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@bhaskar: you are not right the output will be same in any standard compiler of c
and that will be 10 0 0
further ur exaplanation is right

But I really wonder how this code it is returning TRUE for condition (i > j) ?
and this returns TRUE only if I have swap(i,j) call.

Can some one pls explain detailly ?

if (i>j)
temp = i; i = j; j = temp;
if is only for temp = i ; so it will skip that part and run I=J and j=temp which is zero

Its correct ;
Replace that micro . After replacement code will be like this
if(i>j)
temp=a;
a=b;
b=temp;
and if condition is false, therefore only last two statements will be executed.
a(i) will get b(10), b(j) will get temp(0)
finally i=10,j=0;temp=0;

#define swap(a,b)
temp=a;
a=b;
b=temp;
main( )
{ int i, j, temp;
i=10;
j=5;
temp=0;
if( i > j)
swap( i, j );
printf( %d %d %d, i++, ++j, temp);
}

Simple macro substitution
if (i>j)
temp = i; i = j; j = temp;

condition false, so temp will be 0.
That is all.

Actually its "correct" output should be "10 10 0" as gcc shows.

>gcc --save-temps prog.c
Now check the macro expansion in prog.i file.

if(i>j)
temp=i;i=j;j=i;;



Hence,
i=j; /* i becomes 10 */
j=i; /* j becomes 10 */
temp remains as 0