@ Monday 17th December 2007, 10:35 pm - Roger Gajraj

Hey guys, I promised to post some information relating to areas I feel you should know for you SEMESTER exams. A flu is trying to overcome me right now so I will not elaborate too much nor do fancy formatting.
Please study more in depth and do not just read this over.

A ‘Procedure’

A set of instructions which describe the steps to be followed in order to carry out an activity.

This can be for any activity:

eg recipe, assembly instructions etc

If it is written in a computer language it is called a program.

Describing Procedures Precisely

Flowcharts

Diagrams that include words which describe the individual tasks to be carried out and the decisions to be made in regard to carrying out tasks.

Pseudocode

Words that describe the individual tasks and special ‘keywords’ that describe the decisions to be made in regard to carrying out these tasks.

Top Down Programming with Stepwise Refinement

Designing a computer program by specifying as little of the details of how the job will be done at the early stages, but gradually defining tasks in more detail at later stages.

	Leave details as long as possible!
	Divide a job into it’s major components.
	Take each component and specify the major tasks involved.
	Break each task down into further tasks.
	This ‘refinement’ can be done as often as required.

Top-Down Design is used in all areas of design!

http://72.14.205.104/search?q=cache:iEO0v3TEpM8J:staffweb.itsligo.ie/staff/bmulligan/Lectures/CSFrench/French08.ppt+flowchart,+pseudocode,+top+down+design&hl=en&ct=clnk&cd=4&gl=gy&client=firefox-a

Dynamic memory allocation

In computer science, dynamic memory allocation is the allocation of memory storage for use in a computer program during the runtime of that program. It is a way of distributing ownership of limited memory resources among many pieces of data and code. Importantly, the amount of memory allocated is determined by the program at the time of allocation and need not be known in advance. A dynamic allocation exists until it is explicitly released, either by the programmer or by a garbage collector; this is notably different from automatic and static memory allocation, which require advance knowledge of the required amount of memory and have a fixed duration. It is said that an object so allocated has dynamic lifetime.

http://www-ee.eng.hawaii.edu/~tep/EE150/book/chap14/section2.1.2.html

http://www.technoplaza.net/programming/lesson6.php

Research and understand what really happens when a variable is created, and depending on WHERE in code it is created...find out how long it stays in memory.

Understand and know how:

pass-by-reference....e.g "void myFunction( int *ptrToNum );" ..and then .. called like: "myFunction( &someVariable );
pass-by-value............e.g "void myFunction( int number );" ..and then .. called like: "myFunction( someVariable );

Understand WHY files are used. Remember persistence of data?

FINALLY: Try to review your last test!

GOOD LUCK TO ALL!

@ Monday 22nd October 2007, 10:35 pm - Roger Gajraj

Sorry for not posting anything sooner. Meanwhile, here is a link to some online demo VIDEO tutorials I found on C.
http://ww.vtc.com/cd/C-Programming-tutorials.htm

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@ Wednesday 10th October 2007, 2:01 am - Roger Gajraj

understanding the for loop!

        int i;
        for( i = 0; i < 5; i++ ) // means initialize i to zero, check if i, at this time, is less than zero
     {                          // and if so THEN do code(...) in braces. Lastly, increment i by one(1) keep repeating
      /*...body of code*/       // whole process until i is not less than 5. Initialisation of i=0 is only done at first loop.
     }                          // Therefore, the body of code runs when i=0, i=1, i=2, i=3 and i=4, which is
                                    a total of five times!

N.B. You need to figure out how to change the numbers in the for construct to loop as many times as YOU want to

So, if you wanted the run the body of code 23 times, you needed to say: for( i=0; i<23; i++).

How many times do you think this loop will run for? : for( i=1; i<5; i++)

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@ Wednesday 10th October 2007, 1:48 am - Roger Gajraj

CONTROL CONSTRUCTS - loops
loops are used to rerun some part of code.

C contains a number of looping constructs, such as the "while" loop:

/* while.c */ #include <stdio.h> void main() { int test = 10; while( test > 0 ) { printf( "test = %d\n", test ); test = test - 2; } }

If "test" starts with an initial value less than or equal to 0 the "while" loop will not execute even once. There is a variant, "do", that will always execute at least once:

/* do.c */ #include <stdio.h> void main() { int test = 10; do { printf( "test = %d\n", test ); test = test - 2; } while( test > 0 ); }

The most common looping construct is the "for" loop, which creates a loop much like the "while" loop but in a more compact form:

/* for.c */ #include <stdio.h> void main() { int test; for( test = 10; test > 0; test = test - 2 ) { printf( "test = %d\n", test ); } }

Notice that with all these loops, the initial loop statement does not end with a ";". If a ";" was placed at the end of the "for" statement above, the "for" statement would execute to completion, but not run any of the statements in the body of the loop.

The "for" loop has the syntax:

for( <initialization>; <operating test>; <modifying expression> )

So:   for( i=0; i<5; i++) // means initialize i to zero, check if i, at this time, is less than zero
     {                     // and if so THEN do code(...) in braces. Lastly, increment i by one(1) keep repeating
      /*...body of code*/ // whole process until i is not less than 5. i=0 is only one at first loop.
     }                     // Therefore, the body of code runs when i=0, i=1, i=2, i=3 and i=4, which is a total of five times

All the elements in parentheses are optional. A "for" loop could be run indefinitely with:

for( ; ; ) { ... }

-- although using an indefinite "while" is cleaner:

while( 1 ) { ... }

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@ Wednesday 10th October 2007, 1:23 am - Roger Gajraj

CONTROL CONSTRUCTS - decision making

C also contains decision-making statements, such as "if":

