data to an

Question

Use of loop, learn to organize code within a function, Learn to pass data to and return Boolean data from function

Write a function name isPrime, which takes an integer as an argument and returns true if the argument is a prime number, or false otherwise. Demonstrate the function in a complete program that reads in an integer that is less than 3001 stores a list of all the prime numbers from 2 through that number in a file named "PrimeList.txt" and to the standard output.Title, Prompts, Output, Labels:

Program will write output to the file and to the standard output.

After closing the file, the program writes to the standard output:

a. on a line by itself :

b. a list of primes

Prime numbers are written to PrimeList.txt

Input Validation If the value read in exceeds 3000, the program writes on a line

by itself in standard output:

Your input integer should be less than 3001. Try again.

Explanation / Answer

Below are the two program written in C++ to achive the requested task:

#include <iostream>
using namespace std;

bool isPrime (int num);   
int main ()
{
int num=0;

cout << "Enter a number to check if it is prime: "; //Enter a number to check whether it's prime or not   
cin >> num;

if (isPrime(num)==true)
cout << num << " is prime.";
else
cout << num << " is NOT prime.";

return 0;
}
bool isPrime(int input)
{
if(input<1)
return false;
else if (input == 1||input ==2 ||input==3)
{
return true;
}
else
{
for(int i=2; i<input; i++)
{
if(input%i==0)
return false;
}
return true;
}
}

#include <iostream>
#include <fstream>
using namespace std;

bool isPrime(int);

int main()
{
int num=0;
int i;
bool prime;

ofstream outFile;
outFile.open("PrimeList.txt"); //Prime No.s will be written to PrimeList.txt

while (num == 0 )
{
cin >> num;
}

for(i=2;i<num;i++)
if(isPrime(i))
outFile << i << " ";

cout << "Prime numbers written to PrimeList.txt. ";
outFile.close();
return 0;
}
bool isPrime(int n)
{
int i;
for(i=2;i<n-1;i++)
if(n%i==0)
return false;
return true;
}

Please comment if you face any issue in understanding anything on this C++ code. Happy to help :)

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