-bash-3.2$ gcc -o lemastsGCD lemastsGCD.cpp
/tmp/cca8g62Q.o: In function `__static_initialization_and_destruction_0(int, int)':
lemastsGCD.cpp:(.text+0x51): undefined reference to `std::ios_base::Init::Init()'
/tmp/cca8g62Q.o: In function `__tcf_0':
lemastsGCD.cpp:(.text+0x9a): undefined reference to `std::ios_base::Init::~Init()'
/tmp/cca8g62Q.o: In function `gcdr(int, int)':
lemastsGCD.cpp:(.text+0xb1): undefined reference to `std::cout'
lemastsGCD.cpp:(.text+0xb6): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
lemastsGCD.cpp:(.text+0xc7): undefined reference to `std::basic_ostream<char, std::char_traits<char> >::operator<<(int)'
lemastsGCD.cpp:(.text+0xd7): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
lemastsGCD.cpp:(.text+0xe8): undefined reference to `std::basic_ostream<char, std::char_traits<char> >::operator<<(int)'
lemastsGCD.cpp:(.text+0xf8): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::operator<< <std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&, char const*)'
lemastsGCD.cpp:(.text+0x100): undefined reference to `std::basic_ostream<char, std::char_traits<char> >& std::endl<char, std::char_traits<char> >(std::basic_ostream<char, std::char_traits<char> >&)'
lemastsGCD.cpp:(.text+0x108): undefined reference to `std::basic_ostream<char, std::char_traits<char> >::operator<<(std::basic_ostream<char, std::char_traits<char> >& (*)(std::basic_ostream<char, std::char_traits<char> >&))'
/tmp/cca8g62Q.o: In function `main':
lemastsGCD.cpp:(.text+0x166): undefined reference to `std::cout'
 

#include <iostream>
 
int gcdr(int a, int b);             // recursive function declaration
 
int gcdi(int a, int b);             // iterative function declaration
 
using namespace std;
 
int main(int argc, char *argv[])    // Command line arguments
{
 
 	if (argc != 4)                  // If the command line does not receive four
 	                                // arguments if statement is entered
	{
		cout << "\nProgram usage: program name.exe type of algorithm -r or -i integer integer\n";
									// Statement to user that an error has occur ed
		return -1;                  // Terminate program
	}
	int x,y,swap;                   // Variables to hold input integers from user
 	string GCDtype;                 // String variable to hold the type of function
 	                                // to be used.
 
	GCDtype = argv[1];              // Variable to save the type of function to be run
	swap = 0;                          // Integer variable used for swap
	x = atoi(argv[2]);              // Varable to hold first integer input
	y = atoi(argv[3]);              // Viable to hold second integer input
 
	if (x <= y)                     // If statement to swap integers in the case 
	                                // that the first integer is larger than second
	{
        swap = x;                   // set swap variable equal to x
        x = y;                      // set x equal to y
        y = swap;                   // set y equal to swap variable
	}
 
	if (GCDtype == "-r")            // If statement for recursive function
	{
		cout << "\nStarting recursion" << endl; // Inform user starting recursion
									// start of recursion
		cout << "gcd by recursive algorithm is " << gcdr(x, y)/* function call*/ << endl;
	}
	else if (GCDtype == "-i")       // Else if for iterative function
	{
									// Run GCDi function
		cout << "\ngcd by iterative algorithm is " << gcdi(x,y)/* function call*/ << endl;
	}
	else                            // Inform user that -r or -i was not entered
	{
		cout << "\nIncorrect use of program. Correct use is as follows\n";
		cout << "Program Name.exe -r or -i integer integer" << endl;
	}
    return -1;                      // End program
}
 
int gcdr(int a, int b)              // Function recursive
{
	cout << "Finding gcd(" << a << "," << b << ")" << endl;
    return ( b == 0 ? a : gcdr(b, a % b) ); // Run recursion until GCD is found
}
 
int gcdi(int a, int b)              // Function iterative
{
	int c;                          // Variable to hold b
 
  	while (b != 0)                  // Run while b does not equal zero
	{
    	c = b;
    	b = a % b;                  // b now equals a mod b
    	a = c;                      // a now equals what b was
  	}
  	return a;
}