KJE431-Computing and Simulation,
Supplementary Notes for BSc EE-UiTM Shah Alam (now UiTM) Students

5.1 Enumerated data types in C

The enumerated type lets programmers define symbolic names to represent integer constants, to enhance program readability.

Example : Enumerated data type declaration 

enum colors { red,blue,green,black };
enum colors color; /* for C++ enum keyword is optional in variable declaration*/ 

In this case red will have a value of 0, blue will have a value of 1 and etc.

5.2 Pointers

A pointer is a variable that hold and address of some data, rather than the data itself. The use of pointer is usually closely related to manipulating (assigning or changing) the elements of and array of data. Pointer are used primarily for three purposes:

Two special pointer operators are required to effectively manipulate pointers:

. Pointer in C is easy as long as one remembers one simple rule of thumb that is pointer can only be assigned to a pointer itself ( of the same kind, or of type void) and to and address of a variable.

Example :Pointer in action ... 


int main()
{ 
 int i,*ptr; i=7; ptr = &i; /* ptr points to i */ 
 printf ("\n%d",i);/* display 7 */ 
 printf ("\n %d",*ptr); /* display 7 */ 
 *ptr =11; /* i and *ptr = 11 */ 
 printf ("\n %d %d",*ptr,i); 
 return 0; 
} 

Example: String and pointers... 

char *name; char *name1="Ali"; // initialization during declaration 
strcpy (name,"fadzil"); /* assignment name="fadzil" is not proper*/                                                         

Unlike other programming language, assignment involving string quite tricky at run time. Simply assigning for example, name="fadzil" is not acceptable. A standard C function strcpy must be used (located in string.h). As an alternative one can use a one to one assignment. It is interesting to note that C automatically appends '\0' at the end of every string.

Example: One to one assignment

char *p;
char *name="maliki";
char *copyname;

p=name;
while (*p!='\0')
 {
  copyname[i]=*p;
  p++;
  i++;
 }

5.3 Structures

The general form declaration of an N element structure is as follows: struct tag_name { type1 element_name1; type2 element_name2; . . typeN element_nameN; } variable_name

Example: Example of structure 

struct students { char *name; int age; } 
struct students Group1; /* In C++ the keyword struct is unnecessary*/ 
struct students *Grp; 
... 
strcpy(Group1.name,"Mohd Asri");
Group1.age=26; 
Grp=&Group1; /* Necessary to initialize the string */
strcpy(Grp->name,"Mohd Asri"); /* accessing the element using pointer */ 
Grp->age=26; 

5.4 Array

The general form declaration is as follows: datatype var_name [] ;

Example: Example of array declaration 

struct students Group1[10]; /* declare array of structure Group1 */ 
int days[7]={1,2,3,4,5,6,7};
char name1[]; /* declare array of char i.e string */ 
char *name2 ;/* also declare array of char i.e string */ 
char name3[3]; /* declaring array of char of 3 char long */ 
int number [3][3] /* array 3 x 3, 2 dimension */

Example: Accessing array using subscript & pointer; 

int data[2]= {100,300}
int moredata[2]={100,300}; 
... 
int *p1,*p2,*p3; 
p1=p2=&data; /* notice the rule of thumb */
p3=moredata;     /* ditto */
printf ("%d %d %d\n",(*p1)++,*(++p2),*++p3); 
printf ("%d %d %d\n",*p1,*p2,*p3); 
printf ("%d %d ",data[1],data[2]);
... 

As an exercise predict the output of the above program !!!.

6.0 Operators

6.1 Usage of bit operation:

-Turning one bit on and others off.
Flag = 0xFF;// 11111111
Mask = 0x01;//00000001
Flag & Mask will set bit 0 to 1 and set all other bit to 0.

-Turning one bit off and leaving others unchanged
Flag = 0xFF; // 11111111
Mask=0x08; // 00001000
Flag & ~Mask will turn bit 3 off and leaving other bit unchanged.

-Toggling bits - turn it on if it is off, and turn it off if it is on
Flag = 0xFF;// 11111111
Mask=0x08;// 00001000
Flag ^ Mask will turn bit 3 off if it is on. To turn it on if it is off, perform the exclusive or operation again.

-Left shift <<
Flag = 0xAF; // 10101111
Flag<< 2 will left shift Flag to 10111100

- Right shift >>
Flag= 0xAF; // 10101111
Flag >> 3 will right shift Flag to 00010101

-Testing for bits
~ Flag = 0x1F; //10101111
if (Flag & 0x10) is true then bit 4 is set.

