programming experience let’s get a feel for everyones’ programming experience. query languages...

Programming experience

Let’s get a feel for everyones’ programming experience.Query languages known

Query knowledge of looping constructs

Query knowledge of conditional statements

Query knowledge of subroutines

S1-1A.Honey (Oct 2003)

Program categorization

There are several ways to categorize programming languages, however the one I wish to discuss is relevant to scripting, interpreting, and compiling.

Can anyone explain the differences and give examples?


Scripted language

A scripting language is used to coordinate and combine components that are written in some other language and cannot usually itself be used for writing those components. The programs you create are read by another program which then executes the statements you created. (Perl, Tcl/Tk, HTML, XML)


Scripted language

A scripting language is used to coordinate and combine components that are written in some other language and cannot usually itself be used for writing those components. The programs you create are read by another program which then executes the statements you created. (Perl, Tcl/Tk, HTML, XML)

Interpreted language

An interpreter is a computer program that executes other programs. Most interpreted languages use an intermediate representation, typically called bytecode, which is then executed by a bytecode interpreter. The interpreter would most likely be written in a compiled language. There are more-or-less two programs involved, one to convert to bytecode and one to run that bytecode. (Basic, Java, Python)


Compiled language

A compiler does not execute its input program (the source code) but translates it into executable machine code (also called object code) which is output to a file for later execution. The ‘executable program’ consists of a set of CPU instructions that run directly on the processor chip and, therefore the compiler must translate the source code into instructions for a particular CPU. Hence, a program written for a Pentium PC (Intel) will not run on a Mac (PowerPC)! (C, Fortran, Cobol)

An interpreter or script program may run on both. Those types of programs are what is called platform independent.

Which is fastest?

So how many programming languages are there?


ABC Blue ConstraintABEL C CurlAda C++ DADL C-sharp DatabaseAleph Caml DataflowAlgol 60 Cecil DeclarativeAlgol 68 CHILL DelphiAPL Clarion Directories AppleScript Clean DOS batchASP Clipper DylanAssembly CLU EAwk Cobol EiffelBASIC CobolScript ElastiCBefunge Cocoa ErlangBETA Compiled EuphoriaBigwig Component Pascal ForthBistro Concurrent Fortran


FP Interpreted MLFrontier Java Modula-2Functional JavaScript Modula-3Garbage Collected LabVIEW MotoGoedel Lagoona MultiparadigmHardware Description Leda MumpsHaskell Limbo NETHistory Lisp ObfuscatedHTML Logic-based Object-OrientedHTMLScript Logo Objective-CHyperCard Lua ObliqICI m4 OccamIcon Markup Open sourceIDL MATLAB OzImperative Mercury ParallelIntercal Miranda PascalInterface Miva Perl


PHP Rexx SQLPike Rigal SqueakPL RPG T3XPL-SQL Ruby Tcl-TkPliant S-Lang TempoPOP-11 SAS TOMPostscript Sather TRACPowerBuilder Scheme TuringProcedural Scripting UMLPrograph Self VBAProlog SETL VBScriptProteus SGML VerilogPrototype-based Simula VHDLPython Sisal VisualREBOL Smalltalk Visual DialogScriptReflective snobol Visual FoxProRegular Expressions Specification Water


Wirth XML XOTcl YAFL Yorick Z

The above was NOT an exhaustive list!


Lcc-win32

Why lcc-win32 rather than IC4 for these sessions?

Interactive C is truly interactive requiring that your computer be connected to a robot controller. If not then it becomes very tedious to write a program, as every time you press enter an attempt is made to send the statement to the controller and if it is not there then a delay of many seconds will occur.

Also the lcc-win32 has a 300+ page tutorial, which will become very useful when you start training your team members in the C programming language.

I intend to devote one of the later sessions to IC4. If for some reason this does not occur then the botBall workshop in Honolulu will be sufficient.


Learning a programming language

So what does one need to learn in order to become proficient in a programming language?




The Syntax which is the arrangement of words and symbols to create a working statement structure.





The acceptable words of the language.






The acceptable punctuation.







The structure of a program.








Looping constructs.








Looping constructs.

Conditional statements and expressions.








Looping constructs.


How to create subroutines or there equivalent.








Looping constructs.


How to create subroutines or there equivalent.

How to declare and define variables and subroutinesS1-19A.Honey (Oct 2003)


When learning a programming language the syntax has to be correct or, either an error will be generated (especially true for a compiled language) or the program will not behave as expected and/or the program will ‘crash’!


How is a C program organized?Tutorial pdf page 13, doc page 1

A C program consists of one or more source files called modules.

So why would you break a program into multiple modules?


C modules

A large complex program ‘needs’ to be broken into modules. Not only does this allow a team of programmers to work more-or-less independently, on various pieces of a large program, but also it allows the program to be more readily understood and maintainable.

