Lecture 7: Structure and Class
 structure

solving quadric equations as an example
 class

air-plane and bullets.
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CS3369 Real Time Control
Software/Wang Lusheng
Computing the roots of a quadric equation
The roots of a quadric equation ax2+bx+c=0 are
x1= (-b+( b2-4ac))/2ac
x2=x1= (-b- ( b2-4ac))/2ac
void roots(float a, float b, float c)
{
if (b*b-4*a*c>=0)
{
x1=(-b+sqrt(b*b-4*a*c))/(2*a*c);
x2 =(-b-sqrt(b*b-4*a*c))/(2*a*c);
}
else
flag=1;
}
#include<iostream.h>
float x1, x2;
int flag=0;
void roots(float a, float b, float c)
void main(void)
{
x1, x2 and flag are used as global
roots(1.0,2.0, 1.0);
variables. Otherwise, function roots
if(flag == 0)
must return two values (we do not
cout<<“The roots are”<<x1<<x2;
know how to do it.)
else
cout<<“No real root”;
Page 2
5/29/2016 }
CS3369 Real Time Control
Software/Wang Lusheng
Define structures
• Structures are aggregate data types built using elements
of other types.
• We can use structure to group several variables together
struct two_roots {
float x1;
float x2;
} r;
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CS3369 Real Time Control
Software/Wang Lusheng
Define a function of two_roots type
• The function roots returns a value of type two_roots that
contains two values of type float.
struct two_roots roots (float a, float b, float c)
{ struct two_roots r;
if (b*b-4*a*c>=0)
{ r.x1=(sqrt (b*b-4*a*c)-b)/(2*a*c);
r.x2=(-sqrt(b*b-4*a*c)-b)/(2*a*c);}
else
x3=100;
return r;
}
5/29/2016
CS3369 Real Time Control
Software/Wang Lusheng
Page 4
Using structures in main()
• In main function, we can print the two roots as follows;
#include <iostream.h>
int x3;
struct two_roots {
float x1;
float x2;
};
struct two_roots roots (float a, float b, float c);
void main(void)
{ struct two_roots z;
z=roots(1.0, 2.0, 1.0);
if (x3==100)
cout<<“There is no real root”;
else
cout<<“The roots are”<< z.x1<<“ ”<<z. x2;
}
5/29/2016
struct two_roots roots (float a, float b, float c)
{ struct two_roots r;
if (b*b-4*a*c>=0)
{ r.x1=(sqrt (b*b-4*a*c)-b)/(2*a*c);
r.x2=(-sqrt(b*b-4*a*c)-b)/(2*a*c);
}
else
x3=100;
return r;
}
CS3369 Real Time Control
Software/Wang Lusheng
Page 5
Time Services (Clock)


struct the_time {int hrs, int mins, int secs, int hundth;};
struct the_time get_time() {

the_time tmp;

int i,j,k,l;

_AH=0x2C;
//service 0x2C for get time

interrupt(0x21);
//interrupt 0x21

i=_CH; j=_CL; k=_DH; l=_DL;

tmp.hrs=i;
tmp.mins=j;
tmp.secs=k;
tmp.hundth=l;

return tmp;

}

void main()

{ struct the_time x;

x=get_time();

cout<<“The hour is ”<<x.hrs<<“The minute is ”<<x.mins;

