/*
   testfunc17.cpp
   CIS 150
   2008-06-10
   David Klick
   
   Recursive and iterative greatest common divisor implementations.
*/

#include <iostream>
#include <cstring>
#include <climits>
using std::cin;
using std::cout;

int gcd_r(int a, int b);  // recursive gcd function
int gcd_i(int a, int b);  // iterative gcd function
int getInt(char* prompt, int min, int max);
char getChoice(char* prompt, char* allowed);
void cont();

int main(int argc, char* argv[]) {
    char ans;     // holds user answer for "run again?"
    int n1, n2, result;
   
    cout << "GCD calculator\n";
    do {
        // get numbers from user for GCD calc
        n1 = getInt("Enter an integer greater than 0: ", 1, INT_MAX);
        n2 = getInt("Enter another integer greater than 0: ", 1, INT_MAX);
      
        // calculate and display recursive GCD
        result = gcd_r(n1, n2);
        cout << "The GCD of " << n1 << " and " << n2 << " is "
             << result << " (recursive)\n";

        // calculate and display non-recursive GCD
        result = gcd_i(n1, n2);
        cout << "The GCD of " << n1 << " and " << n2 << " is "
             << result << " (non-recursive)\n";
      
        // find out if user wants to run gcd again
        ans = getChoice("Would you like to calculate another GCD? (Y/N) ", "YyNn");
    } while (ans == 'Y');

    // say "Goodnight" Gracie
    cout << "Normal program termination.\n";
    cont();
    
    return 0;
}

/*
    int getInt(char* prompt, int min, int max);
   
    Arguments:
        prompt: a pointer to a C-style string to be used as a prompt
        min: the minimum value allowed to be entered
        max: the maximum value allowed to be entered
   
    Returns: an integer entered by the user
   
    Prompts user with message passed in as argument and returns
    the integer value entered. The number must be between min and
    max (inclusive) or the user will be reprompted to enter
    another number. Note: For simplicity, no error checking on
    input is done, therefore this function may crash the program
    on invalid input.
*/
int getInt(char* prompt, int min, int max) {
    int num;
    do {
        cout << prompt;
        cin >> num;
        if (num < min) cout << "Error: value below minimum allowed\n";
        else if (num > max) cout << "Error: value above maximum allowed\n";
    } while (num<min || num>max);
    return num;
}

/*
    char getChoice(char* prompt, char* allowed);
   
    Arguments:
        char* prompt: a C-style string containing the prompt to show the user
        char* allowed: a C-style string containing all allowed user responses
            (each valid response being a single character)
   
    Returns: the user's choice (a character)
   
    Displays a prompt and then waits for the user to
    enter an allowed choice (a single character). Once
    a valid choice has been made, the function returns
    it to the calling function.
*/
char getChoice(char* prompt, char* allowed) {
    char ans;
    do {
        cout << prompt;
        cin >> ans;
        ans = toupper(ans);  // convert answer to upper case
        if (strchr(allowed, ans) == NULL) cout << "Error: Invalid choice\n";
    } while (strchr(allowed, ans) == NULL);
    return ans;
}

/*
    int gcd_r(int a, int b);
   
    Arguments:
        int a: an arbitrary integer value
        int b: an arbitrary integer value
   
    Returns: the greatest common divisor of a and b

    Calculates and returns the greatest common divisor
    of two integers using a recursive algorithm.
*/
int gcd_r(int a, int b) {
    if (a%b == 0) return b;
    else return gcd_r(b, a%b);
}

/*
    int gcd_i(int a, int b);
   
    Arguments:
        int a: an arbitrary integer value
        int b: an arbitrary integer value
   
    Returns: the greatest common divisor of a and b

    Calculates and returns the greatest common divisor
    of two integers using a non-recursive (and quite
    inefficient) algorithm.
*/
int gcd_i(int a, int b) {
   int i = a<b ? a : b;  // set i to minimum value
   while (i >= 2) {
      if (a%i==0 && b%i==0) return i;
      else i--;
   }
   return i;
}

/*
    void cont();
   
    Arguments: none
   
    Returns: nothing
   
    Clears input buffer and pauses waiting for user 
    to press Enter.
*/
void cont() {
    if (cin.rdbuf()->sungetc() != -1 && cin.get() != '\n') cin.ignore(80,'\n');
    cout << "Press enter to continue...";
    cin.get();
}