Lecture 5: Interrupts in Turbo C++
 Concepts of Interrupts
 Programs for interrupts:



Keyboard
Video
Time
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Execution of an Instruction (review)
Execution of
an instruction
is achieved by
a sequence of
commands
issues by the
control unit.
Fetch the instruction from the memory
Fetch the operands from the memory
Perform the operation
Update the program counter
no
Check interrupt
yes
Interrupt processing
Next Instruction
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Execution of a Program (review)
Fetch the instruction from the memory
Fetch the operands from the memory
Perform the operation
Update the program counter
A program is
a sequence of
instructions.
no
LOAD b, R1
Check interrupt
yes
Fetch the instruction from the memory
Fetch the operands from the memory
Perform the operation
Update the program counter
no
Check interrupt
yes
ADD R1, 1
a = b + 1;
Fetch the instruction from the memory
Fetch the operands from the memory
Perform the operation
Update the program counter
no
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STORE R1, a
Check interrupt
yes
…...
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Page 3
Interrupt
• Interrupt is a mechanism for diverting
the attention of a processor when a
particular event occurs, such as I/O device
requests.
• Interrupts cause a break in the normal
execution of a program.
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A Break in the Normal Execution of a Program
Fetch the instruction from the memory
Interrupt
Fetch the operands from the memory
Perform the operation
Update the program counter
no
The execution of the
program can be temporarily
stopped to allow a special
piece of software -- an
interrupt service routine -to run. When the routine
has finished, the program
resumes.
Check interrupt
yes
Fetch the instruction from the memory
Fetch the operands from the memory
Perform the operation
Update the program counter
Check interrupt
yes
Fetch the instruction from the memory
Interrupt
Processing and
Service
Fetch the operands from the memory
Perform the operation
Update the program counter
no
Check interrupt
yes
Interrupt processing
+ efficient and responsive
- difficult to program
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Steps taken to process Interrupt
1.
On receipt of the interrupt, the processor after executing
the current instruction, branches to an interrupt processing
routine. The routine is commonly known as Interrupt Handler.
2.
The Interrupt Handler will save the current processor
data (registers, status register, PC) and determine which device
has interrupt the processor (polling).
3.
Execution then branches to the so called Interrupt
Service Routine associated with the device (causing the
interrupt) and the processor executes data transfer.
4.
The interrupt system is enable so that further interrupts
may be recognized.
5.
Return to that program the execution of which was
suspended after recognizing the interrupt.
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Interrupt
Processing
and Service
Disable interrupts
Save environment
Find out which device causes interrupt
Branch to specific interrupt service routine
ISR 1
ISR i
ISR n
Restore environment
Enable interrupts
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Interrupt Vectors
the segmented addresses that specify the locations of
interrupt handlers are called interrupt “vectors”
•
•an interrupt handler is a function/subroutine that takes
care of the interrupt.
• There are 256 interrupt vectors stored in interrupt vector
table located at the beginning of the memory
•some are reserved and some can be used by users
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Types of Interrupt
• Hardware Interrupts
• CPU Interrupts
• Software Interrupts
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Hardware Interrupts
Hardware interrupts are generated by device control and
supervised by PIC (programmable interrupt control) chip.
Interrupt No. Functions








0x02
0x08
0x09
0x0A
0x0B, 0x0C
0x0D
0x0E
0x0F
NMI: non-maskable interrupt, memory parity
timer (18 per second)
keyboard
interrupt from controller 2
serial port2,1
parallel port 2
diskette
parallel port 1 (for printer)
Here, NMI has top priority and is serviced immediately, and it cannot be turned off. It
occurs due to some significant error, such as power failure.
HERE: 0x stands for hexadecimal notations: 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F, where A
stands for ten, B eleven, C, twelve, D thirteen, E fourteen, F fifteen. Therefore, 0x200 is
2x16x16 plus 0 which is 512 in decimal. For decimal notations: 200=2x10x10.
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CPU Interrupts
CPU interrupts are generated in response to a fatal
program error, or for program flow control
 0x00
 0x01
instruction
 0x02
by user
 0x04
division by zero
generated after every
when in single-step mode
generated when a program
reaches a breakpoint set
arithmetic overflow
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Software Interrupts
Software interrupts are generated by using the software interrupt
instruction. In turbo C:
#include <dos.h>
geninterrupt(n);
 BIOS interrupts: provides the most direct, low level
interaction with the I/O devices and give a deviceindependent interface which hides all the details of the
hardware architecture from programmers and includes
interrupt numbers: 0x05, 0x10-0x1C, 0x48.
 DOS interrupts: are parts and the DOS operating system,
handle file and memory management and executive
services: 0x20-0x60
 General use interrupts: can be written by users for their
own service routines: 0x61-0x67
Notice: no need to remember all the interrupt vectors.
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Focus on
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A Register
INPUT
OUTPUT
Q
D
CLOCK
D: data input
Q: output of data
in the register
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Architecture of PC Registers
Scratch-pad Registers














