Problem
How to swap 2 variables using macro?
Solution
#define swap(type,a,b) type temp;temp=a;a=b;b=temp;
Now, think what happens if you pass in something like this
swap(int,temp,a) //You have a variable called "temp" (which is quite possible).
This is how it gets replaced by the macro
int temp;
temp=temp;
temp=b;
b=temp;