Pointers and References : MCQs & PYQs with Explanation

Option C

In C++, function declarations specify the return type, function name, and parameter types. Pointers use * (float* for pointer to float, char** for pointer to pointer to char, int** for pointer to pointer to int).

• The function returns a pointer to a pointer to an integer, which is written as int**.
• The first parameter is a pointer to a float, which is written as written as float*.
• The second parameter is a pointer to a pointer to a char, which is written as char**.

Combining these, the correct function declaration is int** fun(float*, char**);.

Option B

In this program, the variable number is passed to both parameters x and y, meaning both pointers refer to the same memory location. Inside the function, the statement *x = (*x) * --(*y); first decreases the value of number using the pre-decrement operator --(*y), so number becomes 29.
Then, the expression multiplies the original value by 29. Since the original value was 30, the calculation becomes 30 * 29, resulting in 870.

Option B

Here the variable a is initialized with the value 14. The statement int &b = a; creates b as a reference variable, which means b is an alias of a and both refer to the same memory location. 
When the statement b++; is executed, it increments the value stored at that memory location. Since b and a refer to the same variable, the value of a also becomes 15. Finally, cout<<a; prints the updated value of a, which is 15.

Option C

In C++, a function pointer is a pointer that stores the address of a function. It allows a program to call a function indirectly through the pointer. Consider the declaration:
int (*FPTR)(char*)

• FPTR : Name of the pointer.
• (*FPTR) : FPTR is a pointer.
• (char*) : The function pointed to by FPTR accepts one argument of type char* (pointer to character).
• int : The function returns an integer (int) value.

Therefore, FPTR is a pointer to a function that takes a character pointer (char*) as an argument and returns an integer value.

Other Examples:

Programming Example:

#include <iostream>
using namespace std;
int findLength(char *str)
{
    int count=0;
    while (*str!='\0')
    {
        count++;
        str++;
    }
    return count;
}
int main()
{
    int (*FPTR)(char*);
    FPTR=findLength;
    char mystr[]="Suraku Academy";
    cout<<"Length : "<< FPTR(mystr);
    return 0;
}
OUTPUT
Length : 14

Option C

The statement ptr = new int[4]; dynamically allocates memory for 4 integers. The valid indices for this array are 0, 1, 2, and 3.

Option C

A pointer is a special type of variable that stores the memory address of another variable instead of its value. In the given declaration:
int C, *PTR;

• C is an integer variable.
• PTR is a pointer to an integer, which means it can store the address of an integer variable.

Option D

A pointer is a special variable that stores the memory address of another variable. In the given code:
int a = 10, b = 20;
int *p = &a, *q = &b;
p = q;
Initially:

• p stores the address of a.
• q stores the address of b.

After executing the statement p = q;, the address stored in q is copied into p. As a result, both pointers store the same address, which is the address of b.
The values of a and b remain unchanged. Only the pointer p changes its target.

#include <iostream>
using namespace std;
int main()
{
    int a=10, b=20;
    int *p=&a;
    int *q=&b;
    cout<<"a = "<<a<<", b = "<< b<<endl;
    cout<<"p points to value = " <<*p<<endl;
    cout<<"q points to value = " <<*q<<endl;
    cout<<"Address stored in p = " <<p<<endl;
    cout<<"Address stored in q = " <<q<<endl;
    p=q;
    cout<<"After p = q\n";
    cout<<"a = " <<a<< ", b = " <<b<<endl;
    cout<<"p points to value = " <<*p<<endl;
    cout<<"q points to value = " <<*q<<endl;
    cout<<"Address stored in p = " <<p<<endl;
    cout<<"Address stored in q = " <<q<<endl;
    return 0;
}
OUTPUT
a = 10, b = 20
p points to value = 10
q points to value = 20
Address stored in p = 0x7ffe96a25d8c
Address stored in q = 0x7ffe96a25d88
After p = q
a = 10, b = 20
p points to value = 20
q points to value = 20
Address stored in p = 0x7ffe96a25d88
Address stored in q = 0x7ffe96a25d88

Option B

In C++, a declaration should always be read starting from the variable name and then moving outward according to the precedence of operators. Consider the declaration:
int (*p[5])();

• p : Name of the variable.
• p[5] : p is an array of 5 elements.
• (*p[5]) : Each element of the array is a pointer.
• (*p[5])() : Each pointer points to a function.
• int : Each function returns an integer (int) value.

Therefore, the declaration means, p is an array of 5 pointers to functions, where each function takes no arguments and returns an integer value.

Option B

The given program uses a pointer p and a double pointer q. The variable a is initialized with value 3. 
The pointer p stores the address of a, and the double pointer q stores the address of p. Therefore, both *p and **q give the value 3. 
The expression b=2*(**q+*p) becomes 2*(3+3), which is equal to 12.

Option B

In this program, the pointer ptr is initialized to NULL, which means it points to nothing. When we use delete ptr;. In C++, deleting a NULL pointer is safe. If the pointer is NULL, delete does nothing and does not cause any error. Therefore, the program is semantically correct, compiles without any issues, and executes successfully without crashing.

Option C

In C++, a pointer must store the address of a variable of the same data type. Means,

• int* can store the address of an int variable.
• double* can store the address of a double variable.
• char* can store the address of a char variable.

Assigning the address of one data type to a pointer of another data type is not allowed without an explicit type cast.
The given statement, 
int p;
double *fp = &p;

• p is an integer (int) variable.
• fp is a pointer to a double (double*).
• &p is of type int*, but fp expects a double*.

Since int* cannot be assigned to double*, this declaration is incorrect and results in a Compile-Time Error.