AX (accumulator)
BX (base)
CX (count)
DX (data)
CS (code segment)
DS (data segment)
SS (stack segment)
ES (extra segment)
IP (instruction pointer)
SP (stack pointer)
BP (base pointer)
SI (source index)
DI (destination index)
Flags
AH
BH
CH
DH
7
OF DF
0
7
AL
BL
CL
DL
0
15
Segment Registers
0
15
Offset Registers
0
IF TF
SF
ZF
AF
PF
CF
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Access Registers in Turbo C
REGISTERS
•
•
•
•
•
•
•
•
•
•
•
•
•
AX
BX
CX
DX
CS
DS
SS
ES
SP
BP
SI
DI
Flags
PSUDO-VARIABLES in C
_AX (_AH _AL)
_BX (_BH, _BL)
_CX (_CH, _CL)
_DX (_DH, _DL)
_CS
_DS
_SS
_ES
_SP
_BP
_SI
_DI
_FLAGS
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The Flag Register in IBM PC
15
0
OF DF
IF TF
SF
ZF
AF
PF
CF
IF is the interrupt flag which controls whether interrupts are
enabled.
IF=1:
The CPU will deal with interrupt requests.
IF=0:
The CPU will ignore interrupt requests.
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CF Carry flag
Indicates an arithmetic carry
OF Overflow flag Indicates a signed arithmetic overflow
ZF Zero flag
Indicates a zero result or an equal comparison
SF Sign flag
Indicates a negative result or comparison
PF Parity flag
Indicates an even number of 1 bits
AF Auxiliary carry flag ….
DF Direction flag Controls increment direction in string
operastions
TF Trap flag
Controls single-step operation (used by
DEBUG).
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Page 16
BIOS Keyboard Services
They are invoked with interrupt 0x16 with the following
Service numbers in the register AH (_AH in Turbo C).
service#
functionality








0x00
0x01
0x02
0x03
0x05
0x10
0x11
0x12
Read Next Keyboard Character
Report Whether Character Ready
Get Shift Status
Set Typematic Rate and Delay
Keyboard Write
Extended Keyboard Read
Get Extended Keystroke Status
Get Extended Shift Status
Notice:
1. Service numbers are parameters pass to the subroutines/interrupt handlers
2. Try to remember the meaning of service 0x00 and 0x01 for interrupt 0x16.Page 17
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Interrupt 0x16 Service 0x00
Service 0x00 reports the next keyboard input character.
If there is no character in the BIOS keyboard buffer, it
waits until one is ready. The character is removed from
the BIOS keyboard buffer after it is read.
 Each character is reported as
a pair of bytes. The main
byte returned in AL is either
0 for special characters, or an
ASCII code for ASCII
characters.
 The auxiliary byte returned
in AH is either the character
ID for special characters or
the standard PC-keyboard
scan code identifying the
pressed key.
To invoke this service to read a character
into a variable x in Turbo C, we do:
char x; _AH=0x0; geninterrupt(0x16); x=_AL;
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Page 18
An Example of Getting a Key from Keyboard





char x; int y;
_AH=0x0;
geninterrupt(0x16);
x=_AL;
cout <<“The key is: ”<< x <<endl;





declare x to be “char” type
choose service 0x0 with _AH
invoke interrupt 0x16
get ASCII code of key from _AL
print the key out
Remember to include dos.h in your file.
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A Function to get a key
 char get_key_number () {

char a;

_AH=0x00;

geninterrupt(0x16);

a=_AL;

return tmp;

}
//return type of the function is char
//service number 0x00
//interrupt 0x16
//_AL is the key
//return the value
Demo the program A:key.cpp in the lecture.
1. Show the program
2. Run the program
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Interrupt 0x16 Service 0x01
Service 0x01 tests whether a keyboard input character is
ready. The zero flag (ZF) is used as the signal: 1 indicates
no input is ready, 0 indicates a character is ready.
In the latter case, the character is not removed from
the BIOS keyboard buffer until it is read by service 0x00.
To invoke this service in Turbo C, we do:
char x; _AH=0x01; geninterrupt(0x16);
To test whether a character is ready after the above
steps in Turbo C, we do:
if (_FLAGS&0x40==64);
to check whether ZF is 1.
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Use Keyboard BIOS to Read
 To write a program to read a char from BIOS keyboard
buffer, one may first use service 0x01 interrupt 0x16 to
test whether there is a key stored in the BIOS buffer,
then use service 0x00 interrupt 0x16 to read it.

