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-   -   Swap two variables using macro (http://www.go4expert.com/articles/swap-variables-using-macro-t1732/)

 Ziaur Rahman 26Oct2006 18:42

Swap two variables using macro

The code to swap two variables using macro expansions

Code: C

`#include<stdio.h>#include<conio.h>#define SWAPE(x,y) int t;t=x;x=y;y=t;main(){    int a,b;        printf("\n Enter two number");    scanf("%d%d",&a,&b);    printf("\n Before swaping the Value of a=%d and b=%d",a,b);    SWAPE(a,b);    printf("\n After swap value of a=%d and b=%d",a,b);    return 0;}`

 nicenaidu 2Nov2006 13:35

Swap two numbers without using temp variable

//Code for swapping two numbers without using temp variable
Code: CPP

`#include <iostream>using namespace std;int main (){  int a = 10;  int b = 5;  cout << "before swap: a = " << a << " b = " << b << endl;    //Swapping numbers without using a temp var : method1  a = a ^ b;  b = b ^ a;  a = a ^ b;  cout << "after swap using method1: a = " << a << " b = " << b << endl;  //Swapping numbers without using a temp var : method2  a = a + b;  b = a - b;  a = a - b;  cout << "after swap using method2: a = " << a << " b = " << b << endl;  return 0;}`

 aurnk 22Dec2006 14:42

Re: Swap two variables using macro

better method is
usage of
#define swap(a,b) a^=b^=a^=b;

 aurnk 22Dec2006 14:43

Re: Swap two variables using macro

better method is
usage of
#define swap(a,b) a^=b^=a^=b;

one line swap without using temporary variable.

 Peter_APIIT 12Apr2007 11:15

Re: Swap two variables using macro

Hello nicenaidu, i have compiler the file you post in MS VS 2005 but the IDE complaint that cstiod.h error .

Your help is greatly appreciated by me and others.

 Vikrant Singh 24May2007 15:43

Re: Swap two variables using macro

Here is a suggestion...

Using ^ operator is not the best way of swapping two values.
Just consider is soemone try to SWAP same variable, like SWAP(A,A) what will happen?
A^A will clear the all of the bits of A, because of which A will lost its original value on calling SWAP macro.

Further swapping value using equation like A+B is not advisable , if A and B are very large values than result of this addition may cross the maximum value which an integer can store. We may end up with a incorrect result.

So we should not try to play smart with fancy instruction as far as swapping is concerned.

 oleber 25May2007 13:30

Re: Swap two variables using macro

Lets speak of C/C++

Why use a Macro and fix a type?

Template functions can do the work cleaner.

Code: CPP

`template <class TYPE>void swamp(TYPE &var1, TYPE &var2) {    TYPE var_temp = var1;    var1 = var2;    var2 = var_temp;}`

 Vikrant Singh 25May2007 18:59

Re: Swap two variables using macro

This can be done in Macro also…
Try this…
#define SWAP (A, B) struct tempStruct { char C[sizeof(A)];} swap_tmp;\
swap_tmp = *( struct tempStruct*) &A;\
*( struct tempStruct*) &A = *( struct tempStruct*) &B;\
*( struct tempStruct*) &B = swap_tmp;

 oleber 25May2007 20:04

Re: Swap two variables using macro

Correct to :p

Code:

```    #define SWAP(A, B) {struct tempStruct { char C[sizeof(A)];} swap_tmp;\     swap_tmp = *( struct tempStruct*) &A;\     *( struct tempStruct*) &A = *( struct tempStruct*) &B;\     *( struct tempStruct*) &B = swap_tmp;}```
Other wise you get problems when using diferent types

Code: CPP

`#include <cstdio>    #include <iostream>        using namespace std;        #define SWAP(A, B) {struct tempStruct { char C[sizeof(A)];} swap_tmp;\    swap_tmp = *( struct tempStruct*) &A;\    *( struct tempStruct*) &A = *( struct tempStruct*) &B;\    *( struct tempStruct*) &B = swap_tmp;}        int main () {                char v1 = 'a';        char v2 = 'b';            SWAP (v1, v2);        cout << v1 << "   " << v2 <<"\n";            float f1 = 45;        float f2 = 123;        SWAP (f1, f2);        cout << f1 << "   " << f2 <<"\n";    }`

 keith12125 4Jul2007 15:39

Re: Swap two variables using macro

>better method is
>usage of
>#define swap(a,b) a^=b^=a^=b;
>
>one line swap without using temporary variable

what exactly does the assignment operator ^= do?

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