Evaluation of the Course (Modified)
 Assignments: 40%

Assignment: My part 20% and Dr. Lam’s part 20%

MY PART: (2 assignments done in lab, 10% each)

 A final exam:
60%;
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CS3369 Real Time Control
Software/DENG Xiaotie
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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Software/DENG Xiaotie
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/DENG Xiaotie
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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Software/DENG Xiaotie
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/DENG Xiaotie
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/DENG Xiaotie
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/DENG Xiaotie
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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Software/DENG Xiaotie
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”;
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CS3369 Real Time Control
Software/DENG Xiaotie
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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Software/DENG Xiaotie
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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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/DENG Xiaotie
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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Page 13
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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Software/DENG Xiaotie
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;
}
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Software/DENG Xiaotie
Page 15
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/DENG Xiaotie
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/DENG Xiaotie
Page 17
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/DENG Xiaotie
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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Software/DENG Xiaotie