Pointers Part 4-Fundamentals of Computer-Lecture Slides, Slides of Computer Fundamentals

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Pointers and Arrays

What are pointers for?

• Here are some common uses:
  • Accessing array elements
  • Passing arguments to a function when the function needs to modify

the original argument

• Passing arrays and strings to functions
• Obtaining memory from the system
• Creating data structures such as linked lists

Declaration of a Pointer Variable

y [ 0 ] (^) [0]

[1]

[2]

[3]

[4]

[5]

[6]

[7]

[8]

[9]

yptr

int y [ 10 ] ;

int *yptr ;

yptr = y ;

yptr is a pointer to integer

int y [ 10 ] ;

int *yptr ;

yptr = y ;

yptr ++ ;

The Relationship Between

Pointers and Arrays

• Element b[ 3 ]
  • Can be accessed by *( bPtr + 3 )
    • Where n is the offset. Called pointer/offset notation
  • Can be accessed by bptr[ 3 ]
    • Called pointer/subscript notation
    • bPtr[ 3 ] same as b[ 3 ]
  • Can be accessed by performing pointer arithmetic on the array

itself

*( b + 3 )

Pointer Expressions and Pointer Arithmetic

• Arithmetic operations can be performed on

pointers

• Increment/decrement pointer (++ or --)
• Add an integer to a pointer( + or += , - or -=)
• Pointers may be subtracted from each other
• Operations meaningless unless performed on an array

• Subtracting pointers
  • Returns number of elements from one to the other. If vPtr2 = v[ 2 ]; vPtr = v[ 0 ];
  • vPtr2 - vPtr would produce 2
• Pointer comparison ( <, == , > )
  • See which pointer points to the higher numbered array

element

• Also, see if a pointer points to 0

Pointer Expressions and Pointer Arithmetic