CIS 101: Computer Programming and Problem Solving Lecture 9

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CIS 101 Computer Programming and Problem
SolvingLecture 9

• Usman Roshan
• Department of Computer Science
• NJIT

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C functions

• Function definition
• ltreturn valuegt ltfunction_namegt (
• ltarg1_typegt ltarg1gt,
• ltarg2_typegt ltarg2gt,
• ,
• ltargn_typegt ltargngt)
• For example,
• int myadd(int x, int y)l
• int max(int x, int y)

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C functions

• Compiler goes from top to bottom. So, either
• Declare function before main() and then define it
  anywhere in the file
• Or define it before main()

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myadd function
First define function
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Same function with different parameters--overloadi
ng
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Passing arrays as arguments
Define function before main
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Program output
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Pointers and reference
Returns memory location of the variable

• int x2 int y
• y x

Memory
x
100
2
2
y
x
Memory is organized into cells. Lets say x is in
cell number 100
y is a pointer to an integer. We set it to point
to x which means it will now contain the memory
location of x.
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Pointers and references
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Dynamic memory allocation---creating and deleting
arrays of arbitrary size

• int x
• x new int1
• We first create an array pointer and then
• create space in memory for one integer it
• can point to.

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Pointers and reference

• int x
• x new int1
• x 2

Memory
50
2
x
x
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Pointers
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Output of pointer program
x is a pointer to a location in memory which is
why it shows up in HEX
The memory location x points to contains 2.
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Dynamic arrays

• int x
• x new int(3)
• x0 2
• x2 4
• x3 6

Memory
50
2
4
6
x0
x
x1 x2
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Dynamic arrays
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Dynamic arrays

• Memory defined using new must be cleared up using
  delete. Otherwise your program may use up ALL the
  memory.
• int x new int10
• .
• .
• delete x

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Passing variables by value
A new variable is created that contains a copy of
x
This means the value in the original variable is
unchanged.
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Program output
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Passing variables by reference
means we are receiving a reference to the
original variable and it can be modified.
Now the value in the original variable x can be
modified.
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Program output
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Two dimensional arrays

• 2D arrays are defined as
• int A1010
• This allocates space for a 2-D array of
• dimension 10 times 10, with un-initialized
• values.
• You can also do
• int a10
• This creates an array of 10 integer pointers for
• which space has to be allocated using new.

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Lab problems

• Power function to compute xy
• Swap function to interchange two numbers
• Copy array function
• Problems from midterm