int ch;
_AH=0x01;
geninterrupt(0x16);
temp=_FLAGS&0x40;

/*must put the data to temp, see slide 32 */




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The difference is that the
computer does not have to
wait for users to type it.
if (temp==0) {
– _AH=0;
– geninterrupt(0x16);
– ch=_AL;
}
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Page 22
Caution when using Pseudo-Variables
Pseudo-variables refer to CPU registers which are used by
other programs which may run at the same time. One must
assign values right before using them and read values right
after obtaining them, especially when we program in C. Be
careful about the following:
 A pseudo-variable has no address
 The values one place in pseudo-variables may NOT be
preserved for any length of time.
 Values of pseudo-variables may not remain the same across
a function call.
 Do not change values of _CS, _SS, _SP, nor _BP since they
are used by machine code produced by Turbo C compiler.
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Write a function to get a character

int key_ready() {//return 1 if a key is ready, 0 otherwise
•
•
•
•
•
•


long int x;
_AH=1;
geninterrupt(0x16);
x=_FLAGS;
if (x&0x40==0) {return 1;}
else return 0;
}
char read_a_key() {
//service number 0x01
//interrupt 0x16
//get flag register
//if ZF==0 a key is ready
//else no key
//return char if a key is ready
• if (key_ready())
• {return get_key_number().x;}
• else return 0;

}
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Shoot a bullet when press a key
#include<dos.h>
#include <graphics.h>
#include<iostream.h>
#include<conio.h>
void show(int i,float h, float v);
void erease(int i, float h, float v);
void main(void)
{
int driver = DETECT,mode;
int i,j,i1,s1;
int y=1;
initgraph(&driver,&mode,"D:\\bc31\\bgi");
setcolor(WHITE);
line(1,400,400,400);
for ( i = 0; i < 80; i++ )
{
show(i, 5.0, 9.0);
y=1;
_AH=0x01;
geninterrupt(0x16);//
y=_FLAGS&0x40;
if(y == 0)
{s1=1;i1=i;
_AH=0x00;
geninterrupt(0x16);}
if (s1==1) {show(i-i1, 10.0, 8.0); }
delay (300);
erease(i, 5.0, 9.0);
if (s1==1) erease(i-i1, 10.0, 8.0);
}
closegraph();
}
void show(int i, float h, float v)
{ int x, y;
x=h*i;
y=v*i-0.15*i*i;
setcolor(RED);
circle(400-x,400-y,2);
}
void erease(int i, float h, float v)
{
int x, y;
x=h*i;
y=v*i-0.15*i*i;
setcolor(BLACK);
circle(400-x,400-y,2);
}
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Video Interrupt Services(for general knowledge, will not be tested)
Most of the useful video services are found in the BIOS
through interrupt 0x10. Some MS-DOS video services
are provided through interrupt 0x21. They are user
programmed interrupts to produce output to the video
screen. Usually, one puts the function/service number in
the register AH and then invokes the corresponding
interrupt. Very often there are some parameters for these
functions/services which are put in register AL, BX, CX,
or DX.
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BIOS Video Service Interrupt 0x10
service# functionality












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0x00
0x01
0x02
0x03
0x04
0x05
0x06
0x07
0x08
0x09
0x0A
0x0B
service# functionality
set video mode
set cursor size
set cursor position
read cursor position
read light-pen position
set active display page
scroll window up
scroll window down
read character/attribute
write character/attribute
write character
set 4-color palette
•
•
•
•
•
•
•
•
•
•
•
•
0x0C write pixel
0x0D read pixel
0x0E write char in tty mode
0x0F get current video mode
0x10 color palette interface
0x11 char generator interface
0x12 alternate select
0x13 write character string
0x14/15 (PC convertible only)
0x1A read/wri. dsp. cmb. code
0x1B return functionality
0x1C save/restore video statePage 27
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Interrupt 0x10 Service 0x0E: Write char in TTY mode
.
 The service number 0x0E is put in register AH.
 The char to be written is put in AL. The display page
number is put in BH and the foreground color is in BL.
 The character is written at the cursor location, and the
cursor is advanced one position, wrapping over to new
line or scrolling the screen as needed.
 There are four characters that service 0x0E reacts to
according to their ASCII meaning: 0x07 beep, 0x08
backspace, 0x0A linefeed, 0x0D carriage return. All
other characters are displayed normally.
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Output Characters
Display character “a”




