Chapter 1: Introduction - II

Chapter Goals

• To learn about higher-level programming languages
• To compile and run your first C++ program
• To recognize syntax and logic errors

Programming Languages

• A special computer program, a so-called compiler, translates the higher-level description into machine instructions for a particular processor.
  
• Compilers follow strict conventions regarding programming language use. When a compiler reads programming instructions (expressions, operators, statements) in a programming language, it will translate them into machine code only if the input follows the language conventions exactly.
  
• Strict rules prevent more disastrous errors that could arise should the compiler "guess."
• There are many (hundreds of) programming languages.
• Differences in programming languages are sometimes slight, but at other times substantial.
  • C++:
    

    if (int_rate > 100) message_box("Interest rate error");

  • Pascal:
    

    if int_rate > 100 then message_box('Interest rate error');

Programming Language Design and Evolution

(Specific and General Purpose Languages)

• Many programming languages are created with a specific purpose.
  • database processing.
  • "artificial intelligence."
  • multimedia processing.
• Special-purpose languages are not used much beyond their area of specialization.
• General purpose languages can be used for any task.
  • Pascal: designed as a teaching language (purposefully kept simple).
  • C: developed to be translated efficiently into fast machine code, with a minimum of housekeeping.
  • C++: adds "object oriented programming" aspects to C.

Programming Language Design and Evolution

(Incremental Growth)

• C and C++ are languages that grew in increments; as the users of the language perceived shortcomings, they added features:
  • 1972 - original design of C by Dennis Ritchie (link). Many compilers add different features, sprouting dialects of C.
  • 1985 - Bjarne Stroustrup of AT&T adds object oriented features to C, creating C++.
  • 1989 - ANSI standard of C developed to resolve differences among the several version of C.
  • 1998 - Standards developed for most recent version of C++.
• Grown languages tend to be messy; different features are added by people with different tastes.
• Grown languages are modified in a hurry to solve a specific need, without considering the consequences.
• Grown languages accumulate a patchwork of features that do not necessarily interact well together.
• Grown languages have an edge in the marketplace (C++ allows programmers to use new features without throwing away old C code).
• The purpose of our course is not to teach you all of C++ but to use C++ for teaching you the art and science of writing computer programs!
  

Programming Language Design and Evolution

(Planned Languages)

• Planned languages (such as Pascal and Ada) are carefully designed to anticipate the needs of future users.
• More thought goes into planned languages.
• Features of planned languages tend to be more related to one another.
• Designers pay more attention to readability and consistency.
• Well designed languages are easier to use and learn.

Compiling a Simple Program ("Hello, World!")

• C++ is case sensitive
• C++ has freeform layout
  • Good taste dictates that you use readable program layout.

Syntax

header files
using namespace std;
int main()
{
   statements
   return 0;
}

#include <iostream>
using namespace std;
int main()
{
   cout << "Hello, World!\n";
   return 0;
}

Compiling a Simple Program

• #include<iostream> - read the file iostream that contains the definition for the stream input/output package.
• using namespace std; - all names in the program belong to the "standard namespace"
• int main () { ... } defines a function called main. A function is a collection of instructions that carry out a particular task.
• The statements (instructions) inside the body (inside the curly braces { ... }) of the main function are executed one by one.
• Each statement ends with a semicolon ;
• The sequence of characters enclosed in quotations marks ("Hello, World\n") is called a string.
  • Escape sequence\n indicates a newline.
  • Use \" to display quotes.
• return denotes the end of the main function. The zero value is a signal that the program ran successfully.

Errors (Syntax and Logic Errors)

• Syntax error or compile-time error:
  • Something violates the language rules.
  • Compiler finds the error.

    cot << "Hello, World!\n";
    cout << "Hello, World!\";

• Logic error or run-time error:
  • Program doesn't do what it's supposed to do.
  • Program author must test and find the error.

    cout << "Hell, World\n";

• Structuring programs so that an error in place does not trigger a disastrous response is called defensive programming.
• A program error is commonly called a bug; special software tools called debuggers help you locate bugs.
• Overflow and roundoff errors can occur when the result of a calculation is outside a computer's numeric range (i.e. either very big or very small).

The Compilation Process (Diagram)

The Compilation Process (Definitions)

• The C++ source code is your program.
• The compiler is a program that translate your C++ code into object code.
• Object code consists of machine instructions and information on how to load the program into memory.
• A linker program takes the object code from your program and the code from the various libraries and builds them into an executable file.
• Libraries contain the (already translated) code used by your program (such as iostream).

The Compilation Process (Edit - Compile - Debug Loop)

Algorithms

• A planning process must precede implementing a computer program.
• The computer needs a systematic approach for finding solutions: a series of steps that involves no guesswork.
• An algorithm is a solution technique (description of steps) that is unambiguous, executable, and terminating.
  • Unambiguous - no room for guesswork or creativity.
  • Executable - each step can be carried out in practice.
  • Terminating - the process will eventually come to an end.

Algorithms (Example)

You put $10,000 into a bank account that earns 5% interest per year. How many years does it take for the account balance to be double the original?

• Step 1: Start with the table
  

  After Year	Balance
  0	$10,000

• Step 2: Repeat steps 2a-2c while balance < $20,000
  • Step 2a. Add a new row to the table
  • Step 2b. In column 1 of the new row, put one more than the preceding year's value

  • Step 2c. In column 2, place the value of the preceding balance value, multiplied by 1.05.
    

• Step 3: Report the last number in the year column as the number of years required to double the investment