Basics of C++ Language

• BYTE MyByte;
  Allocate a byte (8 bit unsigned number, range 0 / 255
  
  
• BYTE VetMyArray[500];
  Allocate a vector of 500 bytes
  
  
• char MyText[100];
  Allocate 100 bytes where we can store a text
  
  
• char MyText[] = "Warning: you have no more ammos!";
  Allocate the memory required to host the text.
  In this case we initialized our vector of char, and we omitted the number_of_items because the compiler computes the right value counting the character of our text.
  
  
• char *pText;
  Allocate a dword to host a memory address (pointer) the will point to a text string
  
  
• WORD MyNumber;
  Allocate 2 bytes for 16 bit unsigned numbers
  
  
• short MyNumber;
  Allocate 2 bytes for 16 bit signed numbers
  
  
• int MyNumber;
  Allocate 4 bytes for a 32 bit signed number
  
  
• DWORD MyNumber;
  Allocate 4 bytes for a 32 bit unsigned number
  
  
• float MyFloatNumber;
  Allocate 4 bytes for a floating point number
  
  
• float MyFloatConst=1.5393;
  Allocate 4 byte for a floating point number and initialize its value to 1.5393
  
  
• StrItemTr4 MyStruct;
  Allocate the bytes to host a StrItemTr4 structure
  
  
• StrItemTr4 *pMyStruct;
  Allocate 4 bytes to host the address pointing to a StrItemTr4 structure
  

• The instruction "pMyPointer = MyVect;" seems wrong, because it is missing the "&" operand to read the address of MyVect variable.
  
  
• In the istruction "pMyPointer[3]=0;" we are using a pointer omitting the "*" in front of its name. We are using it like it was a vector, since we used the squared parenthesis to set the index to use to read a cell of a vector.
  

1. Why, in this case, have we used the & operator?
   In previous code we showed the instruction:
             pMyPointer = MyVector;
   omitting the "&" and explaining that it was correct in this way.
   Why now have we used the & operator?
   Because when we use the squared parenthesis with the index ("[6]") it is not more a pointer but only a single variable (a word in that case).
   For this reason when we wish having a pointer refered to a single cell of a vector we have newly to use the "&" operator.
   Pratically it's like saying that only the single (alone) name of a vector is a pointer but not when we use it in the form "MyVect[4]"
   
   
2. Other question is: what is the the benefit of the instruction?:
             pMyPointer = &MyText[6];
   Well, in above case, probably nothing, but in other cases it is useful memorize the position of some item (like a substructure) contained in a bigger zone whom we have only the pointer to the starting address.
   In above case now the pMyPointer will point to the text "world"
   

• Change the declaration of littler variable.
  In this case we should change the declaration from:
  WORD Result;
  to new decalarion:
  DWORD Result;
  
  
• Other chance is to say to the compiler that you know that situation and you don't want to be alerted newly.
  You can realize this, typing a casting operator where you convert, temporary the bigger variable in a littler size to do understand to the compiler that you know very well that situation.
  In this way you edit the istruction:
  
  Result = Alfa+1;
  
  in this way:
  
  Result = (WORD) Alfa+1;
  

char *ControlValues(int *pVetValues)

{

    int i;

    int CurrentValue;

    char *pMessage;

    pMessage = "That's ok";

    for (i=0;i<100;i++) {

         CurrentValue = pVetValues[i];

         if (CurrentValue < 0) {

               pMessage = "ERROR: invalid value less than zero";

               break;

          }

          // other code to manage the currentvalue

    }



return pMessage;

}