Chapter 10

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Chapter 10

Pointers and Dynamic Arrays

This activity contains 10 questions.

Which of the following is not a valid way to dereference pointer p to access the num field?


class MyInt {
  public: 
    int num;
};

MyInt *p;

*p.num;(*p).num;p->num;((*p).num);

Which line of the code below will cause a compiler error?


int* p1,p2;
int x = 3;
p1 = &x;
p2 = &x;

p2 = &x;int* p1, p2;int x = 3;p1 = &x;

What will the following program output?


class MyInt {
  public: 
    int num;
};

int main()
{
	MyInt *p1;
	MyInt *p2;

	p1->num = 10;
	p1 = p2;
	cout << p1->num << " " << p2->num << endl;
	return 0;
}

10 1010 0It will likely crash because it tries to store 10 into p1->num when no space has been allocated for p1's MyInt object. Memory should be allocated using new.10 (blank)

What will the following code output?


class MyInt {
  public: 
    int num;
	MyInt();
	MyInt(int n);
};

MyInt::MyInt() 
{
}

MyInt::MyInt(int n)
{
	num=n;
}

void DoSomething(MyInt *ptrA, MyInt *ptrB)
{
	int x = ptrA->num;
	ptrA->num = ptrB->num;
	ptrB->num = x;
}

int main()
{

	MyInt *p1;
	MyInt *p2;

	p1 = new MyInt(3);
	p2 = new MyInt(4);
	
	DoSomething(p1,p2);

	cout << p1->num << " " << p2->num << endl;

	return 0;
}

3 33 44 34 4

What will the following code output?


class MyInt {
  public: 
    int num;
	MyInt();
	MyInt(int n);
};

MyInt::MyInt() 
{
}

MyInt::MyInt(int n)
{
	num=n;
}

void DoSomething(MyInt *ptrA, MyInt *ptrB)
{
	ptrA = new MyInt(103);
	ptrB = new MyInt(104);
	cout << ptrA->num << " " << ptrB->num << endl;
}

int main()
{

	MyInt *p1;
	MyInt *p2;

	p1 = new MyInt(3);
	p2 = new MyInt(4);
	
	DoSomething(p1,p2);

	cout << p1->num << " " << p2->num << endl;

	return 0;
}

103 104
103 1043 4 3 43 4
103 104103 104
3 4

What will the following program output?


class MyInt {
  public: 
    int num;
	MyInt();
	MyInt(int n);
};

MyInt::MyInt() 
{
}

MyInt::MyInt(int n)
{
	num=n;
}

void DoSomething(MyInt **ptrA)
{
	cout << (*ptrA)->num << endl;
	delete (*ptrA);
	*ptrA = new MyInt(103);
	cout << (*ptrA)->num << endl;
}

int main()
{

	MyInt *p1;
	p1 = new MyInt(3);
	
	DoSomething(&p1);

	cout << p1->num << endl;

	return 0;
}

3
103
103

This code will cause an error because we are not allowed to use two **'s as an operator.

3
103
3

3
3
103

Give the output of the following code:


void DoSomething(char *s)
{
	char *p1,*p2,tmp;

	p1 = s;
	p2 = p1 + strlen(s)-1;
	while (p1<p2) {
		tmp = *p1;
		*p1 = *p2;
		*p2 = tmp;
		p1++;
		p2--;
	}
}

int main()
{
	char s[7] = "foobar";
	DoSomething(s);
	cout << s << endl;

	return 0;
}

rabrarThis will cause a compiler error because we are passing an array of char (char s[7]) as a pointer (char *s) in DoSomething.rabooffoobar

What is wrong with the following code fragment?


double *dArray = new double[100];
// Code here to use array
delete dArray;

The dynamic array should declared as: double[] dArray = new double[100];A pointer may not be declared to point to an array.To correctly delete memory allocated for an array, use delete[] dArray;To correctly delete memory allocated for an array, use delete *dArray;

Give the output of the following program:


class MyInt {
private:
    int *p_num;
public:
	MyInt();
	MyInt(int n);
	int GetNum();
	void SetNum(int n);
};

// Constructors
MyInt::MyInt() 
{
	p_num = new int;
	*p_num = -1;
}

MyInt::MyInt(int n)
{
	p_num = new int;
	*p_num = n;
}

int MyInt::GetNum()
{
	return *p_num;
}

void MyInt::SetNum(int n)
{
	*p_num = n;
}

int main()
{
	MyInt i1, i2(10);

	cout << i1.GetNum() << " " 
		<< i2.GetNum() << endl;

	i1 = i2;
	i2.SetNum(55);

	cout << i1.GetNum() << " " 
		<< i2.GetNum() << endl;
	
	return 0;
}

-1 10
55 55-1 10
-1 550 10
55 550 10
0 55

What is the output of the following code?


class MyInt {
private:
    int *p_num;
public:
	MyInt();
	MyInt(int n);
	int GetNum();
	void SetNum(int n);
	MyInt& operator=(const MyInt &rtSide);
};

// Constructors
MyInt::MyInt() 
{
	p_num = new int;
	*p_num = -1;
}

MyInt::MyInt(int n)
{
	p_num = new int;
	*p_num = n;
}

MyInt& MyInt::operator=(const MyInt &rtSide)
{
	*(this->p_num) = *(rtSide.p_num);
	return *this;
}

int MyInt::GetNum()
{
	return *p_num;
}

void MyInt::SetNum(int n)
{
	*p_num = n;
}

int main()
{
	MyInt i1, i2(10);

	cout << i1.GetNum() << " " 
		<< i2.GetNum() << endl;

	i1 = i2;
	i2.SetNum(55);

	cout << i1.GetNum() << " " 
		<< i2.GetNum() << endl;
	
	return 0;
}

-1 10
55 550 10
55 55-1 10
10 550 10
0 55

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Chapter 10

Which of the following is not a valid way to dereference pointer p to access the num field?
class MyInt { public: int num; }; MyInt *p;

Which line of the code below will cause a compiler error?
int* p1,p2; int x = 3; p1 = &x; p2 = &x;

What will the following program output?
class MyInt { public: int num; }; int main() { MyInt p1; MyInt p2; p1->num = 10; p1 = p2; cout << p1->num << " " << p2->num << endl; return 0; }

What is wrong with the following code fragment?
double *dArray = new double[100]; // Code here to use array delete dArray;

Chapter 10

Which of the following is not a valid way to dereference pointer p to access the num field? class MyInt { public: int num; }; MyInt *p;

Which line of the code below will cause a compiler error? int* p1,p2; int x = 3; p1 = &x; p2 = &x;

What will the following program output? class MyInt { public: int num; }; int main() { MyInt *p1; MyInt *p2; p1->num = 10; p1 = p2; cout << p1->num << " " << p2->num << endl; return 0; }

What is wrong with the following code fragment? double *dArray = new double[100]; // Code here to use array delete dArray;

Which of the following is not a valid way to dereference pointer p to access the num field?
class MyInt { public: int num; }; MyInt *p;

Which line of the code below will cause a compiler error?
int* p1,p2; int x = 3; p1 = &x; p2 = &x;

What will the following program output?
class MyInt { public: int num; }; int main() { MyInt p1; MyInt p2; p1->num = 10; p1 = p2; cout << p1->num << " " << p2->num << endl; return 0; }

What is wrong with the following code fragment?
double *dArray = new double[100]; // Code here to use array delete dArray;