Kate Gregory with material from Deitel and Deitel

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Week 3

• Questions from Last Week
• Hand in Lab 1
• Arrays
• Pointers
• Strings
• Lab 2

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(No Transcript)
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Arrays

• A collection of items, all the same type, that
  can be treated as a unit or one at a time
• 10 integers
• 5 floating point numbers
• 100 characters

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Memory arrangement
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Declaring Arrays

• int scores10
• char letters26
• float ratios5
• Size is fixed

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Using Array Elements

• scoresi
• cout ltlt letters4
• ratio2 4.7

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No bounds checking in C

• int scores10
• for (int i0 ilt20 i)
• scoresi 100
• Youre the programmer!

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Bug prevention

• define MAXSCORES 10
• int scoresMAXSCORES
• for (int i0 ilt MAXSCORES i)
• scoresi 100
• More readable, less error-prone
• Cant use a variable when declaring the array

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Initializers

• int n 5 1, 2, 3, 4, 5
• Or just
• int n 1, 2, 3, 4, 5

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Passing arrays to functions

• int total(int a)
• // ...
• int numbers 1,2,3,4,5
• int x total(numbers)

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Taking arrays in functions

• int total(int a)
• int tot 0
• int limit sizeof(a) / sizeof(int)
• for (int i0 iltlimit i)
• tot ai
• return tot

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Pointers

• Address of a variable in memory
• They have a type
• int p
• char s

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operator

• (address operator) gets address of operand
• int y 5
• int yPtr
• yPtr y // yPtr gets address of y

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operator

• (indirection/dereferencing operator)
• Gives access to what the pointer points to
• yptr returns y (because yptr points to y)
• can be used for assignment
• yptr 7 // changes y to 7
• and are inverses
• They cancel each other out

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Pointers and Arrays

• int scores10
• x scores3
• x
• y scores
• y

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Pointers and Arrays

• scores1 2
• int p scores
• p
• p 2
• Adding is cheaper than multiplying

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String Array of Characters

• char word K,a,t,e,\0
• char word Kate
• Note that \0 and 0 are different.
• Null terminated strings

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Accessing characters

• cout ltlt word
• cout ltlt word0
• word0 L
• Note single quotes

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Strings and pointers

• for (char p word p p)
• cout ltlt p

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Arrays of Pointers

• char suit 4 "Hearts", "Diamonds",
  "Clubs", "Spades"
• Strings are pointers to the first character
• char each element of suit is a pointer to a
  char
• The strings are not actually stored in the array
  suit, only pointers to the strings are stored
• suit array has a fixed size, but strings can be
  of any size

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Arrays of Pointers
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Multi Dimensional Arrays

• Tables with rows and columns (m by n array)
• Like matrices specify row, then column

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Multi Dimensional Arrays

• Initialization
• int b22 1, 2 , 3, 4
• Initializers grouped by row in braces
• If not enough, unspecified elements set to zero
• int b22 1 , 3, 4
• Referencing elements
• Specify row, then column
• cout ltlt b01

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String Library

• Functions originally from C
• strlen
• strcat
• strcpy
• strcmp
• strtok
• Dont reinvent the wheel

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For Next class

• Complete Lab 2
• Late penalty is TERRIBLE
• Read chapter 6