High-Level Programming Languages: C

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Chapter 9

• High-Level Programming Languages C

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Chapter Goals

• Describe the translation process and distinguish
  between assembly, compilation, interpretation,
  and execution
• Name four distinct programming paradigms and name
  a language characteristic of each
• Define the concepts of a data type and strong
  typing
• Describe the structure of a C program

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Chapter Goals

• Construct valid numeric and string expressions
• Construct input and output expressions
• Implement selection statements in C
• Implement loop structures in C
• Implement void and value-return functions
• Define subprogram statements and their use
• Use of nested logic

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Compilers

• High-level languages provide a richer set of
  instructions that makes the programmers life
  even easier
• C, Java, Lisp, Prolog are high-level languages
• Compiler A program that translates a high-level
  language program into machine code
• C is a compiled language

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Compilers
Figure 8.1 Compilation process
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Interpreters

• Interpreter An interpreter translates a statement
  and then immediately executes the statement
• Lisp and Prolog are interpreted languages
• Java is first compiled in an intermediate
  language (called Bytecode) and the Bytecode is
  interpreted.

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Java

• Introduced in 1996 and swept the computing
  community by storm
• Java is compiled into a standard machine language
  called Bytecode
• A software interpreter called the JVM (Java
  Virtual Machine) takes the Bytecode program and
  executes it
• Portability was of primary importance

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C Portability
Figure 8.2 Portability provided by standardized
languages versus interpretation by Bytecode
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Java Portability
Figure 8.2 Portability provided by standardized
languages versus interpretation by Bytecode
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Programming Language Paradigms

• What is a paradigm?
• A set of assumptions, concepts, values, and
  practices that constitute a way of viewing reality

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Programming Language Paradigms

• Imperative or procedural model
• FORTRAN, COBOL, BASIC, C, Pascal, Ada
• Functional model
• LISP, Scheme (a derivative of LISP), and ML

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Programming Language Paradigms

• Logic programming
• PROLOG
• Object-oriented paradigm
• SIMULA and Smalltalk
• C is as an imperative language with some
  object-oriented features
• Java is an object-oriented language with some
  imperative features

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A simple C program
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A C program template
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Introduction to C

• Some components of a C template program
• Comments
• Give information to human readers of code
• Include directive
• The linker includes object code from a library
• Using directive
• Tells compiler to look in a namespace for
  definitions not mentioned in the program

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Virtual Data Storage

• Identifiers names in a programming language
• Keywords have special meanings in C
• C case-sensitive, free-format language
• Data items can be constants or variables

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Some C Standard Data Types

• A declaration of a data item tells
• Whether the item is a constant or a variable
• The identifier used to name the item
• The data type of the item
• Example of a variable integer declaration
• int numb

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Other Data Types

• An array
• Groups together a collection of memory locations,
  all storing data of the same type
• Example
• int Hits12

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Other data types

• Strings
• A string is a sequence of characters
• Example
• string sIntro to CS
• creates a string s that contains Intro to CS

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Statement Types

• Input/output statement
• Input statement
• Collects a specific value from the user for a
  variable within the program
• Output statement
• Writes a message or the value of a program
  variable to the users screen or to a file

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Control Statements

• Types of control mechanisms
• Sequential
• Instructions are executed in order
• Selection or Conditional
• Choice of which instructions to execute next
  depends on some condition
• Looping
• Group of instructions may be executed many times

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Input Statements

• Example
• Pseudocode
• Get value for Radius
• C
• cin gtgt Radius
• cin input stream
• Code for extraction operator (gtgt) and the
  definition of the cin stream come from the
  iostream library and std namespace

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Output Statements

• Example
• Pseudocode
• Print the value of Circumference
• C
• cout ltlt Circumference
• cout output stream
• Code for the insertion operator (ltlt) and the
  definition of the cout stream come from the
  iostream library and std namespace

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Input and Output

• Cin reads from the keyboard and cout writes on
  the screen
• Cin skips the whitespace
• Function get reads one character from an input
  stream
• Stores the character read in a variable of type
  char, the single argument the function takes
• cin.get(character)

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The Assignment Statement

• General form
• Pseudocode
• Set the value of variable to arithmetic
  expression
• C
• variable expression
• Expression on the right is evaluated
• The result is written into the memory location
  named on the left

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Selection Statements

• Default mode of execution sequential
• Selection statement
• Evaluation of a Boolean condition (also called a
  Boolean expression)
• Which programming statement to execute next is
  decided based on the value of the Boolean
  condition (true or false)

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Selection Statements

• Selection statements
• if-else statement
• if (Boolean condition)
• S1
• else
• S2
• if variation of the if-else statement
• if (Boolean condition)
• S1

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Loops

• Looping (iteration)
• The loop body may be executed repeatedly based on
  the value of the Boolean condition
• while statement
• while (Boolean condition)
• S1

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Putting the Pieces Together

• At this point, we can
• Perform input and output
• Assign values to variables
• Direct the flow of control using conditional
  statements or looping
• For a complete program, we need to
• Assemble the statements in the correct order
• Fill in the missing pieces

