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Object Manipulation

Module by: Dr. Duong Tuan Anh

1. OBJECTIVE

The objectives of Lab session 9 are (1) to learn to write parameterized constructor, constructor with default arguments and (2) to practice destructors.

2. EXPERIMENT

2.1 Run the following program in a C++ environment.
class Int{
private:
int idata;
public:
Int(){
idata=0;
cout<<"default constructor is called"<<endl;
}
Int(int d=9){
idata=d;
cout<<"constructor with argument is called"<<endl;
}
void showData(){
cout<<"value of idata: "<<idata<<endl;
}
};
void main()
{
Int i;
Int j(8);
Int k=10;
}
a. Explain why the program incurs a compile-time error.
b. Modify the program in order to remove the above error. Run the modified program.
  • Run the following program in a C++ environment.
class Vector{
private:
int *value;
int dimension;
public:
Vector(int d=0){
dimension=d;
if (dimension==0)
value=NULL;
else{
value=new int[dimension];
for (int i=0; i<dimension; i++)
value[i]=0;
}
}
void showdata(){
for (int i=0; i<dimension; i++)
cout<<value[i];
cout<<endl;
}
~Vector(){
if (value!=NULL)
delete value;
}
};
void main()
{
Vector v(5);
v.showdata();
Vector v2(v);
v2.showdata();
}
a. Explain why the program incurs one memory error at run-time.
b. Now add the following code segment in the Vector class definition.
Vector(const Vector& v){
dimension = v.dimension;
value=new int[dimension];
for (int i=0; i<dimension; i++)
value[i]=v.value[i];
}
Check if the program still incurs the memory error or not. Explain why.
2.3 a. Test the following program in a Visual C++ environment:
class some{ // code segment a
public:
~some() {
cout<<"some's destructor"<<endl;
}
};
void main() {
some s;
s.~some();
}
What is the output of the above program during execution? Explain the output.
b. Test the following program in Visual C++ environment:
class some{ // code segment b
int *ptr;
public:
some(){
ptr= new int;
}
~some(){
cout<<"some's destructor"<<endl;
if (ptr!=NULL){
cout<<"delete heap memory"<<endl;
delete ptr;
}
}
};
void main()
{
some s;
// s.~some();
}
What is the output of the above program during execution? Explain the output.
c. In the main() function of the program in b, if we remove the two slashes (//) before the statement s.~some(); then what the result is when the program is executed ? Explain why.
2.4 Given the class definition as follows:
class Auto {
public:
Auto(char*, double);
displayAuto(char*, double);
private:
char* szCarMake;
double dCarEngine;
};
Auto::Auto(char* szMake, double dEngine){
szCarMake = new char[25];
strcpy(szCarMake, szMake);
dCarEngineSize = dCarEngine;
}
Auto::displayAuto(){
cout<< “The car make: “<< szCarMake<< endl;
cout<< “The car engine size: “<< dCarEngine<< endl;
}
void main(){
Auto oldCar(“Chevy”, 351);
Auto newCar(oldCar);
oldCar.displayAuto();
newCar.displayAuto();
}
  1. Add an appropriate copy constructor to the Auto class .
  2. Add an appropriate destructor to the Auto class .
c. Run all the modifications in a C++ environment.

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