cout<<“The second is ”<<x.sees;
5/29/2016  }
CS3369 Real Time Control
Software/Wang Lusheng
Page 6
Problem Solving: Student Records
• We define a structure that can hold student records
structure student {
char name[20];
int student_id;
char grade;
};
struct student x;
void main()
{int j;
cout<<“Please enter your name with <=20 characters\n”;
for(j=0; j<=19; j++)
cin>>x.name[j];
cout<<“Please enter your student number\n”;
cin>>x.student_id;
cout<<“Please enter the grade (A, B, C, D, F) \n”;
cin>>x.grade;
} Question: How to print out those input records?
5/29/2016
CS3369 Real Time Control
Software/Wang Lusheng
The program asks
users to enter a
record of
students. Each
record contains
the name,
student_id and
grade.
Page 7
Problem Solving: Student Records
• We define a structure that can hold student records
structure student {
char name[20];
int student_id;
char grade;
};
struct student x[56];
void main()
{int i,j;
for(i=0; i<=55; i++)
{ cout<<“Please enter your name with <=20 characters\n”;
for(j=0; j<=19; j++)
cin>>x[i].name[j];
cout<<“Please enter your student number\n”;
cin>>x[i].student_id;
cout<<“Please enter the grade (A, B, C, D, F) \n”;
cin>>x[i].grade;
} Question: How to print out those input records?
The program asks
users to enter 104
records of
students. Each
record contains
the nemae,
student_id and
grade.
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CS3369 Real Time Control
Software/Wang Lusheng
Classes
• Classes enable the programmer to model objects that have
attributes (represented as data members) and behaviors or
operations (represented as member functions).
• Object-oriented programming models real-world objects
with software counterparts--classes
• Objects of the same class have the same characteristics
– e.g., cars, vehicles, air-planes, etc.
• OOP encapsulates data (attribute) and functions
(behavior) into packages called objects.
• Objects have the property of information hiding.
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CS3369 Real Time Control
Software/Wang Lusheng
Classes (continued)
• information hiding : objects may know how to
communicate with each other, but do not know how other
objects are implemented.
• We can build software by combining “standardized,
interchangeable parts” --classes.
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CS3369 Real Time Control
Software/Wang Lusheng
Define air-plane as a class
#include <graphics.h>
#include<dos.h>
#include<iostream.h>
#include<conio.h>
class Air{
public:
int size;
void planeshow(int i,int k);
void ereasep(int i, int k);
/*i decides the herizontal position */
/* k decides the vertical position */
};
void Air::planeshow(int i,int k)
{
int j;
circle(i+5, 200+size+k, size);
circle(i+3, 200+2*size+k, size);
for (j=0; j<=4+3*size; j=j+size)
circle(i+j, 200+k, size);
circle(i+5, 200-size+k, size);
circle(i+3, 200-2*size+k, size);
}
5/29/2016
void Air::ereasep(int i, int k)
{
int j;
setcolor(BLACK);
circle(i+5, 200+size+k, size);
circle(i+3, 200+2*size+k, size);
for (j=0; j<=4+3*size; j=j+1)
circle(i+j, 200+k, size);
circle(i+5, 200-size+k, size);
circle(i+3, 200-2*size+k, size);
}
char read_key()
{ int y=1;
char x;
_AH=0x01;
geninterrupt(0x16);
y=_FLAGS&0x40;
if(y == 0)
{
_AH=0x00;
geninterrupt(0x16);
x=_AL;
return x; }
return '?';
}
void main(void)
{
int driver = DETECT,mode;
int i,k,f=0,f3=0;
char x;
Air y1, y2, y3;
initgraph(&driver,&mode,"a:\\bgi");
setcolor(WHITE);
line(1,400,400,400);
for ( i = 0; i < 80; i++ )
{
setcolor(BLUE); y1.size=2; y1.planeshow(5*i, 5);
x=read_key();
if (x =='u') f=f-8;
if (x =='i') f=f+8;
if (x=='o') f3=f3-8;
if (x=='p') f3=f3+8;
setcolor(YELLOW); y2.size=4; y2.planeshow(5*(i-8), f);