In addition, with judicious modularization, a module may prove to be useful in another program, thereby, reducing the amount of new code that is written for each new program.

Of course if multiple programmers are working on different pieces of a program then they must agree, in advance, upon the inputs and outputs (parameters) to each smaller piece of the program (functions).


C functions

In C, the equivalent of a subroutine is called a function.

A C program may consist of an almost unlimited number of functions. However, at least one function must exist and it must be called ‘main’.

Typically, if you find that there is a set of statements that you need to use several times, in various places in your program, then you would probably create a function for that code. Or perhaps to simply make the program more easily read/understood. Or if that code maybe useful in another program.

A C function is typically a small piece of code that: has zero or more parameters; has zero or more declarations; contains zero or more program statements, which accomplish a desired task; and may or may not return a result.


C function parameters

For now we will defer a discussion of function parameters. Suffice it to say the function parameters allow data to be passed in to and/or out of a function, such that the statements of that function can manipulate the data.

We will return to this topic when the need arises.


C function declarations

Declarations are the means by which we create variables and provide their specifications to the compiler.

A variable allows us to ‘tell’ the compiler information about the data we want to manipulate or examine, within the statements of the program.

So what is a variable?


C function declarations

Declarations are the means by which we create variables and provide their specifications to the compiler.

A variable allows us to ‘tell’ the compiler information about the data we want to manipulate or examine, within the statements of the program.

So what is a variable?

A variable is essentially the ‘name’ of a data value that is stored in a particular memory location. It is the compiler and linker which determine the exact memory location used for a given variable.


C variables

Lets backup a little. Even though you may not know how to do this yet, assume you have created and compiled a C program. Where is that program?


C variables


Right it is on a disk drive.

For a compiled C program what is on the disk drive?


C variables





source code, object code, and executable program!

Now you ‘run’ the program. What happens to the program?

C variables







Right it is loaded into the computer’s memory.

C variables







Right it is loaded into the computer’s memory.

So what is memory?

C variables

Computer memory can be visualized as a large set of switches that can be either on or off (in actual fact they are the equivalent of microscopic transistors which do function like switches). If we think of each switch as being numbered then the numbers are analogous to the addresses of the memory locations. Each memory address refers to…


C variables


the equivalent of how many switches?


C variables


the equivalent of how many switches?

think win32


C variables

Computer memory can be visualized as a large set of switches that can be either on or off (in actual fact they are the equivalent of microscopic transistors which do function like switches). If we think of each switch as being numbered then the numbers are analogous to the addresses of the memory locations. Each memory address refers to 32 switches as that is the data width on the current generation of IBM type PCs.

So why do we care about the data width?


C variables

Computer memory can be visualized as a large set of switches that can be either on or off (in actual fact they are the equivalent of microscopic transistors which do function like switches). If we think of each switch as being numbered then the numbers are analogous to the addresses of the memory locations. Each memory address refers to 32 switches as that is the data width on the current generation of IBM type PCs.

So why do we care about the data width?

The speed of memory is typically much slower than the processor so, if you can get more information in a single memory read or write, then your the entire system becomes more efficient. And, you can update your video card faster


C variables

As we will eventually see, a C program may contain variables of practically any type imaginable. However, there are only a few basic variable types, from which all other variables are derived.

Within this session we will only address two of those basic types, namely, integer and floating-point variables.

So why do we need to tell the compiler that a given variable is of a specific type?


C variables

As we will eventually see, a C program may contain variables of practically any type imaginable. However, there are only a few basic variable types, from which all other variables are derived.

Within this session we will only address two of those basic types, namely, integer and floating-point variables.

So why do we need to tell the compiler that a given variable is of a specific type?

It basically comes down to the representation of integers and float-point values in memory. They are NOT the same!

The compiler MUST know the type of the variable so it correctly interprets the data, in a given memory location.


Simple C program S1_pgm1

Lets create a simple program.

I assume everybody has downloaded and installed lcc-wn32.

You should have an icon on your desktop for wedit

If not then try start->Programs->lcc-win32

If not then open the ‘bin’ folder wherever you installed LCC and the executable should be there.


Simple C program

The program you created calls the function printf but where did that function come from? You didn’t create it.


Simple C program


There are hundreds of functions in C that exist in either other source files or as object modules (the output from the compiler). A programmer may use those functions. It is the job of the linker to find those functions and include them in the compiled program. So how does the linker know which functions to include?


Simple C program


There are hundreds of functions in C that exist in either other source files or as object modules (the output from the compiler). A programmer may use those functions. It is the job of the linker to find those functions and include them in the compiled program. So how does the linker know which functions to include?

