Typedef Questions and Answers

Q: What will be the output of the following C code? #include <stdio.h> typedef struct p { int x, y; }k = {1, 2}; int main() { p k1 = k; printf("%d\n", k1.x); }

Correct answer: Compile time errorBecause the declaration begins with typedef, the k after the closing brace is a type name, and a type name cannot be given an initialiser - = {1, 2} is meaningless there. The later p k1 = k; compounds the error by using the tag p as a type. Remove the typedef and k becomes an initialised variable.

Q: Is the following declaration acceptable? typedef long no, *ptrtono; no n; ptrtono p;

Correct answer: YesOne typedef may declare several aliases, each with its own derived type built on the same base. Here no becomes long and ptrtono becomes long *, so both subsequent declarations are valid. It is the same grammar as an ordinary declaration such as long n, *p;, with typedef changing only what the declared names mean.

Q: What will be the output of the following C code? #include <stdio.h> typedef struct student { char *a; }stu; void main() { stu s; s.a = "hi"; printf("%s", s.a); }s

Correct answer: Compile time errorThe body of the program is correct - stu is a proper alias, s.a = "hi" is a valid pointer assignment - but there is a stray s after the closing brace of main. At file scope that is a declaration with no type, which the compiler rejects. It is worth reading to the very end of a listing before answering.

Q: Which of the following is an example of static memory allocation?

Correct answer: ArrayAn array declared with a fixed size has its storage settled at compile time, in the stack frame or the data segment according to where it is declared. Nothing is requested at run time and nothing is freed.The other three are dynamic structures built from nodes obtained with malloc as they are needed. A stack and a queue can be implemented over a fixed array, but as abstract structures they grow and shrink, which is what places them on the dynamic side of the distinction.

Q: Queue data structure works on the principle of ____________

Correct answer: First In First Out (FIFO)A queue serves elements in the order they arrived: the first item added is the first removed. Insertion happens at one end, the rear, and removal at the other, the front.That is the opposite of a stack, which is last in first out and does both operations at the same end. The distinction is not merely academic - it decides which structure suits a problem, with queues natural for scheduling and buffering and stacks natural for recursion and expression evaluation.

Q: What will be the output of the following C code? #include <stdio.h> int *(*(x()))[2]; typedef int **(*ptrfoo)())[2]; int main() { ptrfoo ptr1; ptr1 = x; ptr1(); return 0; } int *(*(x()))[2] { int (*ary)[2] = malloc(sizeof * ary); return &ary; }

Correct answer: Compile time errorThe typedef line is syntactically invalid: typedef int **(*ptrfoo)())[2]; has unbalanced parentheses, the () and the [2] both trying to attach after the declarator has already been closed. Compiling it produces an error at that line before execution is ever reached, and a second error follows on the incompatible assignment ptr1 = x;.

Q: What will be the output of the following C code? #include <stdio.h> int (*(x()))[2]; typedef int (*(*ptr)())[2] ptrfoo; int main() { ptrfoo ptr1; ptr1 = x; ptr1(); return 0; } int (*(x()))[2] { int (*ary)[2] = malloc(sizeof*ary); return &ary; }

Correct answer: Compile time errorThe line typedef int (*(*ptr)())[2] ptrfoo; is malformed. A typedef declares the new name inside the declarator, in the position a variable name would occupy - here that position is already taken by ptr, so the trailing ptrfoo is a second declarator with nothing joining it. The compiler rejects the declaration before any of the rest matters.

41.

What will be the output of the following C code?

#include <stdio.h>
    typedef struct p
    {
        int x, y;
    }k = {1, 2};
    int main()
    {
        p k1 = k;
        printf("%d\n", k1.x);
    }

A.Compile time error
B.1
C.Depends on the standard

Answer: A

Correct answer: Compile time error

Because the declaration begins with typedef, the k after the closing brace is a type name, and a type name cannot be given an initialiser - = {1, 2} is meaningless there. The later p k1 = k; compounds the error by using the tag p as a type. Remove the typedef and k becomes an initialised variable.

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42.

Which of the following is an example for non linear data type?

A.Tree
B.Array
C.Linked list
D.Queue

Answer: A

A data structure is said to be linear if its elements form a sequence or a linear list. For example array, linked list, queue, stack etc. Elements in a non linear data structure do not form a sequence. For example Trees, graphs etc.

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43.

Is the following declaration acceptable?

typedef long no, *ptrtono;
no n;
ptrtono p;

A.Yes
B.NO

Answer: A

Correct answer: Yes

One typedef may declare several aliases, each with its own derived type built on the same base. Here no becomes long and ptrtono becomes long *, so both subsequent declarations are valid. It is the same grammar as an ordinary declaration such as long n, *p;, with typedef changing only what the declared names mean.

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44.

What will be the output of the following C code?

