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Comparing arrays

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coolmel55

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Comparing arrays

Oct 4th, 2004

How do I compare what is in one array with what is in another array?

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Re: Comparing arrays

Oct 4th, 2004

Loop through all array elements and compare each element; if all elements are the same, consider the arrays equal. Or use memcmp, which essentially does this.

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Narue

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Re: Comparing arrays

Oct 4th, 2004

>Or use memcmp, which essentially does this.
memcmp uses a shallow byte-by-byte comparison, so depending on the type of items in the array this might not be a good idea.

I'm here to prove you wrong.

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Re: Comparing arrays

Oct 4th, 2004

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Originally Posted by Narue

>Or use memcmp, which essentially does this.
memcmp uses a shallow byte-by-byte comparison, so depending on the type of items in the array this might not be a good idea.

I know what you are saying, but would you mind listing examples.

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djextazy

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Re: Comparing arrays

Oct 5th, 2004

It'll be something like this:

#include <iostream.h>
#include <conio.h>
void main()
{ clrscr(); int a[50],b[50],i,n,g;
cout<<"Give the number of elements of both vectors: "; cin>>n;
for(i=1;i<=n;i++) { cout<<"a["<<i<<"]= "; cin>>a[i]; } /* give the elements of the first vector */
for(i=1;i<=n;i++) { cout<<"b["<<i<<"]= "; cin>>b[i]; } /* give the elements of the second vector */
g=1; // we presume that the vectors are equal
while(g==1)
{ g=0;
for(i=1;i<=n;i++) if(a[i]==b[i]) g=1; } /* if the number of the component is the same (i) and the value of the component is the same , then g=1 and the while { } repeats until it ends or finds unequal components */
if(g==1) cout<<"The arrays are equal!";
else cout<<"The arrays aren't equal!";
getch();
}

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lara_

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Re: Comparing arrays

Oct 5th, 2004

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Originally Posted by djextazy

It'll be something like this:

#include <iostream.h>
#include <conio.h>
void main()
{ clrscr(); int a[50],b[50],i,n,g;
cout<<"Give the number of elements of both vectors: "; cin>>n;
for(i=1;i<=n;i++) { cout<<"a["<<i<<"]= "; cin>>a[i]; } /* give the elements of the first vector */
for(i=1;i<=n;i++) { cout<<"b["<<i<<"]= "; cin>>b[i]; } /* give the elements of the second vector */
g=1; // we presume that the vectors are equal
while(g==1)
{ g=0;
for(i=1;i<=n;i++) if(a[i]==b[i]) g=1; } /* if the number of the component is the same (i) and the value of the component is the same , then g=1 and the while { } repeats until it ends or finds unequal components */
if(g==1) cout<<"The arrays are equal!";
else cout<<"The arrays aren't equal!";
getch();
}

have you test running your program?

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Narue

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Re: Comparing arrays

Oct 5th, 2004

>I know what you are saying, but would you mind listing examples.
The simplest example is an array of pointers. Do you want to compare the value of the pointers or the value of the addresses pointed to:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <stdio.h>
#include <string.h>
 
int main ( void )
{
  static int a = 10;
  static int b = 20;
  static int c = 10;
  static int d = 20;
  int *aa[2] = { &a, &b };
  int *ab[2] = { &c, &d };
 
  if ( memcmp ( aa, ab, 2 * sizeof ( int ) ) == 0 )
    puts ( "Equal" );
  else
    puts ( "Not equal" );
 
  return 0;
}
#include <stdio.h>
#include <string.h>

int main ( void )
{
  static int a = 10;
  static int b = 20;
  static int c = 10;
  static int d = 20;
  int *aa[2] = { &a, &b };
  int *ab[2] = { &c, &d };

  if ( memcmp ( aa, ab, 2 * sizeof ( int ) ) == 0 )
    puts ( "Equal" );
  else
    puts ( "Not equal" );

  return 0;
}

Most likely it's the former, so memcmp would give the wrong answer unless by some coincidence both arrays all have pointers that reference the same addresses.

>It'll be something like this
No it wouldn't, that code is awful. The concept is sound, but the implementation sucks. Here are a few reasons why:

>#include <iostream.h>
Not C++.

>#include <conio.h>
No portable.

>void main()
Undefined.

>clrscr();
VERY nonportable.

