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─────C/C++ Language─────────────────────────────────────────────────────────
 
     In both C and C++, the const keyword specifies that a variable's
     value is constant and tells the compiler to prevent the programmer
     from modifying it. For example:
 
          const int i = 5;
 
          i = 10; // Error
          i++;    // Error
 
     In C++, you can use the const keyword instead of the #define
     preprocessor directive to define constant values. Values defined
     with const are subject to type checking, and can be used in place
     of constant expressions. For example, in C++ you can specify the
     size of an array with a const variable as follows:
 
        const int maxarray = 255;
        char store_char[maxarray];  // Legal in C++; illegal in C
 
     In C, constant values default to external linkage, so they can
     appear only in source files. In C++, constant values default to
     internal linkage, which allows them to appear in header files.
 
     The const keyword can also be used in pointer declarations. For
     example:
 
        char *const aptr = mybuf;  // Constant pointer
 
        *aptr = 'a';       // Legal
        aptr = yourbuf;    // Error
 
        const char *bptr = mybuf;  // Pointer to constant data
 
        *bptr = 'a';       // Error
        bptr = yourbuf;    // Legal
 
     You can use pointers to constant data as function parameters in
     order to prevent the function from modifying a parameter passed
     through a pointer.
 
     See: define
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