16. Working with Simple Variables, PTR operator

• CPU has instructions to copy, move, and sign-extend integer values.

• These instructions require operands to be the same size.

• However, we may need to operate on data with size other than that originally declared.

• The PTR operator forces expression to be treated as the specified type:

          .DATA
          num  DWORD   0
  
          .CODE
          mov     ax, WORD PTR num[0] ; Load a word-size value from
          mov     dx, WORD PTR num[2] ; a doubleword variable
  

  PTR operator re-casts the DWORD-sized memory location pointed by num[ index ] expression into a WORD-sized value.