Processing Arrays

1
Processing Arrays

• Foundation Programming With C

Hang in there, retirement is only fifty years
away.
2
Quiz

• What will the following code output?

include ltstdio.hgt int main() int i,
sum0 for(i0 ilt11 i2) sumi prin
tf("i\n", sum)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

3
Quiz

• Solution
• 2 4 6 8 10 30

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

4
Quiz

• What type of loop is most applicable to the
  following problems (please select one option per
  problem)?
• Initialising an array of 10 elements to zero
• Sentinel Controlled Loop
• Counter Controlled Loop

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

5
Quiz

• Reading in numbers from a user until they enter
  the value 0 (zero).
• Sentinel Controlled Loop
• Counter Controlled Loop
• Reading in 10 numbers from a user
• Sentinel Controlled Loop
• Counter Controlled Loop

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

6
Quiz

• Answers
• Counter Controlled Loop (b)
• Sentinel Controlled Loop (a)
• Counter Controlled Loop (b)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

7
Quiz

• The following piece of code attempts to sum
  numbers entered by a user until the value 9999 is
  encountered. The solution below compiles but
  shows a number of errors when it is run.
  Describe the errors in words?

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

8
Quiz
include ltstdio.hgt int main() int sum int
input while(input!9999) printf("Enter
number ") scanf("i", input) sum
input printf("i\n", sum)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

9
Quiz

• Answers
• sum is not initialised, the sum will be incorrect
  sometimes, but not always
• input is not initialised or primed before while
  test
• The sentinel will be included in the sum
• Input from user is not validated

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

10
Quiz

• In the following code there are a number of boxes
  where comments are to be placed. Write a comment
  for each box that describes the purpose of the
  code below it.
• The function getValidPositiveInteger() is
  declared on a second slide.

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

11
Quiz
int main() int max, int input, int i //
max 0 // for(i0 ilt5 i)
// input getValidPositiveInteger()
// if(input gt max) max
input // printf("i\n", max)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

12
Quiz
int getValidPositiveInteger() int input int
numbersReadIn // printf("Enter a positive
integer ") numbersReadIn scanf("i",
input) // while(numbersReadInlt1
inputlt0) // scanf("\n") scanf
("c") // printf("Invalid input.
Enter a positive integer ") numbersReadIn
scanf("i", input) // return
input

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

13
Concepts Covered
Standard Input
Types of Loops
Storing Numbers
scanf()
The while Loop
Arrays for Categories
Reading Strings
The for Loop
Searching
Scansets
The do-while Loop
Sorting
Ignoring Input
Identifiers and Loops
Multidimensional Arrays

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

Clearing Standard Input
When to Use What Loop
Command Line Arguments
File Redirection
Sentinel Controlled Loop
Validating Input
Finding Min/Max
Week 7
Week 8
Week 9
14
Storing Numbers

• Variables good for single pieces of data
• With arrays and loops we can
• Store and process multiple pieces
• In a uniform manner

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

15
Storing Numbers

• Example Part 1

include ltstdio.hgt const int MAX_LENGTH
5 int main() int arrayMAX_LENGTH int
i int sum 0 int mean 0 for(i0 i lt
MAX_LENGTH i) printf("Enter number i ",
i1) scanf("i", arrayi) sum
arrayi

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

16
Storing Numbers

• Example Part 2

... if(MAX_LENGTH!0) mean
sum/MAX_LENGTH printf("Mean is i\n",
mean) printf("Numbers greater than mean
are...\n") for(i0 i lt MAX_LENGTH i)
if(arrayi gt mean) printf("i\n",
arrayi)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

Enter number 1 4 Enter number 2 2 Enter number
3 5 Enter number 4 3 Enter number 5 1 Mean is
3 Numbers greater than mean are... 4 5
17
Arrays for Categories

• We can also use arrays to
• Track if items from a list have been encountered,
  or
• How many times an item has appeared
• Example
• Counting how many times each letter of the
  alphabet appears in a sentence...

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

18
Arrays for Categories
int letters26

• We could declare an array where
• letters0 will record how many times 'a' has
  been used,
• letters1 will record how many times 'b' has
  been used, and so on

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

19
Arrays for Categories

• Initialise before beginning

// Initialise all array elements to 0 for(i0
ilt26 i) lettersi 0

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

20
Arrays for Categories

• Read in and categorise each character until
  newline

// Process the user input printf("Please input a
sentence...\n") scanf("c", inputLetter) while(
inputLetter ! '\n') if(isalpha(inputLetter))
letterstolower(inputLetter)-'a' scanf
("c", inputLetter)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

21
Arrays for Categories

• Report how many times each character appeared

// Output occurences of letters for(i0 ilt26
i) if(lettersi gt 0) printf("c i\n",
'a'i, lettersi)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

Enter a sentence... My name is Michael a 2 c
1 e 2 h 1 i 2 ...
... l 1 m 3 n 1 s 1 y 1
22
Arrays for Categories

• Set Count plan

CCL or SCL

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

Input Item to Count
Match Item to Array Elementand Increment Element

23
Searching in Arrays

• We can count the number of times a value appears
  in an array

int count(int target, int array, int length)
int count0 // Counts appearances of
target int i // Iterative counter //
Compare each element in the array for(i0
iltlength i) if(arrayi target)
count return count

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

24
Searching in Arrays

• With arrays and repetition we can now search
  through arrays

bool search(int target, int array, int length)
bool found false // Boolean search
flag int i 0 // Iterative
counter // Search until found or end of
array while(!found iltlength) // Match
array element to target value found
arrayitarget i return found

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

25
Sorting Values in Arrays

• Many sorting algorithms
• Bubble Sort
• Start at beginning
• Compare adjacent pairs
• If out of order swap
• Repeat n-1 times where n is the size of the array

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

26
Sorting Values in Arrays

• Example

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

7
8
2
5
4
2
8
8
5
8
4
7
2
5
4
8
2
7
7
5
7
4
2
5
4
7
8
4
5
27
Multidimensional Arrays

• An array of arrays
• Declaration example

int array35

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

array03
array11
row 0
3
row 1
1
row 2
4
array24
28
Command Line Arguments

• The main() function can have either none or two
  arguments as follows

int main(int argc, char argv) ...

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

The number of arguments including the executable
name
An array of strings, one string per argument
29
Command Line Arguments

• Example

include ltstdio.hgt int main(int argc, char
argv) int i printf("Argument count
i\n", argc) for(i0 iltargc i)
printf("i s\n", i, argvi)

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

a.out hello there Argument count 3 0 a.out 1
hello 2 there
30
Checking Comm. Line Args

• Check whenever command line arguments are needed

include ltstdio.hgt int main(int argc, char
argv) // Check for the correct number of
arguments if ( argc lt 2 ) printf("USAGE s
guesses\n", argv0) exit(1) // Rest of
program ...

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

31
Naming Executables

• The -o switch allows naming
• Using DOS/Windows append .exe

g mygrep.cpp o mygrep

• Quiz
• Concepts
• Storing Numbers
• Categories
• Searching
• Sorting
• Multi-D arrays
• Command line args

gpp mygrep.cpp o mygrep.exe