That word ‘include’ was the clue as there was a preprocessor statement ‘#include <stdio.h>’ at the top of your program. That was a directive to include the module for standard input and output. Within the .h file there is information pertaining to the functions in the module. This also allows the compiler to determine if you have the parameters to the functions correct.



So modify your program by adding another printf statement but without any arguments.

Then recompile the program.

What happens?


Simple C program



What happens?

You get a compiler error telling you that you used the printf function incorrectly. The compiler knows what to expect as there is information in stdio.h regarding the functions’ parameters.


Simple C program



What happens?


It is the preprocessor which responds to the statements that are preceded with ‘#’. For the include directive, the preprocessor finds the .h file and feeds it into the compiler. The compiler then uses that information while parsing/translating the program.


Simple C program



What happens?


It is the preprocessor which responds to the statements that are preceded with ‘#’. For the include directive, the preprocessor finds the .h file and feeds it into the compiler. The compiler then uses that information while parsing/translating the program.

Subsequently, the linker will use that information to find the actual function code. S1-46A.Honey (Oct 2003)


So lets modify your program again to return to the subject of variables.

Remove the faulty printf statement and add declarations for an integer variable and a floating-point variable.

Anybody know what is needed?


Simple C program




int ivar;

float fvar;


Simple C program




int ivar;

float fvar;

The declarations tell the compiler that there are two variables that may be used in the program and, that those variables have certain storage and representation requirements. The compiler does not necessarily allocate storage for variables until it encounters program statements which use them.



Now we will modify the program to define the variables that we declared. For now we will just assign some constants.

ivar = 1111.6;

fvar = 1111.6;

What do you think happens when these statements are compiled?


Simple C program


ivar = 1111.6;

fvar = 1111.6;

What do you think happens when these statements are compiled? The compile finds memory locations for the variables and writes the values into those locations.

What is stored in ivar?


Simple C program


ivar = 1111.6;

fvar = 1111.6;

What do you think happens when these statements are compiled? The compile finds memory locations for the variables and writes the values into those locations.

What is stored in ivar? Remember we told the compiler that ivar was an integer variable.



Let’s modify the program to display the values stored in the variables.

Can you explain the result?


Simple C program

Let’s modify the program to display the values stored in the variables.

Can you explain the result?

Because we told the compiler that ivar was an integer it only reserved memory for an integer and it only wrote the integer part of the value into that memory, truncation occurred!


C variables

I beseech you to NOT use single letter variable names!

Why not?


C variables

I beseech you to NOT use single letter variable names!

Why not?

If you have to search through your program for a variable and it is a single letter then it becomes very tedious.


C variables

So, when we define a variable, the compiler finds some memory location for the variable and notes the name of the variable along with the address of that memory. Then, when the variable is used in the program, the compiler causes the contents of that memory to be either written or readback. The amount of memory needed and how it is used is completely determined by the variables type.


More C program structure

As you have probably surmised by now, C programming statements appear to terminate with ‘;’ This is true in most cases.


More C program structure

As you have probably surmised by now, C programming statements appear to terminate with ‘;’ This is true in most cases.

Blocks of code (programmer generated groups of statements) are typically enclosed in braces ‘{…}’ This will become more evident when we learn about conditional statements and looping constructs. The braces are also used to delineated the beginnings and endings of functions.

The arguments to function calls (e.g. printf) must be enclosed in parentheses.


C variables S1_pgm6

Let’s now add statements to use the variables.

ivar = ivar * fvar;

fvar = ivar * fvar;

What do you think will be the result in each case?


C variables S1_pgm7

Let’s now add statements to use the variables.

ivar = ivar * fvar;

fvar = ivar * fvar;

What do you think will be the result in each case?

Add in printf statements to see if you are correct.


C variables S1_pgm8

Let’s delete most of the program and experiment with user entered variable values.

The first method is to provide the value when the program starts. These are called ‘command line arguments’.

The compiler always supplies at least one argument to the main function. Add in a printf to see what it is.


C variables S1_pgm9

Let’s delete most of the program and experiment with user entered variable values.

The first method is to provide the value when the program starts. These are called ‘command line arguments’.

The compiler always supplies at least one argument to the main function. Add in a printf to see what it is.

Now add statements to display two more arguments. We will enter the arguments from the configuration window. On the project pulldown, select configuration and then click on the Debugger tab. Enter two space separated strings.


C variables S1_pgm10

The second method for getting user values is to query for keyboard input. So modify your program to request values using the scanf function.




There is a new syntactical item in what we have done. That is, the ampersands in front of the variables that were the arguments to the scanf function.




There is a new syntactical item in what we have done. That is, the ampersands in front of the variables that were the arguments to the scanf function.

The ‘&’ tells the compiler to pass the address of the variable, which is actually the address of the memory location. This is called passing by reference. Why do you think this is necessary?


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