7.0 Control Statements & Looping

7.1 Conditional Execution:if ..else

The if statement has the following generic format:

 
   if (test condition) 
        statement1; 
    else statement2; 
   

When more than one statement needs to be executed if a particular value is true, a compound statement is used. A compound statement consists of a left brace ({) , some number of statements (each ending with semicolon), and a right brace ({).

Example: Using the if statement
  if (result > 0) 
    { /* positive outputs */ 
     if (result > delta) out= 1; /* assignment statement */ 
       else out = 0; 
    } else 
    { /* other that positive outputs */ 
      if (result <-delta) out = -2; 
        else out = -1; 
    } 
Example: Confusing if statement 
   return (a>b) ? a:b; /* this is the most confusing to beginner!!! */ 
   if ( a > b ) /* this is its equivalent statement that less confusing*/
     return a; 
   else 
     return b; 

7.2 The case & switch statement

The basic form of the switch statement is as follows:

 
 switch (integer expression)
   { 
    case constant1: 
         statement; 
    break; 
    case constant2: 
         statement; 
    break; ....................
    default: 
    statement; 
   }
 

Example: Case statement in action 

      char c; 
      ... 
      switch(c) 
       { 
        case 'a': 
                 printf ("a \n"); 
                 i++; 
                 break; 
        case 'b':printf("b\n"); 
                 i++; 
                 break; 
        case '@':DONE=TRUE; 
                 break; 
        default: i=0;
                 break; 
       } 

7.3 while loop

If the test expression is true, the execution of the program goes inside the while loop. The while loop repeats the statements until the test expression become false. The basic form of the while loop is:

     while (test expression) 
       { statement; 
       } /* braces are necessary only for compound statement */ 


Example:While loop in action 
     int main () 
       { int n = 0; 
         while (n < 3) 
          { 
            printf ("\n Hoi ... Maliki... error %c \n",0x7);
            n++; 
          } 
         printf ("Says who \n "); 
       } 

7.4 do while loop

The do while loop also works as the while loop. In the do loop the statement inside the do while loop will be executed at least once eventhough the test expression is false. The basic form of the do while loop is:

 
      do 
       { statement; 
       } while (test expression) 

Example:The do while loop 

      int number; 
        ... 
      do 
        scanf("%d",&number);
      while (number != 20);
 

7.5 for loop

The for loop combines an initialization statement, an end condition statement may be a single statement , a compound statement or just a semicolon (a null statement). The basic form of the for loop is:

     for (initialize; test condition;end update) 
       { 
        statement; 
        statement;
        }  /* braces is unnecessary for non compound statement */ 

Example: The for loop 
       ... 
       int main () 
        { int counter; 
          for (counter = 1; count<= 10;count++) 
            { 
             printf ("\nI love ITM \n"); 
             printf ("Where I used to study\n"); 
            } 
        } 

8.0 Functions

All C/C++ program consist of one or more function. Even the program executed first is a function called main( ).A C/C++ function may or may not return a value.Any function can call any other function, or called by any other function.C/C++ always passes functions "by value" not "by reference".To pass variable "by reference" the C/C++ programmer must specify the function argument as a pointer.

8.1 Defining and declaring functions

The general format is as follows:

      datatype functionname (formal argument) 
        { 
          statement;
        } 

The data type determines the type of value the function returns, not the type of arguments. If no data type is specified, the function is assumed to return an int. If a function does not return a value, it should be declared with the type void.

Example:Function returning an integer value 
  #include 
  #include 
  int x,y,z; 
  int larger_of(int a, int b); 
  int main() /* the main () function returns type int */ 
    { 
     puts("enter two different integer values: ");       
     scanf("%d%d", &x,&y); // note &address of
     z = larger_of(x,y); 
     printf("\n The larger value is %d. ", z); } 
     return 0;
    }

 int larger_of(int a, int b) /* the larger_of function returns type int */ 
    { 
     if ( a > b ) 
      return a; 
     else
      return b; 
    } 

8.2 Storage Class, Privacy and Scope.

In addition to type, variable and functions have a property called storage class. There are three storage classes with three storage class designators: auto for automatic variables stored on the stack,extern for external variables stored outside the current module, static for variables known only in the current module.

Auto variables can only be declared within a function, are created when the function is invoked and are lost when the function is exited. Auto variable are known only to the function in which they are declared and do not retain their value from one invocation of a function to another.Because auto variable are store on a stack, a function that use only auto variable can call itself recursively. The auto keyword is rarely used in C programs since variable declared within function default to the auto storage class. Extern variable have broadest scope. They are known to all function in a module and are even known outside of the module in which they are declared. Extern variables are stored in their own separate data area and must declared outside of any function. Static variables differ from extern variables only in scope. Static variables declared outside of a function in one module is known only to the functions in that module. A static variables declared inside a function is known only to the function in which it is declared.