setcolor(RED); y3.size=6;y3.planeshow(5*(i-16), f3);
delay (300);
y1.ereasep(5*i, 5); y2.ereasep(5*(i-8), f);
y3.ereasep(5*(i-16), f3);
}
closegraph();
}
CS3369 Real Time Control
Software/Wang Lusheng
Page 11
Define air-plane as a class
#include<dos.h>
#include <graphics.h>
#include<iostream.h>
#include<conio.h>
class Air{
public:
int size;
void planeshow(int i,int k);
void ereasep(int i, int k);
void shoot(int i, int k);
};
void Air::planeshow(int i,int k)
{
int j;
circle(i+5, 200+size+k, size);
circle(i+3, 200+2*size+k, size);
for (j=0; j<=4+3*size; j=j+size)
circle(i+j, 200+k, size);
circle(i+5, 200-size+k, size);
circle(i+3, 200-2*size+k, size);
}
void Air::ereasep(int i, int k)
{
int j;
setcolor(BLACK);
circle(i+5, 200+size+k, size);
circle(i+3, 200+2*size+k, size);
for (j=0; j<=4+3*size; j=j+1)
circle(i+j, 200+k, size);
circle(i+5, 200-size+k, size);
circle(i+3, 200-2*size+k, size);
}
5/29/2016
void main(void)
{
int driver = DETECT,mode;
int sf=0, i,k,f=0,f3=0;
char x;
Air y1, y2, y3;
void Air::shoot(int i, int k)
{int j; sound(700);
for(j=0; j<=10; j++)
{
setcolor(RED); line(i+j*30, 200+k,i+j*30+18, 200+k ); initgraph(&driver,&mode,"a:\\bgi");
delay (30);
setcolor(WHITE);
setcolor(BLACK); line(i+j*30, 200+k,i+j*30+18,
line(1,400,400,400);
200+k);
for ( i = 0; i < 120; i++ )
}
{
nosound();
setcolor(BLUE); y1.size=2; y1.planeshow(5*i, 5);
}
x=read_key();
if (x =='u') f=f-8;
if (x =='i') f=f+8;
char read_key()
if (x=='o') f3=f3-8;
{ int y=1;
if (x=='p') f3=f3+8;
char x;
setcolor(YELLOW); y2.size=3;
_AH=0x01;
y2.planeshow(5*(i-8), f);
geninterrupt(0x16);
setcolor(RED); y3.size=3;
y=_FLAGS&0x40;
y3.planeshow(5*(i-16), f3);
if(y == 0)
if(x=='k'){sf=1; y2.shoot(5*(i-8), f);}
{
if (sf==0) delay (300);
_AH=0x00;
else sf=0;
geninterrupt(0x16);
y1.ereasep(5*i, 5); y2.ereasep(5*(i-8), f);
x=_AL;
y3.ereasep(5*(i-16), f3);
return x; }
}
return '?';
closegraph();
Page 12
}
}
CS3369 Real Time Control
Software/Wang Lusheng
Define air-plane and Shoot classes
#include<dos.h>
#include <graphics.h>
#include<iostream.h>
#include<conio.h>
class Air{
public:
int size;
void planeshow(int i,int k);
void ereasep(int i, int k);
void shoot(int i, int k);
/*i decides the herizontal position */
/* k decides the vertical position */
};
void Air::planeshow(int i,int k)
{
int j;
circle(i+5, 200+size+k, size);
circle(i+3, 200+2*size+k, size);
for (j=0; j<=4+3*size; j=j+size)
circle(i+j, 200+k, size);
circle(i+5, 200-size+k, size);
circle(i+3, 200-2*size+k, size);
}
void Air::ereasep(int i, int k)
{
int j;
setcolor(BLACK);
circle(i+5, 200+size+k, size);
circle(i+3, 200+2*size+k, size);
for (j=0; j<=4+3*size; j=j+1)
circle(i+j, 200+k, size);
circle(i+5, 200-size+k, size);
circle(i+3, 200-2*size+k, size);
}
void Air::shoot(int i, int k)
{int j; sound(700);
for(j=0; j<=10; j++)
{
setcolor(RED); line(i+j*30, 200+k,i+j*30+18, 200+k ); delay
(30);
setcolor(BLACK); line(i+j*30, 200+k,i+j*30+18, 200+k);
}
nosound();
}
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CS3369 Real Time Control
Software/Wang Lusheng
Define air-plane and Shoot classes
class Shoot {
public:
void point(int i, int k);
void sh(int i, int k);
};
void Shoot::point(int i, int k)
{
setcolor(YELLOW); circle(400+i, 400+k, 1);
}
void Shoot::sh(int i, int k)
{int j; sound(900);
for(j=0; j<=10; j++)
{
setcolor(RED);
line(400-j*30+i, 400+k-30*j,400-j*30+i-10,
400+k-30*j-10); delay (30);
setcolor(BLACK);
line(400-j*30+i, 400+k-30*j,400-j*30+i-10,
400+k-30*j-10);
}
nosound();
}
char read_key();
void main(void)
{
int driver = DETECT,mode;
int sf=0, i,k,f=0,f3=0, xi=0, yi=0;
char x;
Air y1, y2, y3;
Shoot bullet;
initgraph(&driver,&mode,"a:\\bgi");
setcolor(WHITE);
line(1,400,400,400);
for ( i = 0; i < 80; i++ )
{