>cin>>n;
Not robust.

>for(i=1;i<=n;i++)
Poor style, not idiomatic.

>cin>>a[i];
Not robust, difficult to recover from on error.

>g=1;
>while(g==1)
>{ g=0;
Confused and awkward.

>getch();
Not portable and stupid because there's a standard alternative that works just as well.

And on top of that, you didn't use code tags...

I'm here to prove you wrong.

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lara_

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Re: Comparing arrays

Oct 5th, 2004

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream.h>
 
void main()
{	int a[50],b[50],i,n,g;
 
	cout<<"Give the number of elements of both vectors: "; cin>>n;
 
	for(i=1;i<=n;i++) { cout<<"a["<<i<<"]= "; cin>>a[i]; } 
 
	for(i=1;i<=n;i++) { cout<<"b["<<i<<"]= "; cin>>b[i]; } 
 
	g=1;
 
	while(g==1)
	{			
		for(i=1;i<=n;i++) 
 
			if(a[i]==b[i]) 
				g=1;
 
			else {
				g=0;
				break;
			}
 
 
		if(g==0)
			break;
		g++;
	}  
 
	if(g==0)
		cout<<"The arrays aren't equal!";
 
	else 
		cout<<"The arrays are equal!";
}
#include <iostream.h>

void main()
{	int a[50],b[50],i,n,g;
	
	cout<<"Give the number of elements of both vectors: "; cin>>n;
		
	for(i=1;i<=n;i++) { cout<<"a["<<i<<"]= "; cin>>a[i]; } 
	
	for(i=1;i<=n;i++) { cout<<"b["<<i<<"]= "; cin>>b[i]; } 

	g=1;
	
	while(g==1)
	{			
		for(i=1;i<=n;i++) 
			
			if(a[i]==b[i]) 
				g=1;
			
			else {
				g=0;
				break;
			}
		

		if(g==0)
			break;
		g++;
	}  
		
	if(g==0)
		cout<<"The arrays aren't equal!";
	
	else 
		cout<<"The arrays are equal!";
}

i just learn c++ programming. so i only can get this...

i never use memcmp before, thanks for the example you gave...!

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Narue

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Re: Comparing arrays

Oct 5th, 2004

>i just learn c++ programming. so i only can get this...
Then don't accept poor code. Try this for the comparison instead:

 Help with Code Tags 
 C++ Syntax (Toggle Plain Text) 
#include <iostream>
 
bool is_equal ( int a[], int b[], int size )
{
  for ( int i = 0; i < size; i++ ) {
    if ( a[i] != b[i] )
      return false;
  }
 
  return true;
}
 
int main()
{
  int a[] = {1,2,3,4,5,6,7,8,9};
  int b[] = {1,2,3,4,5,6,7,8,9};
 
  if ( is_equal ( a, b, 9 ) )
    std::cout<<"They're equal"<<std::endl;
  else
    std::cout<<"They're not equal"<<std::endl;
}
#include <iostream>

bool is_equal ( int a[], int b[], int size )
{
  for ( int i = 0; i < size; i++ ) {
    if ( a[i] != b[i] )
      return false;
  }

  return true;
}

int main()
{
  int a[] = {1,2,3,4,5,6,7,8,9};
  int b[] = {1,2,3,4,5,6,7,8,9};

  if ( is_equal ( a, b, 9 ) )
    std::cout<<"They're equal"<<std::endl;
  else
    std::cout<<"They're not equal"<<std::endl;
}

I'm here to prove you wrong.

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djextazy

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Re: Comparing arrays

#10

Oct 5th, 2004

•

Originally Posted by lara_

have you test running your program?

I apologize. That one I didn't test. Here is the correct version , tested :cheesy: :

#include <iostream>
#include <conio.h>
using namespace std;
int main()
{ int a[50],b[50],i,j,n;
cout<<"Give the number of elements of both vectors: "; cin>>n;
for(i=1;i<=n;i++) { cout<<"a["<<i<<"]= "; cin>>a[i]; }
for(i=1;i<=n;i++) { cout<<"b["<<i<<"]= "; cin>>b[i]; }
i=0;
while(i<n) for(j=1;j<=n;j++) if(a[j]==b[j]) i++;
if(i==n) cout<<"The arrays are equal!";
else cout<<"The arrays aren't equal!";
getch();
}