_AH=0x0E;
_AL=97;
_BH=1;
geninterrupt(0x10);
Feed a new line
•
•
•
•
Back one space
•
•
•
•
_AH=0x0E;
_AL=0x08;
_BH=1;
geninterrupt(0x10);
_AH=0x0E;
_AL=0x0A;
_BH=1;
geninterrupt(0x10);
Beep
•
•
•
•
_AH=0x0E;
_AL=0x07;
_BH=1;
geninterrupt(0x10);
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A Function for Output a Char
 void output_a_char(int x) {




 }
//x is the ASCII code of char
_AH=0x0E;
_AL=x;
_BH=1;
geninterrupt(0x10);
Call the function to output characters
•
•
•
•
output_a_char(97);
output_a_char(8);
output_a_char(7);
output_a_char(0x0A);
//output ‘A’
//backspace
//output a ring
//a new line
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Another Function for Output a Char
 void output2_a_char(char x) {






int tmp;
tmp=x;
_AH=0x0E;
_AL=tmp;
_BH=1;
geninterrupt(0x10);
//x is a char type
//convert to ASCII code
//service number 0x0E
//output tmp
//interrupt 0x10
 }
Call the function to output characters
• output2_a_char(‘A’);
• output2_a_char(‘B’);
//output “A”
//output “B”
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Time Services (Clock)
 Interrupt 0x21 Service 0x2C:
 CH contains the hours (0-23)
 CL contains the minutes (0-59)
 DH contains the seconds (0-59)
 DL contains hundredths of a second (0-99).
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Time Services (Clock)





int i,j,k,l;
_AH=0x2C;
//service 0x2C for get time
interrupt(0x21);
//interrupt 0x21
i=_CH; j=_CL; k=_DH; l=_DL;
cout<<i<<“ Hours”<<j<<“ Minutes ”<<k<<“ Seconds ”<<l;
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Get the Time of Hitting a Key
Using the above functions written with interrupts, we
may obtain the approximate time of hitting a key as
follows:
int i,j,k,l;
read_a_key(); /*call function read_a_key(); */
_AH=0x2C;
//service 0x2C for get time
interrupt(0x21);
//interrupt 0x21
i=_CH; j=_CL; k=_DH; l=_DL;
cout<<i<<“ Hours”<<j<<“ Minutes ”<<k<<“ Seconds ”<<l;
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Arrays
 An array is a collection of two or more adjacent
memory cells, called array elements, that are
associated with a particular symbolic name.
To declare an array
int x[3];
x[0] x[1]
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(We declared an array with name x. It contains
3 elements. Each is of int type.The index starts with 0)
x[2]
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Use an array in the program

include <iostream.h>
The index of the
elements can change.
The index of the first
element of an array is
0.
void main(void)
{
int x[10],i;
for (i=0; i<=9; i++)
cin>>x[i];
x[0], x[1], x[2], x[3], x[4]
x[5], x[6], x[7], x[8], x[9]
for (i=0; i<=9; i++)
cout<< x[i];
}
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Initialize an array