setcolor(BLUE); y1.size=2; y1.planeshow(5*i, 5);
x=read_key();
if (x =='u') f=f-8;
if (x =='i') f=f+8;
if (x=='o') f3=f3-8;
if (x=='p') f3=f3+8;
setcolor(YELLOW); y2.size=3; y2.planeshow(5*(i-8), f);
if(x=='k'){sf=1; y2.shoot(5*(i-8), f);}
setcolor(RED); y3.size=3;y3.planeshow(5*(i-16), f3);
bullet.point(xi,yi);
if(x=='l') bullet.sh(xi,yi);
if (sf==0) delay (300);
else sf=0;
y1.ereasep(5*i, 5); y2.ereasep(5*(i-8), f);
y3.ereasep(5*(i-16), f3);
}
closegraph();
}
char read_key()
{ int y=1;
char x;
_AH=0x01;
geninterrupt(0x16);
y=_FLAGS&0x40;
if(y == 0)
{
_AH=0x00;
geninterrupt(0x16);
x=_AL;
return x; }
return '?';
}
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CS3369 Real Time Control
Software/Wang Lusheng
Attributes of air-plane:
Another definition of class Air
void Air::ereasep(int i, int k)
#include <graphics.h>
{
#include<iostream.h>
int j;
#include<conio.h>
setcolor(BLACK);
class Air{
circle(i+5, 200+size+k, size);
public:
circle(i+3, 200+2*size+k, size);
int size; /** the size of the air-plane **/
for
(j=0; j<=4+3*size; j=j+1)
int i; /** the horizontal position **/
circle(i+j, 200+k, size);
int k /** the vertical position **//
circle(i+5, 200-size+k, size);
void planeshow();
circle(i+3, 200-2*size+k, size);
void ereasep();
}
};
void Air::planeshow()
{
int j;
circle(i+5, 200+size+k, size);
circle(i+3, 200+2*size+k, size);
for (j=0; j<=4+3*size; j=j+size)
circle(i+j, 200+k, size);
circle(i+5, 200-size+k, size);
#include<dos.h>
circle(i+3, 200-2*size+k, size);
}
5/29/2016
char read_key()
{ int y=1;
char x;
_AH=0x01;
geninterrupt(0x16);
y=_FLAGS&0x40;
if(y == 0)
{
_AH=0x00;
geninterrupt(0x16);
x=_AL;
return x; }
return '?';
}
CS3369 Real Time Control
Software/Wang Lusheng
size, and position.
void main(void)
{
int driver = DETECT,mode;
int i,k,f=0,f3=0;
char x;
Air y1, y2, y3;
initgraph(&driver,&mode,"a:\\bgi");
setcolor(WHITE);
line(1,400,400,400);
for ( i = 0; i < 80; i++ )
{
x=read_key();
if (x =='u') f=f-8;
if (x =='i') f=f+8;
setcolor(BLUE); y1.size=2;
y1.i=5*i; y1.k=f;
y1.planeshow(); /*y1.planeshow(5*i, f); */
delay (300);
y1.ereasep();
}
closegraph();
}
Page 15
Use of return statement
If the type of the function is not void, at least one return
statement must be used. The syntax of a return statement is:
return value;
Here value can be a number, variable or math expression.
Examples: return 0; return x; return (x+1-2*y);
Purposes:
1. Terminates the function.
2. Return a value to the parent function.
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CS3369 Real Time Control
Software/Wang Lusheng
A tricky example of return statement
#include<iostream.h>
int f(int i);
int f(int i)
{
if (i>3)
void main()
{
{ cout<<“good”
int x;
return i; }
else
x=f(5);
{cout<<“bad”;
}
return -999; }
}
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CS3369 Real Time Control
Software/Wang Lusheng
Local Variables
 Variables declared within the body of a
function are its local variables (we also say
the scope of these variables is the body of
this function.) (Look at an example)
 Variables declared within the body of the
main() function of a program is local to the
main() function.
 A local variable is completely unknown
outside its scope. Two local variables of
different scopes may have the same name.
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CS3369 Real Time Control
Software/Wang Lusheng
An Example for Local Variables
#include<iostream.h>
int speed(int i)
int speed(int i)
{
int main()
int y;
{ int x, y=100;
y=2.1*i-0.15*i*i;
x=speed(10);
cout<< “The value of y inside speed()”<<y;
cout<< “The value of y inside main”<<y;
cout<<“\n”;
return 0;
}
return y;
}
Output:
The value of y inside speed() 6
The value of y inside main 100
