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Recursive program issue

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Join Date: Nov 2008

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nedsnurb

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Recursive program issue

Nov 19th, 2008

Hi
Have written this code for a program that requires the user to either enter 1 or 2 dependant on whether the program solves the problem of finding the divisors of any given to numbers by recursive or iteration methods.

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 C++ Syntax (Toggle Plain Text) 
 
#include<iostream>
 
using namespace std; 
 
int recursiveGCD(int ,int );   
int iterativeGCD(int ,int );
int input;
 
void main()
 
{
   int x,y;
   cout<<"Please enter the two numbers : ";
   cin>>x>>y;
   cout<<"Enter 1 for recursive calculation, 2 for iterative";
   cin>>input;
   { 
	if input == 1
	return recursiveGCD;
	if input == 2
	return iterativeGCD;
   }
   cout<<"The Greatest Common Divisor of ("<<x<<","<<y<<") = " << recursiveGCD(x,y)<<endl;
}
 
 
int recursiveGCD(int x,int y)
{
   if(y>x)return recursiveGCD(y,x);
   if(x==y)return x;
   if(x%y==0)return y;
   return recursiveGCD(x,x-y);
 
}
 
int iterativeGCD(int x,int y)
{	
	if (y == 0)
		return x;
	else 
		return iterativeGCD(y, x % y);
}
#include<iostream>

using namespace std; 

int recursiveGCD(int ,int );   
int iterativeGCD(int ,int );
int input;

void main()

{
   int x,y;
   cout<<"Please enter the two numbers : ";
   cin>>x>>y;
   cout<<"Enter 1 for recursive calculation, 2 for iterative";
   cin>>input;
   { 
	if input == 1
	return recursiveGCD;
	if input == 2
	return iterativeGCD;
   }
   cout<<"The Greatest Common Divisor of ("<<x<<","<<y<<") = " << recursiveGCD(x,y)<<endl;
}


int recursiveGCD(int x,int y)
{
   if(y>x)return recursiveGCD(y,x);
   if(x==y)return x;
   if(x%y==0)return y;
   return recursiveGCD(x,x-y);

}

int iterativeGCD(int x,int y)
{	
	if (y == 0)
		return x;
	else 
		return iterativeGCD(y, x % y);
}

However I am getting the error C2061, saying that input is undeclared when I seem to have to declared it at the top??

Many Thanks

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Join Date: Nov 2008

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Reputation: Lokolo is an unknown quantity at this point

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Lokolo

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Re: Recursive program issue

Nov 19th, 2008

Why don't you just declare it in main? (like you have with x and y)

Last edited by Lokolo; Nov 19th, 2008 at 12:06 pm.

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chococrack chococrack is offline

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Re: Recursive program issue

Nov 19th, 2008

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int recursiveGCD(int ,int );   
int iterativeGCD(int ,int );
int input;
int recursiveGCD(int ,int );   
int iterativeGCD(int ,int );
int input;

The first two are fine (function prototypes).

However the last line
int input;
when I was first reading I was thinking perhaps it was meant to be a function. If that was the original intention, then you would have needed the necessary parenthesis to have it appear as a function

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int input();
int input();

HOWEVER, the way you're using it you want to go with what Lokolo said in the above post, declare input in your main function

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
int main
{
    int input;
...
}
int main
{
    int input;
...
}

I would love to change the world, but they won't give me the source code

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Join Date: Nov 2008

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nedsnurb

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Re: Recursive program issue

Nov 19th, 2008

hi guys thanks for the quick replies however I did try this and it still throws up the error even when it is changed?

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include<iostream>
 
using namespace std; 
 
int recursiveGCD(int ,int );   
int iterativeGCD(int ,int );
 
int main()
{
   int input;
   int x,y;
   cout<<"Please enter the two numbers : ";
   cin>>x>>y;
   cout<<"Enter 1 for recursive calculation, 2 for iterative";
   cin>>input;
 
   { 
	if input == 1
	return recursiveGCD;
	if input == 2
	return iterativeGCD;
   }
 
   cout<<"The Greatest Common Divisor of ("<<x<<","<<y<<") = " << recursiveGCD(x,y)<<endl;
}
 
 
int recursiveGCD(int x,int y)
{
   if(y>x)return recursiveGCD(y,x);
   if(x==y)return x;
   if(x%y==0)return y;
   return recursiveGCD(x,x-y);
 
