Swap with no Temp Variable

When I used to TA for the University of Saskatchewan in our intro C/C++ first year classes I used to try and challenge the students sometimes.  When the assignment rolled out on sorting the students were instructed to swap two variables.  As brand new programmers sometimes something as simple as swapping two variables doesn’t leap out at you.  Of course we just teach them that you need a temp variable and mission accomplished.  Well I always offered bonus marks for anyone who could derive the variable swap with no temp variable.   Years pass, no student ever got back to me with the answer ( they obviously didn’t have Google Fu ).  I find myself writing a routine today that required a swap.  I still remembered the trick:

int main()

int x = 42;
int y = 51236;

printf(“X before swap = %d\n”, x);

x ^= y;
y ^= x;
x ^= y;

printf(“X after swap = %d\n”, x);

return 0;


XOR god mode and fairly easy to remember. X xor Y, Y xor X, X xor Y.  Useful for any POD that is expressed as bytes consistently across architectures.

Needless to say this is a fun trick to blow the minds of long time programmers.

Google’s Coding Style Guide

Regardless of personal preference you will often be forced to adapt to the coding style of someone else.  Generally this will be an enforced style at the company you work for.  Some see this as a minor annoyance.  I personally see this as important and practical.  It helps maintain code readability, this is important for new comers or looking back at your own code.  By making code more readable you also make it more understandable, this makes maintenance even easier.   Decision about style have more impact than arguments like whether braces should be on the same line.

The coding preference which most closely matched my habits turned out to be Google’s C++ Coding Guide.  This made most sense to me as I learned programming starting with C then C++.  In reality I started coding in BASIC on a Commodore 64 but that is a different story.

I find this style guide has a lot of good habits one can derive from it.

Google’s C++ Style Guide

There are some changes to the style I make, here are some important ones:

  • Class members are all prefixed with an underscore
  • Two spaces between functions implementations