#include <stdio.h>
    typedef struct student
    {
        char *a;
    }stu;
    void main()
    {
        stu s;
        s.a = "hi";
        printf("%s", s.a);
    }s

A.Compile time error
B.Varies
C.hi
D.h

Answer: A

Correct answer: Compile time error

The body of the program is correct - stu is a proper alias, s.a = "hi" is a valid pointer assignment - but there is a stray s after the closing brace of main. At file scope that is a declaration with no type, which the compiler rejects. It is worth reading to the very end of a listing before answering.

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45.

Which of the following is an example of static memory allocation?

A.Linked list
B.Stack
C.Queue
D.Array

Answer: D

Correct answer: Array

An array declared with a fixed size has its storage settled at compile time, in the stack frame or the data segment according to where it is declared. Nothing is requested at run time and nothing is freed.

The other three are dynamic structures built from nodes obtained with malloc as they are needed. A stack and a queue can be implemented over a fixed array, but as abstract structures they grow and shrink, which is what places them on the dynamic side of the distinction.

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46.

Queue data structure works on the principle of ____________

A.Last In First Out (LIF0)
B.First In Last Out (FILO)
C.First In First Out (FIFO)
D.Last In Last Out (LILO)

Answer: C

Correct answer: First In First Out (FIFO)

A queue serves elements in the order they arrived: the first item added is the first removed. Insertion happens at one end, the rear, and removal at the other, the front.

That is the opposite of a stack, which is last in first out and does both operations at the same end. The distinction is not merely academic - it decides which structure suits a problem, with queues natural for scheduling and buffering and stacks natural for recursion and expression evaluation.

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47.

For the following “typedef” in C, pick the best statement

typedef int INT, *INTPTR, ONEDARR[10], TWODARR[10][10];

A.It will cause compile error because typedef is being used to define multiple aliases of incompatible types in the same statement.
B.“INT x” would define x of type int. Remaining part of the statement would be ignored.
C.“INT x” would define x of type int and “INTPTR y” would define pointer y of type int *. Remaining part of the statement would be ignored.
D.“INT x” would define x of type int. “INTPTR *y” would define pointer y of type int **. “ONEDARR z” would define z as array of 10 int. “TWODARR t” would define t as array of 10 by 10 int.

Answer: D

Correct answer: “INT x” would define x of type int. “INTPTR *y” would define pointer y of type int **. “ONEDARR z” would define z as array of 10 int. “TWODARR t” would define t as array of 10 by 10 int.

One typedef may carry several declarators, exactly as an ordinary declaration may, and each gets its own derived type from the same base int. So all four aliases are created. This is the same rule that makes int a, *b, c[10]; legal - typedef changes what the declared names mean, not how the declaration is parsed.

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48.

What will be the output of the following C code?

#include <stdio.h>
    int *(*(x()))[2];
    typedef int **(*ptrfoo)())[2];
    int main()
    {
        ptrfoo ptr1;
        ptr1 = x;
        ptr1();
        return 0;
    }
    int *(*(x()))[2]
    {
        int (*ary)[2] = malloc(sizeof * ary);
        return &ary;
    }

A.Compile time error
B.Nothing
C.Undefined behaviour
D.Depends on the standard

Answer: B

Correct answer: Compile time error

The typedef line is syntactically invalid: typedef int **(*ptrfoo)())[2]; has unbalanced parentheses, the () and the [2] both trying to attach after the declarator has already been closed. Compiling it produces an error at that line before execution is ever reached, and a second error follows on the incompatible assignment ptr1 = x;.

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49.

What will be the output of the following C code?

#include <stdio.h>
    int (*(x()))[2];
    typedef int (*(*ptr)())[2] ptrfoo;
    int main()
    {
        ptrfoo ptr1;
        ptr1 = x;
        ptr1();
        return 0;
    }
    int (*(x()))[2]
    {
        int (*ary)[2] = malloc(sizeof*ary);
        return &ary;
    }

A.Compile time error
B.Nothing
C.Undefined behaviour
D.Depends on the standard

Answer: A

Correct answer: Compile time error

The line typedef int (*(*ptr)())[2] ptrfoo; is malformed. A typedef declares the new name inside the declarator, in the position a variable name would occupy - here that position is already taken by ptr, so the trailing ptrfoo is a second declarator with nothing joining it. The compiler rejects the declaration before any of the rest matters.

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50.

typedef int (*PFI)(char *, char *)creates:

A.type PFI, for pointer to function (of two char * arguments) returning int
B.Error
C.type PFI, function (of two char * arguments) returning int
D.type PFI, for pointer

Answer: A

Correct answer: type PFI, for pointer to function (of two char * arguments) returning int

The parentheses around *PFI bind the asterisk to the name before the function parameter list is applied, so the name is a pointer first and a pointer to a function second. Such aliases are the standard way of making callback tables readable: PFI compare; is a good deal clearer than writing the full declarator each time.

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