Toggle an Integer Between 1 and 0

Posted on April 28, 2009 by John Muchow in C

If you ever come upon a need to toggle an integer value between 1 and 0, consider using the bitwise exclusive-OR (^) operator in C to get the job done.

In a recent application I wrote a method with one parameter, an integer, that is expected to be 1 or 0. In creating a demo of the application I wanted to pass in alternating values of 1 and 0 as part of a test for a specific use case. Instead of using an if statement in the calling method to decide when to send a 1 or 0, I wrote something similar to the code below:

- (void)someMethod
{
  static int x = 0;
 
  // Toggles 1 to 0 and 0 to 1 using xor
  x ^= 1;
 
  // Call the method that expects a 1 or 0
  [methodCallHere toggle:x];
}

More often than not, exclusive-OR (^), AND (&) and inclusive-OR (|) are consider a bit-level operations (see this post on bitfields). However, there are times when these operators work equally well with integer values.

Comments

5 Responses to “Toggle an Integer Between 1 and 0”

Mike says:

April 28, 2009 at 3:25 pm

Pretty handy to use this with the bitfields from a previous post of yours.

typedef struct {
unsigned preLoaded;
unsigned saveState;
unsigned saveLoginName;
} SomeStatus;

SomeStatus status;
status.preLoaded = 1;
status.saveState = 0;
status.saveLoginName = 1;

status.preLoaded ^= 1;

if( status.preLoaded == 0 )
NSLog(@”preloaded is off”);
else
NSLog(@”preloaded is on”);

if( status.saveState == 0 )
NSLog(@”saveState is off”);
else
NSLog(@”saveState is on”);

if( status.saveLoginName == 0 )
NSLog(@”saveLoginName is off”);
else
NSLog(@”saveLoginName is on”);

[Reply]
seventoes says:

April 28, 2009 at 3:27 pm

Same as using a bool and doing..

BOOL someBool = NO;

someBool = !someBool;

//someBool is now YES

[Reply]
john says:

May 1, 2009 at 1:22 pm

Another way is this:

x = 1 – x;

If x is 1, it is now 0. If it was 0, it’s now 1. Pretty much the same thing as using XOR, but much simpler to understand.

[Reply]
Pascal says:

May 4, 2009 at 4:11 am

If you’re using the int as a kind of flag…

You might remember your end of last year: http://iphonedevelopertips.com/objective-c/of-bool-and-yes.html

BOOL is nothing else than a signed char, and YES is defined as 1 (NO is 0), you can even write:

static int x = 0;

// Toggles 1 to 0 and 0 to 1 using !
x = ! x;

[Reply]
root says:

March 12, 2010 at 4:03 am

bitwise operations like ^ tend to be significantly faster than other operations.

[Reply]