Lecture 10: Elementary Data Types

What are the 2 things data types all have?

[1] a set of allowable values; [2] a set of operations on these values.

what are the typical Elementary Data Types

[1] numeric (integer and floating point), [2] boolean, [3] character, [4] enumerated, and [5] reference or pointer.

what are Enumerated Types

[1] Enumerated types are ordinal type that the possible values can be associated with the set of positive integers (In Java, the primitive ordinal types are integer and char). [2] Enumerated types can be user-defined elementary types

What are Pointer Types

[1] Pointer, or reference, variables have a memory address as their value—we say they “point” to another data item. [2] Pointers are useful in providing a way to manage (allocate and de-allocate) dynamic storage - heap memory.

how is a pointer type declared?

The declaration: precede a variable name by a “*”: eg int number, *numPtr;

describe the following code " int number, *numPtr; "

This means, at runtime: [1] number is associated with a location in memory at which an integer is stored. [2][numPtr is associated with a location in memory at which a memory address is stored.

describe the use of & with pointers

The & operator gives the address of a variable; after executing: number = 42; numPtr = &number; the value of numPtr is the address of variable number.

what is Pointer Dereferencing

We use the pointer dereferencing operator * to access the value pointed to by a vriable

explain the following code "[1] number = 42; numPtr = &number; [2] printf("%d\n", *numPtr);"

We use the pointer dereferencing operator * to access the value pointed to by numPtr: printf("%d\n", *numPtr); which here will display 42.

What does null mean?

A special value null (null is actually stored as a 0) is assigned to any pointer variable to signify that it doesn’t point to any location.

explain the following code " int *p; int *q int a = 100; p=&a; *q = *p; q = p; "

*q = *p; This copies the contents (100) of the memory location pointed by p to q. whereas q = p; copies the value (a memory address) of p to q.

what does calloc do

calloc allocates a block of memory of "n elements" of "size" bytes each and initializes contents of memory to zeroes. It contain info for memory organisation.

what does malloc do

malloc allocate specified size (no organisation info) of memory but does not erase them, therefore the memory may contain garbage values.

what are Dangling Pointers

pointers that do not point to a memory location due to deallocation