}
 
int iterativeGCD(int x,int y)
{	
	if (y == 0)
		return x;
	else 
		return iterativeGCD(y, x % y);
}
#include<iostream>

using namespace std; 

int recursiveGCD(int ,int );   
int iterativeGCD(int ,int );

int main()
{
   int input;
   int x,y;
   cout<<"Please enter the two numbers : ";
   cin>>x>>y;
   cout<<"Enter 1 for recursive calculation, 2 for iterative";
   cin>>input;
  
   { 
	if input == 1
	return recursiveGCD;
	if input == 2
	return iterativeGCD;
   }
   
   cout<<"The Greatest Common Divisor of ("<<x<<","<<y<<") = " << recursiveGCD(x,y)<<endl;
}


int recursiveGCD(int x,int y)
{
   if(y>x)return recursiveGCD(y,x);
   if(x==y)return x;
   if(x%y==0)return y;
   return recursiveGCD(x,x-y);

}

int iterativeGCD(int x,int y)
{	
	if (y == 0)
		return x;
	else 
		return iterativeGCD(y, x % y);
}

Last edited by nedsnurb; Nov 19th, 2008 at 12:30 pm.

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Join Date: Nov 2008

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Lokolo

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Re: Recursive program issue

Nov 19th, 2008

1. Next time try to tell us which line it is.

2. If( ) has brackets.

i.e.

if input == 1
return recursiveGCD;
if input == 2
return iterativeGCD;

Should be

if (input == 1)
return recursiveGCD;
if (input == 2)
return iterativeGCD;

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mrboolf

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Re: Recursive program issue

Nov 19th, 2008

That's not where the problem lies.

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
{ 
	if input == 1
	return recursiveGCD;
	if input == 2
	return iterativeGCD;
   }
{ 
	if input == 1
	return recursiveGCD;
	if input == 2
	return iterativeGCD;
   }

is wrong both from the syntax point of view and logically. You miss some parentheses and you try to call iterativeGCD and recursiveGCD (that are functions) without passing them their arguments (x and y in this case). You should call a function like this recursiveGCD(x, y) . Then I think you don't want to return their output: in fact you try to print it with cout just in the following line. You should store their returned value in a variable and then print that value or directly put the cout instruction inside the if.

Just another thing: both your function are recursive, even the one named iterativeGCD.

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nedsnurb

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Re: Recursive program issue

Nov 19th, 2008

thanks for your help, think i'll go back to the drawing board really! cheers

Last edited by nedsnurb; Nov 19th, 2008 at 12:46 pm.

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chococrack chococrack is offline

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Re: Recursive program issue

Nov 19th, 2008

A common main function appears as

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int main()
{
    // code
    return 0;
}
int main()
{
    // code
    return 0;
}

Yours appears like this:

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 C++ Syntax (Toggle Plain Text) 
int main()
{
// little bit of code
    { // unecessary brackets
        if(some contidion)
            return Function1; // trying to return a value
        else
            return Function2; // trying to return a value
    } // more unessary brackets
// more code
}  // oops no return 0
int main()
{
// little bit of code
    { // unecessary brackets
        if(some contidion)
            return Function1; // trying to return a value
        else
            return Function2; // trying to return a value
    } // more unessary brackets
// more code
}  // oops no return 0

You need to take out the brackets and give the functions something to store the values in (and pass their parameters.

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int main()
{
    int getRecurs, getItera;
// ...
    if (input==1)
        getRecurs = recursiveGCD(PUT PARAMETERS!!!);
 
    if (input == 2)
        getItera = iterativeGCD(PARAMETERS);
// ....
return 0;
}
int main()
{
    int getRecurs, getItera;
// ...
    if (input==1)
        getRecurs = recursiveGCD(PUT PARAMETERS!!!);
    
    if (input == 2)
        getItera = iterativeGCD(PARAMETERS);
// ....
return 0;
}

I still love you, even if no one else does

Last edited by chococrack; Nov 19th, 2008 at 12:52 pm.

I would love to change the world, but they won't give me the source code

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Narue

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Re: Recursive program issue

Nov 19th, 2008

>// unecessary brackets
Which can be used to introduce a new scope without adding a one-off function or doing something dumb like:

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if ( true ) {
  // Stuff
}
if ( true ) {
  // Stuff
}

You'd see it more in C prior to C99 where you want to restrict the scope of a for loop control variable:

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/* i isn't visible here */
 
{
  int i;
 
  for ( i = 0; i < N; i++ ) {
    /* Do stuff */
  }
}
 
/* nor is i visible here. yay */
/* i isn't visible here */

{
  int i;

  for ( i = 0; i < N; i++ ) {
    /* Do stuff */
  }
}

/* nor is i visible here. yay */