8.3 Passing parameter to function by refence

By default C passes parameter by value. To pass parameter by reference pointer must be used.

Example:The swap program 

void swap (int *x1,*x2) 
 { 
   int temp; 
   temp = *x1; 
   *x1=*x2;
   *x2=temp; 
  } 
  ... 
  int main () 
   {  
    int p=1,q=2; 
    printf ("%d %d",p,q);/* print 1 2 */ 
    swap (&p,&q); /* Note the ampersand &, address of */ 
    printf ("%d %d",p,q); /* print 2 1 */ return 0; 
    return 0;
   } 

9.0 C Macro

Some function can be implemented using macros for speed. Function call will use up code segment stack, whereas macro does not. The macro call will be replaced by the actual codes and gets appended to the final executable file. The rule of thumb to use macro is when the function called involved some formulae. Remember, all macros can be converted to function and not all function can be converted to macros.

Example: using ordinary function 
float square (float x) 
  { 
   return x*x; 
  } 

Example: using Macro 
  #define SQUARE (x) (x)*(x) // brackets are neccessary to avoid side effect          
  #define FORMULA (y) (y)*(sin(y)) 10.0

10.0 RS232 Interfacing with C for MS DOS environment Turbo C++

Among the featuresof C that surpasses other language are:

The example given below is the most useful when programming the serial port. Feel free to copy it,for educational use, but please dont claim credit.

Example: Acessing Port Using Turbo C++ ( Library) 
/* Only works with COM 1, to use COM2 or etc the address must be specified in */ /* each parts of the routines, i.e COM2 0x2F8 */
/* Part of the codes are adopted from The Book DOS Programmers Reference */
#include <stdio.h>
#include <bios.h>
#include <dos.h>
#include <conio.h>
#include <string.h>
#include <process.h>
#define COM2 1 
#define COM1 0 
#define DATA_READY 0x100 

void port_init (int port,char code ); 
void send_port (int port,char c); 
void send_port_direct (int port,char c); 
int receive_port(int port);
int receive_port_direct (int port); 
int check_status (int port ); // Initializing the com port 

// Tested OK 
void port_init (int port,char code ) 
 { union REGS r; 
   r.x.dx=port; 
   r.h.ah=0; 
   r.h.al=code; 
   int86(0x14,&r,&r);
  } 

// send character to port 
// Tested OK.. Meant to be used for slower access & response equipment 
void send_port (int port,char c) 
 { union REGS r; 
   r.x.dx=port; 
   r.h.ah=1; 
   r.h.al=c; int86(0x14,&r,&r);
   if (r.h.ah & 0x80) 
     { 
       printf ("Error sending %c to the serial port \n",c); 
       if (kbhit()) exit(1); 
     } 
 } 

// Direct access to the port level
void send_port_direct (int port,char c) 
 { #define LSR 5 
   #define THR 0 
   #define THRRDY 0x20 
   int address; 
   register int cnt; 
   
   if (port==COM1) 
     address=0x3F8;
   if (port==COM2)
     address=0x2F8;
   cnt=0; 
   while (!(inportb(address+LSR) & THRRDY) && cnt <10000) 
   cnt++; 
   if (cnt>=10000) 
    { 
     printf ("Error sending %c to the serial port\n",c); 
     exit (0); 
    } 
   outportb(address+THR,c); 
 } 

// Check status of the serial port 
int check_status (int port ) 
 { union REGS r;
   r.x.dx=port; 
   r.h.ah=3; 
   int86(0x14,&r,&r); 
   return r.x.ax; 
 } 

// Receive from the serial port 
int receive_port (int port) 
 { union REGS r; 
  while (!check_status(port)& 0xFF) 
   if (kbhit()) 
     { 
      getch(); 
      exit (1); 
     } 
  r.x.dx=port;
  r.h.ah=2; 
  int86(0x14,&r,&r); 
  if (r.h.ah & 0x80) 
   { 
     printf ("Error receiving character from the port \n"); 
     if (kbhit()) 
       exit(1); 
   } 
 return r.h.al; 
 }

