Improve company productivity with a Business Account.Sign Up

x
?
Solved

how to compare integers in an array

Posted on 2002-05-27
2
Medium Priority
?
335 Views
Last Modified: 2010-04-02
Lets say I have 2 arrays:
----------------------------------------
int* a=new int[9]
int* b=new int[9]

a=[1,2,3,4,5,6,7,8,9]
b=[1,2,3,4,6,4,3,2,1]
----------------------------------------
compare(a,b,first_5) => false

Now.. how can I compare first 5 (or first n) integers, without having to use a while loop (or for)?
Is there a faster way at all (then to use a loop)?
Thank you!

Jurij
0
Comment
Question by:jurij
2 Comments
 
LVL 86

Accepted Solution

by:
jkr earned 800 total points
ID: 7037023
You can use 'memcmp()':

memcmp ( a, b, 5 * sizeof ( int));

This will do a binary compare for the first 5 elements in the arrays, which is equal to compare each of the elements.

Here's a smple from the VC++ docs

Example

/* MEMCMP.C: This program uses memcmp to compare
 * the strings named first and second. If the first
 * 19 bytes of the strings are equal, the program
 * considers the strings to be equal.
 */

#include <string.h>
#include <stdio.h>

void main( void )
{
   char first[]  = "12345678901234567890";
   char second[] = "12345678901234567891";
   int result;

   printf( "Compare '%.19s' to '%.19s':\n", first, second );
   result = memcmp( first, second, 19 );
   if( result < 0 )
      printf( "First is less than second.\n" );
   else if( result == 0 )
      printf( "First is equal to second.\n" );
   else if( result > 0 )
      printf( "First is greater than second.\n" );
   printf( "Compare '%.20s' to '%.20s':\n", first, second );
   result = memcmp( first, second, 20 );
   if( result < 0 )
      printf( "First is less than second.\n" );
   else if( result == 0 )
      printf( "First is equal to second.\n" );
   else if( result > 0 )
      printf( "First is greater than second.\n" );
}


Output

Compare '1234567890123456789' to '1234567890123456789':
First is equal to second.
Compare '12345678901234567890' to '12345678901234567891':
First is less than second.

0
 

Expert Comment

by:GregToombs
ID: 7037836
I think the suggested call to memcmp is the fastest route, simply because it has been optimized by previous programmers. Conceptually speaking, keep in mind that any such comparison, including memcmp itself, needs to use a loop of some description.
0

Featured Post

The 14th Annual Expert Award Winners

The results are in! Meet the top members of our 2017 Expert Awards. Congratulations to all who qualified!

Question has a verified solution.

Are you are experiencing a similar issue? Get a personalized answer when you ask a related question.

Have a better answer? Share it in a comment.

Join & Write a Comment

Unlike C#, C++ doesn't have native support for sealing classes (so they cannot be sub-classed). At the cost of a virtual base class pointer it is possible to implement a pseudo sealing mechanism The trick is to virtually inherit from a base class…
Article by: SunnyDark
This article's goal is to present you with an easy to use XML wrapper for C++ and also present some interesting techniques that you might use with MS C++. The reason I built this class is to ease the pain of using XML files with C++, since there is…
The goal of the video will be to teach the user the concept of local variables and scope. An example of a locally defined variable will be given as well as an explanation of what scope is in C++. The local variable and concept of scope will be relat…
The viewer will learn how to clear a vector as well as how to detect empty vectors in C++.

585 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question