/* if.c */ #include <stdio.h> #define MISSILE 1 void fire( int weapon ) void main() { fire( MISSILE ); } void fire( int weapon ) //function to fire. Takes in one integer value { if( weapon == MISSILE ) { printf( "Fired missile!\n" ); } if( weapon != MISSILE ) { printf( "Unknown weapon!\n"); } }

This example can be more easily implemented using an "else" clause:

/* ifelse.c */ void fire( int weapon ) { if( weapon == MISSILE ) { printf( "Fired missile!\n" ); } else { printf( "Unknown weapon!\n"); } }

Since there is only one statement in each clause the curly brackets aren't really necessary. This example would work just as well:

void fire( int weapon ) { if( weapon == MISSILE ) printf( "Fired missile!\n" ); else printf( "Unknown weapon!\n" ); }

However, the brackets make the structure more obvious and prevent errors if you add statements to the conditional clauses. The compiler doesn't care one way or another, it generates the same code.

There is no "elseif" keyword, but "if" statements can be nested by the following code.

NOTE TO STUDENTS: (not "elseif") but "else if" is valid because 'if' is nested in 'else' since if comes directly after. Notice that "else if" was used in class.

/* nestif.c */ #include <stdio.h> #define MISSILE 1 #define LASER 2 void fire( int weapon ) void main() { fire( LASER ); } void fire( int weapon ) { if( weapon == MISSILE ) { printf( "Fired missile!\n" ); } else { if( weapon == LASER ) { printf( "Fired laser!\n" ); } else { printf( "Unknown weapon!\n"); } } }

This is somewhat clumsy. The "switch" statement does a cleaner job:

/* switch.c */ void fire( int weapon ) { switch( weapon ) { case MISSILE: printf( "Fired missile!\n" ); break; case LASER: printf( "Fired laser!\n" ); break; default: printf( "Unknown weapon!\n"); break; } }

The "switch" statement tests the value of a single variable; unlike the "if" statement, it can't test multiple variables. The optional "default" clause is used to handle conditions not covered by the other cases.

Each clause ends in a "break", which causes execution to break out of the "switch". Leaving out a "break" can be another subtle error in a C program, since if it isn't there, execution flows right through to the next clause. However, this can be used to advantage. Suppose in our example the routine can also be asked to fire a ROCKET, which is the same as a MISSILE:

void fire( int weapon ) { switch( weapon ) { case ROCKET: case MISSILE: printf( "Fired missile!\n" ); break; case LASER: printf( "Fired laser!\n" ); break; default: printf( "Unknown weapon!\n"); break; } }

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@ Wednesday 10th October 2007, 12:58 am - Roger Gajraj

This is to supplement the notes you have on how code is compiled into an executable:

C compilation is a multi-pass process. To create a program, a C compiler system performs the following steps:

	It runs the source file text through a "C preprocessor". All this does is perform various text manipulations on the source file, such as "macro expansion", "constant expansion", "file inclusion", and "conditional compilation", which are also explained later. The output of the preprocessor is a second-level source file for actual compilation. You can think of the C preprocessor as a sort of specialized automatic "text editor".
	Next, it runs the second-level source file through the compiler proper, which actually converts the source code statements into their binary equivalents. That is, it creates an "object file" from the source file.
	The object file still cannot be executed, however. If it uses C library functions, such as "printf()" in the example above, the binary code for the library functions has to be merged, or "linked", with the program object file. Furthermore, some addressing information needs to be linked to the object file so it can actually be loaded and run on the target system. These linking tasks are performed by a "linker", which takes one or more object files and links them to binary library files to create an "executable" file that can actually be run.

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@ Tuesday 9th October 2007, 10:24 pm - Roger Gajraj

I found this slideshow online. If you are interested you can take a look.

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@ Monday 8th October 2007, 2:00 pm - Roger Gajraj

The following is working code for the tax program:

#include <stdio.h> // includes
#include <stdlib.h>

float tax(int gsal); // function prototype

int main(int argc, char *argv[]) // main function
{
    float taxes; // container to hold tax
    int sal; // container to hold salary

    printf("enter your gross Salary:"); // ask user to enter salary
    scanf("%d", &sal); // user input is copied to variable "sal"
    taxes = tax(sal); // the "tax" function is called to compute and return float value by passing "sal" to it (sal = user input).
                       // So return value is copied to "taxes".

    printf("your gross salary is %d \n", sal); // print salary
    printf("your total taxes is %f\n", taxes); // print tax
    printf("Net salary is %f\n", (float)sal-taxes); // print net salary

    system("PAUSE"); // pauses screen
    return 0; // exit main function and return 0
}

float tax(int gsal) // function to compute tax where it takes in an "int" value
{
    float taxR = 0.0; // container to hold tax value

    if (gsal > 25000 && gsal <= 30000) // if salary is more than 25000 yet less than or equal to 30000 then do next line only
        taxR = 0.20 * gsal - 25000; // tax is calculated and put in "taxR"

    else if (gsal>30000) // if previous if statement was false, then check if salary is more than 30000. If so, then do next line only
        taxR = (0.20 * 5000) + (gsal - 30000) * 0.33; // tax is calculated and put in "taxR"

    return taxR; // returns "taxR" ( actual tax calculated) to WHERE THE FUNCTION WAS CALLED!
}

/////////////////////////////////////////////////////////////////////////////////END OF CODE/////////////////////////////////////////////////////////////////////////////////////

NOTES:

Please email any questions to r_gajraj@hotmail.com.

This is the first post I am making and I will make more posts tonight. Please check back then.

In the meanwhile, http://www.howstuffworks.com/c.htm has a good tutorial on C

HINTS:

Please try to revise how the "compiler" works with all it's steps. (first set of notes)

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