include <iostream.h>
void main(void)
{
int x[10]={1,2,2,2,3,4,5,6,7,9} ,i;
for (i=0; i<=9; i++)
cout<< x[i]<<“ ”;
}
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An array of characters
include <iostream.h>
void main(void)
{
char x[3]={‘a’, ‘b’, ‘c’} ,i;
for (i=0; i<=9; i++)
cout<< x[i];
}
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Exercise
What does the following program output?
include <iostream.h>
void main(void)
{
int x[10]={8, 7, 9, 10, 1, 3, 3, 8, 2, 5} , i, j;
for (i=0; i<=9; i++)
{
for(j=9; j>i; j--)
if (x[i]>x[j])
{ y=x[i];
x[i]=x[j];
x[j]=y; }
for(j=0; j<=9; j++)
cout<< x[j];
cout<<“\n”;
}
}
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Shoot bullets whenever press key
#include<dos.h>
#include <graphics.h>
#include<conio.h>
void show(int i,float h, float v);
void erease(int i, float h, float v);
void planeshow(int i);
void ereasep(int i);
void main(void)
{
int driver = DETECT,mode;
int i,j,i1,s1,k;
int y=1;
int a[100];
for(i=0; i<=99; i++)
a[i]=0;
y=1;
_AH=0x01;
geninterrupt(0x16);//
y=_FLAGS&0x40;
if(y == 0)
{j=j+1;a[j]=i;
_AH=0x00;
geninterrupt(0x16);}
for (k=2; k<=j; k++)
if (a[k]!=0) {show(i-a[k], 10.0+0.5*k, 8.0+0.1*k); }
delay (300);
ereasep(5*i); ereasep(5*(i-8));
erease(i, 5.0, 9.0);
for (k=2; k<=j; k++)
if (a[k]!=0) {erease(i-a[k], 10.0+0.5*k, 8.0+0.1*k); }
}
initgraph(&driver,&mode,"D:\\bc31\\bgi")
closegraph();
;
}
setcolor(WHITE);
void show(int i, float h, float v)
line(1,400,400,400);
{ int x, y;
j=1;
x=h*i;
for ( i = 0; i < 80; i++ )
y=v*i-0.15*i*i;
{
setcolor(RED);
setcolor(BLUE); planeshow(5*i);
circle(400-x,400-y,2);
setcolor(YELLOW); planeshow(5*(i-8)); }
show(i, 5.0, 9.0);
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+plane
void erease(int i, float h, float v)
{
int x, y;
x=h*i;
y=v*i-0.15*i*i;
setcolor(BLACK);
circle(400-x,400-y,2);
}
void planeshow(int i)
{
int j;
circle(i+5, 202, 2);
circle(i+3, 204, 2);
for (j=0; j<=8; j++)
circle(i+j, 200, 2);
circle(i+5, 198, 2);
circle(i+3, 196, 2);
}
void ereasep(int i)
{
int j;
setcolor(BLACK);
circle(i+5, 202, 2);
circle(i+3, 204, 2);
for (j=0; j<=8; j++)
circle(i+j, 200, 2);
circle(i+5, 198, 2);
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circle(i+3, 196, 2);
}
a-shoot bullet
#include<dos.h>
#include <graphics.h>
#include<conio.h>
void show(int i,float h, float v);
void erease(int i, float h, float v);
void planeshow(int i,int k);
void ereasep(int i, int k);
void main(void)
{
int driver = DETECT,mode;
int i,j,i1,s1,k;
int y=1,xx=0;
char x;
int a[100];
for(i=0; i<=99; i++)
a[i]=0;
initgraph(&driver,&mode,"a:\\bgi");
setcolor(WHITE);
line(1,400,400,400);
j=1;
for ( i = 0; i < 80; i++ )
{
setcolor(BLUE); planeshow(5*i, 5);
show(i, 5.0, 9.0);
y=1;
_AH=0x01;
geninterrupt(0x16);
y=_FLAGS&0x40;
5/29/2016
u-plane up i-plane down
if(y == 0)
{
_AH=0x00;
geninterrupt(0x16);
x=_AL;
if (x == 'a') {j=j+1;a[j]=i;}
if (x =='u' ) {sound(700); xx=xx-5;}
if (x =='i' ) {sound(200); xx=xx+5;}
}
setcolor(YELLOW); planeshow(5*(i-8), xx);
for (k=2; k<=j; k++)
if (a[k]!=0) {show(i-a[k], 10.0+0.5*k, 8.0+0.1*k); }
delay (300);
nosound();
ereasep(5*i, 5); ereasep(5*(i-8), xx);
erease(i, 5.0, 9.0);
for (k=2; k<=j; k++)
if (a[k]!=0) {erease(i-a[k], 10.0+0.5*k, 8.0+0.1*k); }
}
closegraph();
}
void show(int i, float h, float v)
{ int x, y;
x=h*i;
y=v*i-0.15*i*i;
setcolor(RED);
circle(400-x,400-y,2);
}
CS3369 Real Time Control
Software/DENG Xiaotie
void erease(int i, float h, float v)
{
int x, y;
x=h*i;
y=v*i-0.15*i*i;
setcolor(BLACK);
circle(400-x,400-y,2);
}
void planeshow(int i,int k)
{
int j;
circle(i+5, 202+k, 2);
circle(i+3, 204+k, 2);
for (j=0; j<=8; j++)
circle(i+j, 200+k, 2);
circle(i+5, 198+k, 2);
circle(i+3, 196+k, 2);
}
void ereasep(int i, int k)
{
int j;
setcolor(BLACK);
circle(i+5, 202+k, 2);
circle(i+3, 204+k, 2);
for (j=0; j<=8; j++)
circle(i+j, 200+k, 2);
circle(i+5, 198+k, 2);
circle(i+3, 196+k, 2);
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}