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CS3369 Real Time Control
Software/Wang Lusheng
Variables in parameter list
 Variables declared in the parameter list of a function
are called formal variables. Their scope is the body of
this function.
 call-by-value mechanism: by default, when a
function is called, the value of the arguments are
plugged in the formal parameters. More specifically, if
the arguments are variables, their values not the
variables themselves are plugged in.
 call-by-reference mechanism (will not covered in this course)
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CS3369 Real Time Control
Software/Wang Lusheng
An Example for Local Variables
#include<iostream.h>
int speed(int i)
int speed(int i)
{
int main()
int y;
{ int x, y=100, j=10;
y=2.1*i-0.15*i*i;
x=speed(j);
cout<< “The value of y inside speed()”<<y;
cout<< “The value of y inside main”<<y;
cout<<“\n”;
return 0;
return y;
}
}
Output:
The value of y inside speed() 6
The value of j is passed
to speed(), not the
variable j.
The value of y inside main 100
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CS3369 Real Time Control
Software/Wang Lusheng
Global Variables
 Global variable: universal for the program, declared in
the program outside all functions. It can be used and
changed everywhere (by any function).
 Try to avoid using global variables.
#include<iostream.h>
int g;
void main()
{
int x,y;
x=11;
g=80;
y= f(5);
cout<<“The values of g , x and y in main()”
cout<<g<<“ ”<< x<<“ ”<<y;
}
int f(int i)
{int x=10;
cout<<“The values of g and x in side f()”;
cout<<g<<“ ” <<x<<“\n”;
g=g+i;
return g;
}
OUTPUT:
The values of g and x in side f() 80 10
The values of g , x and y in main() 85 11 85
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CS3369 Real Time Control
Software/Wang Lusheng
Another Example for Global Variables
The roots of a quadric equation ax2+bx+c=0 are
x1= (-b+( b2-4ac))/2ac
x2=x1= (-b- ( b2-4ac))/2ac
void roots(float a, float b, float c)
{
if (b*b-4*a*c>=0)
{
x1=(-b+sqrt(b*b-4*a*c))/(2*a*c);
x2 =(-b-sqrt(b*b-4*a*c))/(2*a*c);
}
else
flag=1;
}
include<iostream.h>
float x1, x2;
int flag=0;
void roots(float a, float b, float c)
void main(void)
{
x1, x2 and flag are used as global
roots(1.0,2.0, 1.0);
variables. Otherwise, roots must
if(flag == 0)
return two values that we do not
cout<<“The roots are”<<x1<<x2;
know how to do it.
else
cout<<“No real root”;
Page 23
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CS3369 Real Time Control
Software/Wang Lusheng
Global Variables vs Local Variables
 If global variables and local variables have the same
name, the local variables are valid within their scopes.
#include<iostream.h>
int g=30;
void main()
{
int x,y, g; /*g is a local variable */
x=11;
g=80;
y= f(5);
cout<<“The values of g , x and y in main()”
cout<<g<<“ ”<< x<<“ ”<<y;
}
int f(int i)
{int x=10;
cout<<“The values of g and x in side f()”;
cout<<g<<“ ” <<x<<“\n”;
/*g is a global variable */
g=g+i;
return g;
}
OUTPUT:
The values of g and x in side f() 30 10
The values of g , x and y in main() 80 11 35
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CS3369 Real Time Control
Software/Wang Lusheng
while statement
#include<iostream.h>
void main()
Syntax of while statement:
{
int a;
cout<<“please enter an integer in [1,9]\n”;
cin>>a;
while (logic_expression)
while (a<1 ||a>9)
{
{
cout<<“please enter an integer in [1,9]\n”;
statement1;
cin>>a;
}
statement 2;
}
….
}
(Demo the program in the lecture.The question
was given in Lab2 as extra exercise since you
have not learned while. It can be done using for
in a dirty way)
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Software/Wang Lusheng
Review and Exercises







