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How do you make a verbatim copy of a file, including all the whitespaces ? ... For a verbatim copy. read and record every character, including whitespace. ... – PowerPoint PPT presentation

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Title: A1256654067XtcnG

1

CS 215 Introduction to Programming with
C Instructor Eric Sedgwick
2
This Time

Program design and testing
Input and Output streams
file I/O
Functions calling functions
recursion

3
This Time

I/O streams (continued)
character I/O
Introduction to Arrays (Chapter 9)

4
Question

How do you make a verbatim copy of a file,
including all the whitespaces ?
Can you do this with ltlt and gtgt ?

5
Recall the purpose of I/O

To convert between characters and other data
types
gtgt does this automatically
gtgt forgets whitespace in the input stream
Spaces
Newlines (\n)
Tabs (\t)

6
For a verbatim copy

read and record every character, including
whitespace.
To read every character, use the input stream
member function get
char symbol
cin.get(symbol) // call-by-ref
There is a corresponding output stream function
put, but we dont really need it.

7
What are c1,c2,c3,c4?

Input stream in_stream
Aa
Bb
Execute this code
char c1,c2,c3,c4
in_stream.get(c1)
in_stream.get(c2)
in_stream.get(c3)
in_stream.get(c4)

8
Pitfall

Forgetting about the newline character, \n.
It can be used to your advantage to detect the
end of the line. You will need this for your hw!

9
The eof() function

Returns true when you have tried to read past the
last thing in the file. If true you have already
one too many characters.
To copy from in_stream to out_stream
in_stream.get(symbol)
while (!in_stream.eof())
out_stream ltlt symbol
in_stream.get(symbol)
verbatim_copy.cpp

10
Predefined character functions

Some character functions, more on pp. 918-919
ctoupper(z) // cZ
ctolower(H) // ch
islower(z) // returns true
isupper(b) // returns false
isalpha() // returns false
isdigit(c) // returns false
isspace() // returns false
Requires include ltcctypegt

11
Careful !

toupper and tolower return ints that can be
converted to chars
char c
c tolower(Z)
cout ltlt c Output z
cout ltlt tolower(Z) Output 90
cout ltlt char(tolower(Z)) Output z

12
split_copy.cpp

How do we change verbatim_copy.cpp to put
letters in one file and numbers in another ?
(Everything else should go to both)

13
gtgt vs. get

When should you use gtgt and when should you use
get ?
Use get when you care about every character in
the input file (especially spaces).
Be careful about \n, \t etc.
Otherwise use gtgt

14
Arrays
15
Problem

Write a program that
gets n (say 5) numbers from the user,
calculates the minimum of those numbers, and
Prints out how far each is above the minimum
Example
Input 65 66 63 70 69
Output 2 3 0 7 6
Problem Need to access each data item twice.

16
Solution?

This would work (if you had a min(a,b)function)
int a0,a1,a2,a3,a4
cin gtgt a0 gtgt a1 gtgt a2 gtgt a3 gtgt a4
minimum min(a0,min(a1,min(a2,min(a3,a4))))
cout ltlt a0-minimum
cout ltlt a1-minimum
Problem
What if you wanted to compute for 100 numbers?
Not practical to extend this code.

17
Solution

Use an array!int score5
This declares 5 integer variables, with names
score0,score1,score2,score3,score4
The base type of the array is int.
The size of the array is 5.
Very Important! Arrays are numbered 0,..,size-1

18
Indexing

Each item can be treated individually as an
integer variable by supplying an index, the
number of the particular array item you want to
access
score05
score1 score2-1 score3
cout ltlt score3 ltlt score1
The index can be a variable, it is evaluated
student3
scorestudent 99 // same as
score3 99

19
Terminology

scoresi1 7
scores is the name of the array
scoresi1 is an element of the array
i1 is the index of that array element
7 is the value of that element of the array

20
Arrays and Loops

To read in all 5 numbers, you could (dont do
this)
cin gtgt score0 gtgt score1 gtgt score2
gtgt score3 gtgt score4
Or, use a loop. This is more powerful.
int count
for(count0countlt5count)
cin gtgt scorecount
Be consistent, always write it like this
for(count0countltsizecount)

21
Minimum.cpp

Gets n (say 5) numbers from the user,
Calculates the minimum of those numbers, and
Prints out how far each is above the minimum
What happens if we read 6 numbers?

22
Arrays in Memory

To declare a non-indexed variable in memory, two
pieces of information are needed
Address, the first byte of variable
Type, determines how many bytes are used
For indexed variables (arrays), three items are
needed
Address, the first byte of variable
Type, determines how many bytes are used for each
element of the array.
Size, number of elements in the array.

23
Arrays are dangerous

They are dangerous because of the way that they
are stored and referred to in memory.
You can address memory that you shouldnt.
This is called an index out of range error
Unlike previous errors, this can have
consequences outside your program
Why isnt the compiler more careful?
Compile-time vs. run-time checking

24
Arrays in memory
Addresses

stored contiguously
Variables are referenced by their addresses
E.g, Score2 is the int variable that is
2length(int) bytes further than score0.

4021
Score0
4023
Score1
4025
Score2
4027
Score3
4029
Score4
Score5
Score6
Other stuff, what?
Very very bad!!
25
Programming Tip

Make the maximum array size a global constant and
always refer to this constant.
Makes it easy to adapt your program for larger
(smaller inputs)
E.g.,
const int MAX_SIZE 100
double scoreMAX_SIZE
for(i0iltMAX_SIZEi)
cin ltlt scorei

26
Initializing arrays

Elements one at a time. Suppose MAX_SIZE 3
int ageMAX_SIZE
age0 21
age1 19
age2 35
All together, this is equivalent
int ageMAX_SIZE 21,19,35
With a loop
For(int i0iltMAX_SIZEi)
agei 0

27
Setting arrays equal

This is no good
int scoreMAX_SIZE, gradeMAX_SIZE
Score grade // will not compile
Score grade // still no good
Score0 grade0 // fine, but 1 element
You must step through the arrays with a loop
int scoreMAX_SIZE, gradeMAX_SIZE
for(i0iltMAX_SIZEi)
scorei gradei // element by element

28
Arrays and functions

Array elements as call-by-value arguments
Array elements as call-by-reference arguments
Entire arrays as arguments

29
Array elements as call-by-value arguments

square.cpp
This is nothing new, each array element is a
variable of the given type.

30
Class Exercise

Write a stat program that
Reads in a list of scores from the user
calculates the minimum score
Calculates the average
Calculates the maximum score
Each of these tasks should be functions
stat.cpp

31
Entire arrays as arguments

When passing an array, the parameter list must
contain two items. In our examples (stat.cpp)
num an array parameter
Brackets signify an array
Similar to a call-by-ref, the base type of the
array and address to the 1st element are passed
to the function
size, a call-by-value parameter
The number of items to be manipulated
Necessary to prevent index out of range

32
const parameter modifier

If your function does not modify the value of the
array, have the compiler make sure that it does
not happen accidentally.
int min(const int num, int size)
Make the compiler work for you

33
Class Exercise