Interview answers verified by specialists.

Find interview questions and answers on this website:

See right interview answers on 30 common job interview questions

Why can't constant values be used to define an array's initial size?

There are times when constant values can be used and there are times when they can't. A C program can use
what C considers to be constant expressions, but not everything C++ would accept.

When defining the size of an array, you need to use a constant expression. A constant expression will always
have the same value, no matter what happens at runtime, and it's easy for the compiler to figure out what
that value is. It might be a simple numeric literal:

char    a[ 512 ];

Or it might be a "manifest constant" defined by the preprocessor:

#define MAX     512
/* ... */
char    a[ MAX ];

Or it might be a sizeof:

char    a[ sizeof( struct cacheObject ) ];

Or it might be an expression built up of constant expressions:

char    buf[ sizeof( struct cacheObject ) * MAX ];

Enumerations are allowed too.

An initialized const int variable is not a constant expression in C:

int     max = 512;      /* not a constant expression in C */

char    buffer[ max ];  /* not valid C */

Using const ints as array sizes is perfectly legal in C++; it's even recommended. That puts a burden on C++
compilers (to keep track of the values of const int variables) that C compilers don't need to worry about.
On the other hand, it frees C++ programs from using the C preprocessor quite so much.

Do you know that?

biggest challenge for 17.3% freelancers is papaerwork, legal and accounting issues Next


Fast Payments
Payoneer sing up to get free