Data commit

Task/Pointers-and-references/XPL0/pointers-and-references.xpl0

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+\Paraphrasing the C example:
+\This creates a pointer to an integer variable:
+int Var, Ptr, V;
+Ptr:= @Var;
+
+\Access the integer variable through the pointer:
+Var:= 3;
+V:= Ptr(0);     \set V to the value of Var, i.e. 3
+Ptr(0):= 42;    \set Var to 42
+
+\Change the pointer to refer to another integer variable:
+int OtherVar;
+Ptr:= @OtherVar;
+
+\Change the pointer to not point to anything:
+Ptr:= 0;        \or any integer expression that evaluates to 0
+
+\Set the pointer to the first item of an array:
+int Array(10);
+Ptr:= Array;
+\Or alternatively:
+Ptr:= @Array(0);
+
+\Move the pointer to another item in the array:
+def IntSize = 4;        \number of bytes in an integer
+Ptr:= Ptr + 3*IntSize;  \pointer now points to Array(3)
+Ptr:= Ptr - 2*IntSize;  \pointer now points to Array(1)
+
+\Access an item in the array using the pointer:
+V:= Ptr(3);     \get third item after Array(1), i.e. Array(4)
+V:= Ptr(-1);    \get item immediately preceding Array(1), i.e. Array(0)
+]