check if app is running in 64 bit

There are two ways to determine this: at runtime (i.e. in your running code), and at compile time (i.e. before the code is compiled). Let’s take a look at both options.

Runtime Check
// testing for 64bit at runtime

if (sizeof(void*) == 4) {
self.textLabel.text = @"You're running in 32 bit";

} else if (sizeof(void*) == 8) {
self.textLabel.text = @"You're running in 64 bit";
}
Determines the size of a pointer.

Compile Time Check
#if __LP64__
// you're running 64bit
#else
// you're running 32bit
#endif
Asks the compiler which architecture it compiles for.