bohling

01-01-2012, 10:10 AM

Hi,

I have figured out the old tired prime number program that a lot of newbies like myself attempt to tackle when we hit the ground running with c++. What I am interested in is expanding it to something that not only displays the primes of a number, but the number of primes. To wit:

Please enter a number: 10

There are 4 primes in 10. Those primes are:

7 5 3 2

Do you wish to continue (y/n)?

I have all of that down except for the "there are x primes". I have tried count and if/else/do but I am getting hopelessly confused. Is there a simple or other way to do it?

Here is my code so far...

#include <iostream>

using namespace std;

int main()

{

int x; // input

int y; // divisor

int z; // prime

char key; // to continue or not

cout << "This program will allow you to enter a number and will display all and how many prime numbers from that number to 0." << endl << endl;

do

{

cout << "Please enter a number: ";

cin >> x;

cout << endl;

// cout << "There are " << counter << " primes in that range." << endl;

cout << "All primes in this range are:" << endl << endl;

for (z=x; z>=2; z--)

{

bool primeNo = false;

for (y=2; y<z; y++)

{

if (z % y == 0)

{

primeNo = true;

}

}

if (primeNo == false)

{

cout << z << " ";

}

}

cout << endl << endl;

cout << "Continue (y/n)? ";

cin >> key;

}

while (key == 'y'||key == 'Y');

cout << endl << endl;

system("PAUSE");

return 0;

}

I have figured out the old tired prime number program that a lot of newbies like myself attempt to tackle when we hit the ground running with c++. What I am interested in is expanding it to something that not only displays the primes of a number, but the number of primes. To wit:

Please enter a number: 10

There are 4 primes in 10. Those primes are:

7 5 3 2

Do you wish to continue (y/n)?

I have all of that down except for the "there are x primes". I have tried count and if/else/do but I am getting hopelessly confused. Is there a simple or other way to do it?

Here is my code so far...

#include <iostream>

using namespace std;

int main()

{

int x; // input

int y; // divisor

int z; // prime

char key; // to continue or not

cout << "This program will allow you to enter a number and will display all and how many prime numbers from that number to 0." << endl << endl;

do

{

cout << "Please enter a number: ";

cin >> x;

cout << endl;

// cout << "There are " << counter << " primes in that range." << endl;

cout << "All primes in this range are:" << endl << endl;

for (z=x; z>=2; z--)

{

bool primeNo = false;

for (y=2; y<z; y++)

{

if (z % y == 0)

{

primeNo = true;

}

}

if (primeNo == false)

{

cout << z << " ";

}

}

cout << endl << endl;

cout << "Continue (y/n)? ";

cin >> key;

}

while (key == 'y'||key == 'Y');

cout << endl << endl;

system("PAUSE");

return 0;

}