First Unassisted Program

[jamonathin]

This is the first program I've written without the "assistance" of another. All it does is calculate the factors of a number. Although I do give my thanks to wtd and martin for their help with other crap such as the following . . .

c++:

#include <iostream> int num = 1, count = 1; int calculate () {     int store [num];             for (int i (1); i <= num; i++)     {         for (int q (1); q <= num; q++)         {             if (i * q == num)             {                   store [count] = q;                   count += 1;                   store [count] = i;                   count += 1;             }         }          }         std::cout << "The factors of " << num << " are:\n";     for (int w (1); w <= count/ 2; w+=2)     {         std::cout << "   " << store [w] << " x " << store [w+1] << "\n";     }         int wait;     std::cin >> wait;     return 0; } int main () {     std::cout << "Enter any number to find its factors.\n";     std::cin >> num;     std::cout << "\n   Please Wait . . .\n\n";             calculate (); }

[wtd]

My first thought:

Don't use global variables. If you need a piece of data to pass from one function to another, pass it an argument. Then simply calculate the factors, put them into a vector (or other data structure), and return that so the rest of the program can do what it will with that data.

c++:

#include <vector> std::vector<int> factors(int number) {    // ... }

[jamonathin]

I understand what you mean (your concept), I just don't know how I would call calculate now. I have . . .

c++:

std::vector<int> calculate (int numb)

But I don't know how to make calculate work, like this doesn't work.

c++:

calculate (num);

[wtd]

jamonathin wrote:

I understand what you mean (your concept), I just don't know how I would call calculate now. I have . . .

c++:

std::vector<int> calculate (int numb)

But I don't know how to make calculate work, like this doesn't work.

c++:

calculate (num);

If you implement it correctly it will work, but the thing to understand is that it won't be doing anything immediately apparent itself. Instead it'll be generating and returning a collection of ints which represent the factors of the input number.

You could then loop over them to output those numbers.

[wtd]

Take a look at this implementation, and if you have any questions, feel free to ask.

c++:

#include <iostream> #include <vector> bool is_prime(int number) {    for (int i(2); i <= number / i; ++i)    {       if (number % i == 0)       {          return false;       }    }    return true; } std::vector<int> factors(int number) {    std::vector<int> results;    while (!is_prime(number))    {       bool found(false);         for (int i(2); i <= number / i && !found; ++i)       {          if (number % i == 0)          {             results.push_back(i);             number /= i;             found = true;          }       }    }    results.push_back(number);    return results; } int main() {    int num;        std::cin >> num;    std::vector<int> f(factors(num));    for (std::vector<int>::iterator i(f.begin()); i != f.end(); i++)    {       std::cout << *i << std::endl;    }    return 0; }

[jamonathin]

I'm just going to say what I think the main things are (what I think they mean).

bool is_prime(int number) - Means its a boolean function that's an array (from a previous number and the array size can change with whatever int number is used with the function)

if (number % i == 0) - No idea. I tried the % in a different program, and I normally aways got 0 and the odd 1.

while (!is_prime(number)) - Nada clue

results.push_back(number); - Kinda get it, maybe a little explanation could help.

And lastly . .
for (std::vector<int>::iterator i(f.begin()); i != f.end(); i++)
- Not really sure how that works out Are you varing that vector then, and keep varing it, or are you just calling it for every i value. And not too sure what != means.

[wtd]

c++:

bool is_prime(int number)

Is a function which takes an int as an argument and returns true or false.

% is the modulo operator. It finds the remainder in integer division.

c++:

while (!is_prime(number))

Do the following while "number" is not prime.

We create an iterator, then advance it each time until it's at the end of the vector. != is "not equal".

[jamonathin]

Ohhh ok, sounds good man, all makes sense, thanks