 // Receive directly from the specific address 
int receive_port_direct(int port) 
{ #define RDR 0 
  #define MASK 0x7F 
  int address; 
 
  if (port==COM1)
    address=0x3F8; 
  if (port==COM2)
    address-0x2F8;
  
  return (inportb(address+RDR)&MASK); 
 } 

/* Demonstrates the most basic mouse function */
#include <conio.h>
#include <stdio.h>
#include <dos.h>// prototypes 
int initialize_mouse(); 
void reset_mouse (); 
void show_mouse_pointer (); 
void hide_mouse_pointer(); 
void get_mouse_position (int *x, int *y, int *mousebutton); 
void show_mouse_coordinate(); 
void clear_mouse_coordinate (); 

union REGS iReg, oReg; 
struct SREGS segregs; 
int c, numbuttons, oldmouse, mousebutton, movx, movy; float mouseversion;
int Quit; 
int x,y,Buttons,OldX,OldY; 

void main () 
 { _setcursortype (_NOCURSOR);
   clrscr(); 
   gotoxy (15,5);cputs ("Mouse Movement Demonstration Program");
   gotoxy (15,6);cputs ("Written For PDRM staff by Kamal Zamli");
   show_mouse_pointer();                            
   gotoxy(18,9);puts("*****************************************");
   gotoxy (18,10);puts("Click Here to Quit");      
   gotoxy(18,11);puts("**************************************");
   Quit=0; 
   OldX=-1; 
   OldY=-1; 
   while (!Quit) 
    { 
     get_mouse_position(&x,&y,&Buttons);
     if ((OldX != x) || (OldY != y)) 
       { 
        clear_mouse_coordinate(); 
        show_mouse_coordinate();
        OldX=x; 
        OldY=y; 
       } 
    if (((x>=15) & (x<=35)) & ((y==9)) & (Buttons==1)) 
      { 
        Quit=1; 
      }
 } 
 hide_mouse_pointer(); 
 reset_mouse(); 
 clrscr();
 _setcursortype (_NORMALCURSOR); 
} 

void clear_mouse_coordinate() 
 { 
  hide_mouse_pointer();
  gotoxy (25,1); puts (" "); 
  gotoxy (25,2); puts (" ");
  show_mouse_pointer(); 
 } 

void show_mouse_coordinate () 
 { 
  char xstring[10],ystring[10];
  hide_mouse_pointer(); 
  sprintf (xstring,"x = %d",x); 
  sprintf (ystring,"y= %d",y); 
  gotoxy (25,1);puts (xstring); 
  gotoxy (25,2);puts (ystring);
  show_mouse_pointer(); 
 } 

int initialize_mouse () 
 { 
  iReg.x.ax = 0; 
  int86(0x33, &iReg, &oReg); 
  if (oReg.x.ax == 0xFFFF) 
   return (oReg.x.bx);
  else return 0; 
} 

void reset_mouse () 
 { 
  iReg.x.ax = 0; 
  int86 (0x33, &iReg,&oReg); 
 } 

void show_mouse_pointer () 
 { 
  iReg.x.ax = 1; 
  int86 (0x33,&iReg, &oReg); 
 } 

void hide_mouse_pointer () 
 { 
  iReg.x.ax = 2; 
  int86(0x33, &iReg, &oReg); 

 }

 void get_mouse_position (int *x, int *y,int *mousebutton) 
{ 
 iReg.x.ax = 3; 
 int86 (0x33, &iReg, &oReg);
 *x = oReg.x.cx / 8; 
 *y = oReg.x.dx / 8; 
 *mousebutton = oReg.x.bx; 
 } 

12.0 C Common Library (string manipulation & File I/O using C)

Example: using common string functions 
#include <stdio.h>
#include <string.h>
int main() 
  { 
   char *string; 
   strcpy(string,"hello");/*  string="hello" is not allowed */     
   printf("%s\n", string); 
   strcat (string,"...dude"); /* append .. dude to string */ 
   strrchr (string,'e'); /* search for the char e */ 
   strstr (string,"dud"); /* search for a sub string in a string */ 
   strlwr (string); /* convert to lower case */ 
   strupr (string);/* convert to upper case */ 
   strset (string,'x'); /* set string to just x's */ 
   return 0; 
  } 

Example: Using malloc () and gets () to allocate storage space of string #include <stdio.h>
#include <alloc.h>
#include <stdlib.h>
int main() 
 { 
   char *string; 
   string = (char* ) malloc (10); 
   printf("Input a string:"); 
   gets(string); 
   printf("The string input was: %s\n",string); 
   return 0; 
 } 

