Lecture 10: Elementary Data Types

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What are the 2 things data types all have?
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[1] a set of allowable values; [2] a set of operations on these values.

what are the typical Elementary Data Types
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[1] numeric (integer and floating point), [2] boolean, [3] character, [4] enumerated, and [5] reference or pointer.

what are Enumerated Types
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[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
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[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?
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The declaration: precede a variable name by a “*”: eg int number, *numPtr;

describe the following code " int number, *numPtr; "
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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
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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
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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);"
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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?
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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; "
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*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
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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
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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
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pointers that do not point to a memory location due to deallocation


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