variables
for statement
while statement
if statement
switch statement (optional)
while statement
functions
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CS3369 Real Time Control
Software/Wang Lusheng
Exercises
Question 1: Which of the following words can be
used as variable names?
1x11, x11, xx12, _abc, name_variable, for, if, for1,
1while.
Question 2. What are the outputs of the following
program?
for (i=1; i<5; i++)
#include<iostream.h>
{
void main()
for(j=1; j<=3; j++)
{
cout<<i<<j;
int i, j;
cout<“\n”;
}
}
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CS3369 Real Time Control
Software/Wang Lusheng
Page 27
Question 3. What are the outputs of the
following program?
Question 4. What are the outputs of the
following program?
#include<iostream.h>
#include<iostream.h>
void main()
void main()
{
{
int i = 10;
int i, j;
for (i=1; i<=5; i++)
if(i<0) cout <<“negative”;
{
if (i>100) cout<<“too large”;
for (j=1; j<=i; j++)
if (i>=75 && i<=100)
cout<<“ ”; /* There is one space*/
cout<<“excellent”;
cout <<“**** \n”;
}
}
}
What if the initial value is 88?
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CS3369 Real Time Control
Software/Wang Lusheng
Question 5. What are the outputs of the
following program?
Question 6. What are the outputs of the
following program?
#include<iostream.h>
#include<iostream.h>
void main()
int max (int x, int y);
{
void main()
int i;
{
i=1;
int temp_max, temp_max1;
while(i<=5)
temp_max=max(x1,x2);
{
temp_max1=max(temp_max, x3);
}
}
int x1=100, x2=102, x3=99;
cout<<i;
cout<<“The maximum is”;
i=i+1;
cout << temp_max1;
}
int max (int x, int y)
{ int temp=x;
if (y>temp) temp=y;
return temp;
}
5/29/2016
CS3369 Real Time Control
Software/Wang Lusheng
Page 29
Question 7. What are the outputs of the
following program?
#include<iostream.h>
int max (int x, int y, int z);
void main()
{
Question 8. What are the outputs of the following program?
#include<iostream.h>
int max (int x, int y, int z);
void main()
{
int x1=100, x2=102, x3=99;
temp_max=max(99, 102, 166);
int temp_max;
cout<<“The maximum is”;
temp_max=max(x1,x2,x3);
cout<<“The maximum is”;
cout << temp_max;
}
cout << temp_max;
}
int max (int x, int y, int z)
{
int max (int x, int y, int z)
{
int temp=x;
cout<<“The input numbers are”<<x<<y<<z<<“\n”;
int temp=x;
if (y>temp) temp=y;
if (y>temp) temp=y;
if(z>temp) temp=z;
if(z>temp) temp=z;
return temp;
int temp_max;
return temp;
}
}
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CS3369 Real Time Control
Software/Wang Lusheng
Question 9. What are the
outputs of the following
program?
#include<iostream.h>
int computation(int x);
void main()
{ int z, w, w1,x=10;
/* x he is a variable that can
be used in main() */
z=computation(5);
w=computation(z);
w1=computation(x);
cout<<z<<w<<w1
}
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int computation(int x)
/*x here is a formal
parameter */
{ int y;
y=x*x+25;
cout<<“input
is”<<x<<“\n”;
return y;
}
CS3369 Real Time Control
Software/Wang Lusheng
Page 31
Question 10. What are the outputs
of the following program?
int max ()
{ int temp=x;
#include<iostream.h>
cout<<“The input numbers are”;
int x, int y, int z;
cout <<x<<y<<z<<“\n”;
int max ();
if (y>temp) temp=y;
void main()
{
if(z>temp) temp=z;
int temp_max;
x=90;
y=91;
z=z+1;
z=92;
return temp;
cout<<z<<“\n”;
temp_max=max();
}
cout<<“The maximum is”;
cout << temp_max;
cout<<z;
}
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CS3369 Real Time Control
Software/Wang Lusheng
Question 11. (Moderate) Write a function that takes three integers as its input
parameters and outputs the smallest number among the three integers. The
prototype of the function is as follows:
int minmum(int x, int y, int z);
Question 12. (Hard) Write a program that (1) asks the user to input an integer from
the screen, (2) the input integer should be in the range [0, 100] or [200, 300],
and (3) if the input integer is not in the required ranges, ask the user to re-enter the
integer until the integer is in the required ranges.
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CS3369 Real Time Control
Software/Wang Lusheng