Example : Using common file I/O operation /* Create backup text file */ 
#include <stdio.h>
int main()
{ 
  FILE *in, *out; 
  if ((in = fopen("\\AUTOEXEC.BAT", "rt"))== NULL) 
   { 
    fprintf(stderr, "Cannot open input file.\n");
    return 1; 
   } 
  if ((out = fopen("\\AUTOEXEC.BAK", "wt"))== NULL) 
   { fprintf(stderr, "Cannot open output file.\n"); 
     return 1; 

   } 
   while (!feof(in)) /* feof check for end of file */ 
    fputc(fgetc(in),out); /* fputc put char in the file */ 
   fclose(in); 
   fclose(out); 
   return 0; 
} 

Example: Reading from text file 
#include <stdio.h>
#include <stdlib.h>

int main () 
 { FILE *fp; 
   int i; 
   float x[10]; // array 0..9 of float
   if ( (fp=fopen("c:\\tc\\bin\\data.dat","r")) ==NULL)
    { 
      printf("Error in opening data file \n"); 
      exit (1);
    } 
   i=0; 
   while (!feof(fp)) 
    { 
     fscanf (fp,"%f",&x[i]); /* read from text file */ 
     printf ("%.2f\n",x[i]); /* print with 2 decimal places */ 
     i++; 
    } 
   return 0; 

} 

13.0 Common C/C++ programming pitfalls.

 
Belows are the most common C errors: 
1. Misplacing a semicolon. 
  Example: 
if (j==100); /* a null statement ? */ j=0; 
/* j will always sets to 0 due to misplace semicolon */ 

2.Confusing the operator = with == 
Example: 
if (a=2) /* this is an assignment statement !!!!*/ 
printf ("Your turn\n");

3.Confusing a character constant and a character string. 
Example: 
textchar='a';/* a single character , declared as char */ textstring="a" /*a single string, declared as pointer to char *char */ 
4.Using the wrong bounds for an array 
Example: 
  int a[100],i,sum=0; .... 
  for (i=1;i<=100;++i) /* wrong, C array starts from 0, not 1*/ 
  sum +=a[i]; /* in this case a goes from 0..99 */ 

5.Forgetting to reserve an extra location in an array for the terminating null character of a string. The character string "hello"
requires a declaration of 6 character long array of char because every
string must have a null character at the of the string. 

6.Confusing the operator -> with operator >, or >>, when refering structure members. Remember the operator . is used for structure variables, while -> is used for structure pointer variables. 
Example: 
struct students 
 { 
  char *name; int age; 
 } 
int shifting=1; 
struct students lists; /* in C++ the keyword struct can be omitted */ 
struct students *listpntr; 
..... 
listpntr=&lists;
strcpy(list.name,"ahmad"); strcpy(listpntr->.name,"ahmad");
shifting= shifting<<2 /* shift left ot shifting <<=2 *, shifting
= 4/ 

7.Omitting the ampersand (&) before non-pointer variables in a scanf call. 
Example: int number; ... scanf ("%d",number) 
/*error here number should be &number */ 
Remember that all arguments appearing after the format string in a scanf call must be pointers. 

8.Omitting the break statement at the end of a case in a switch statement.
Remember that if a break is not included at the end of a case, then execution
will continue into the next case. 

9.Inserting a semicolon at the end of preprocessor definition particularly define. 
Example: #define PI 3.14; /* error !!! no semicolon necessary */ 
Note another way of defining constant is as follows: 
         const Pi = 31.4; 

10.Using expression that has side effects in a macro call. 
Example: #define SQUARE (x) (x)*(x) ... W= SQUARE(++v);
The invocation of the SQUARE macro will cause v to be incremented twice,
since this statement will be expanded by the preprocessor to W=(++v)*(++v)

11.Not putting the braces where it is necessary. This error usually happens
when dealing with while,for, and do while statement. 
Example: Error using while 
n = 0; 
while (n<3) 
printf ("\n n is %d",n); /* infinite loop , should have braces*/ n++;

Reference:

The folowing books directly and indirectly have contributed to the development of this homepage and notes. As a disclaimer, I will not be responsible for any damages, lost of profit or any disasters as a result of using this notes.

1.Unix Primer Plus, Mitchell Waite,Martin and Stephen Prata,Howard W. Sams & Company
2.Turbo C++ User Manual, Borland International
3. Programming in C, Stephen G. Kochan, Hyden Books.
4. C Language Algorithms for Digital Signal Processing,Bruce Kimberly, Prentice Hall Inc.
5. Power C User Manual, Mix Software
6. Dos Programmers Reference, Que
7. C Step By Step, Michel Waite etc, Howard Sams & Company