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2D Array Manipulation Guide

This document contains code snippets for performing various operations on 2D arrays in C, including: 1) Reversing the order of elements in a 2D array by swapping elements between the first and last rows. 2) Transposing a matrix by swapping elements between rows and columns. 3) Rotating all elements of a 2D array by shifting each element to the left or up one space. 4) Setting the elements of the outer rows and columns of an array to zero while leaving inner elements unchanged. 5) Counting the number of duplicate values in a 2D array by copying elements to a 1D array, sorting, and scanning for duplicates.

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Keshav IS
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99 views3 pages

2D Array Manipulation Guide

This document contains code snippets for performing various operations on 2D arrays in C, including: 1) Reversing the order of elements in a 2D array by swapping elements between the first and last rows. 2) Transposing a matrix by swapping elements between rows and columns. 3) Rotating all elements of a 2D array by shifting each element to the left or up one space. 4) Setting the elements of the outer rows and columns of an array to zero while leaving inner elements unchanged. 5) Counting the number of duplicate values in a 2D array by copying elements to a 1D array, sorting, and scanning for duplicates.

Uploaded by

Keshav IS
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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reverse the order of the elements in a 2D array

#include <stdio.h>
#include <stdlib.h>
#define NUMCOLS 4
#define NUMROWS 8
/* Puzzle D11 -- reverse the order of the elements in a 2D array */
int reverse2D( int x[][NUMCOLS], int nrows )
{
int r, c;
int temp;
/* Swap elements in the full rows of the first half of */
/* the array with elements in full rows of the last half */
for ( r=0; r<nrows/2; r++ )
for ( c=0; c<NUMCOLS; c++ )
{
temp = x[r][c];
x[r][c] = x[nrows-1-r][NUMCOLS-1-c];
x[nrows-1-r][NUMCOLS-1-c] = temp;
}
/* If there are an odd number of rows, deal with the middle row */
if ( nrows%2 == 1 )
{
r = nrows/2;
for ( c=0; c<NUMCOLS/2; c++ )
{
temp = x[r][c];
x[r][c] = x[nrows-1-r][NUMCOLS-1-c];
x[nrows-1-r][NUMCOLS-1-c] = temp;
}
}

Transpose a matrix
#define NUMCOLS 5
int transpose( int x[NUMCOLS][NUMCOLS] )
{
int r, c, temp ;

for ( r=0; r<NUMCOLS; r++ )


for ( c=0; c<r; c++ )
{
temp
= x[r][c];
x[r][c] = x[c][r];
x[c][r] = temp;
}

Rotate the elements of a 2D array


void rotate2D ( int x[][NUMCOLS], int nrows )
{
int r, c, elmnt00;
elmnt00 = x[0][0];
for ( r=0; r<nrows; r++ )
for ( c=0; c<NUMCOLS; c++ )
if
( c>=1 ) x[r][c-1] = x[r][c];
else if ( r>=1 ) x[r-1][NUMCOLS-1] = x[r][c];
x[nrows-1][NUMCOLS-1] = elmnt00 ;
}

Zero the edges of an Array


/* Puzzle D16 -- Zero the edges of an Array
|
| Change the elements of the outer rows and
| columns of an array to zero. Leave all other
| elements unaffected.
|
*/
int zeroEdges ( int x[][NUMCOLS], int nrows )
{
int j;
/* row 0 */
for ( j=0; j<NUMCOLS; j++ ) x[0][j] = 0;
/* row nrows-1 */
for ( j=0; j<NUMCOLS; j++ ) x[nrows-1][j] = 0;
/* column 0 */
for ( j=0; j<nrows; j++ ) x[j][0] = 0;
/* column NumColumns-1 */
for ( j=0; j<nrows; j++ ) x[j][NUMCOLS-1] = 0;

Count the number of duplicate values in a 2D array of ints


int numberDuplicates( int x[][NUMCOLS], int nrows )
{
int r, c;
/* indexes to the current array element */
int j;
/* index into array[] */
int array[nrows*NUMCOLS];
int duplicateCount = 0;
int inRun = 0;
/* Copy elements from x[][] to array[] */
j = 0;
for ( r=0; r<nrows; r++ )

for ( c=0; c<NUMCOLS; c++ )


array[ j++ ] = x[r][c];
/* Sort the 1D array */
selectionSort( array, nrows*NUMCOLS );

/* Scan the 1D array for duplicates */


for ( j=0; j<nrows*NUMCOLS-1; j++ )
{
if ( !inRun && array[j] == array[j+1] )
{
inRun = 1;
duplicateCount += 2 ;
}
else if ( inRun && array[j] == array[j+1] )
duplicateCount++ ;
else
inRun = 0;
}
return duplicateCount;

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