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# how to compare integers in an array

Posted on 2002-05-27
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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
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Question by:jurij

LVL 86

Accepted Solution

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.

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Expert Comment

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.
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