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Simple example in C

• Problem Write a program that evaluates the
  arithmetic expression A B C 7. Assign an
  arbitrary value to B and C inside the program.
  Print A.
• This corresponds to the pseudo code instruction
• Set A to B plus C minus 7
• Print A
• The C program

//simple example include ltiostreamgt using
namespace std int main() int B10 int
C5 int ABC-7 cout ltlt the value of A is
ltlt A ltlt endl return 0
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Modification 1 of the simple example in C

• MODIFICATION 1 Now I want to ask the user to
  provide for me the values of B, and C. Then I
  want to output the value of A.
• This corresponds to the pseudo code
• Get the value of B and C
• Print the value of A
• cin and cout are the commands for getting data in
  input from the keyboard and printing a data in
  output on the screen
• Note that in computer numbers are converted in
  characters in order to be printed since the
  screen displays ASCII codes!

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Simple example in C Modification 1

• The C program

//simple example Modification 1 include
ltiostreamgt using namespace std int
main() int B, C cout ltlt Insert the value of
B cin gtgt B cout ltlt Insert the value of C
cin gtgt C int ABC-7 cout ltlt the value
of A is ltlt A ltlt endl return 0
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Modification 2 of the simple example in C

• MODIFICATION 2 The second change consists in
  checking if B and C are positive (negative values
  are not accepted). If B and C are not positive,
  force them to be positive (i.e. If B receive -5
  turn B into 5). Then set ABC-7
• This corresponds to the pseudo code
• If (B lt 0) then
• Set B to B(-1)
• If (C lt 0) then
• Set C to C(-1)
• Set A to BC-7

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Simple example in C Modification 2

• The new C program

//simple example Modification 2 include
ltiostreamgt using namespace std int
main() int B, C cout ltlt Insert the value of
B cin gtgt B if (B lt 0)
BB(-1) cout ltlt Insert the value of C
cin gtgt C if (C lt 0) CC(-1) int
ABC-7 cout ltlt the value of A is ltlt A ltlt
endl return 0
Use of IF
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Modification 3 of the simple example in C

• Nested Logic
• MODIFICATION 3 Repeat the previous program 10
  times and each time get new values in input for B
  and C.
• This corresponds to the pseudo code
• Set count to 0
• while (count lt 10)
• execute the program
• Increment count
• endwhile

IF within a WHILE
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Simple example in C Modification 3
//simple example Modification 3 include
ltiostreamgt using namespace std int main()
int B, C int count0 while (count
lt10) cout ltlt Insert the value of B
cin gtgt B if (B lt 0) BB(-1) cout
ltlt Insert the value of C cin gtgt C if (C
lt 0) CC(-1) int ABC-7 cout ltlt the
value of A is ltlt A ltlt endl count
return 0

• The new C program

IF within a WHILE
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Modification 4 of the simple example in C

• MODIFICATION 4 Instead of repeating 10 times I
  want the user to decide if the execution of the
  program must be repeated or not. I will ask the
  user to insert a 0 to stop the program. Any other
  value will force the program to be re-executed.
• This corresponds to the pseudo code
• Set the answer to yes
• While (answer is yes)
• repeat the program
• Ask the user if he/she wants to repeat
• Get the answer
• endwhile

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Simple example in C Modification 4
//simple example Modification 4 include
ltiostreamgt using namespace std int main()
int B, C char answery while
((answer y) (answer Y))
cout ltlt Insert the value of B cin gtgt
B if (B lt 0) BB(-1) cout ltlt Insert
the value of C cin gtgt C if (C lt 0)
CC(-1) int ABC-7 cout ltlt the value of A
is ltlt A ltlt endl cout ltlt Do you want to
repeat this program? (y/n) ltlt endl cin gtgt
answer return 0

• The new C program

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A new problem in C
This Exercise is for you to complete!

• Problem
• Read in a sequence of non-negative numbers, one
  number at a time, and compute a running sum.
• When you encounter the first negative number
  print out the sum of all the non-negative values
  received and stop.

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The pseudocode
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Subprogram Statements

• We can give a section of code a name and use that
  name as a statement in another part of the
  program
• When the name is encountered, the processing in
  the other part of the program halts while the
  named code is executed
• It is implemented by using functions.

Remember?
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Simple example in C Modification 5
//simple example Modification 5 include
ltiostreamgt using namespace std int check(int
x) // function for subprogram if (x lt 0)
xx(-1) int main() int B, C
char answery while ((answer y)
(answer Y)) cout ltlt Insert
the value of B cin gtgt B Bcheck(B) cout
ltlt Insert the value of C cin gtgt
C Ccheck(C) int ABC-7 cout ltlt the
value of A is ltlt A ltlt endl cout ltlt Do you
want to repeat this program? (y/n) ltlt
endl cin gtgt answer return 0

• Break the problem in smaller parts use
  subprograms
• The new C program

Functions