Question

Suppose a variable pa is always declared as one of two ways:

double * pa

OR

double pa

Can we create an IF statement that does the following

IF (pa is a pointer)
{ pa[0] = 1
}

ELSE
{ pa = 1}

EDIT:

Please see How to find out if a pointer array has been filled in C++/C for the follow up question

Answer 1

Not directly, no. Suppose there were a way to do this, something like

if (__IS_POINTER(pa) {
    pa[0] = 1;
}
else {
    a = 1;
}

What happens if pa isn’t a pointer? You still have that pa[0] = 1; statement in your program, and it’s illegal, so the compiler is going to reject your program.

You might in principle be able to do a compile-time test:

#if __pa_IS_A_POINTER
pa[0] = 1;
#else
a = 1
#endif

but the power of the C++ preprocessor is very limited; it has no way to test the type of a variable or expression.

If you had this capability, what would you do with it? Tell us what your actual goal is.