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Arrays

Question 1 CORRECT

Predict the output of below program:

#include <stdio.h>   int main() {     int arr[5];           // Assume that base address of arr is 2000 and size of integer         // is 32 bit     arr++;     printf("%u", arr);           return 0; }

A	2002
B	2004
C	2020
	lvalue required

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Question 1 Explanation: 

Array name in C is implemented by a constant pointer. It is not possible to apply increment and decrement on constant types.

Question 2 CORRECT

Predict the output of below program:

#include <stdio.h>   int main() {     int arr[5];     // Assume base address of arr is 2000 and size of integer is 32 bit     printf("%u %u", arr + 1, &arr + 1);       return 0; }

	2004 2020
B	2004 2004
C	2004 Garbage value
D	The program fails to compile because Address-of operator cannot be used with array name

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Question 2 Explanation: 

Name of array in C gives the address(except in sizeof operator) of the first element. Adding 1 to this address gives the address plus the sizeof type the array has. Applying theAddress-of operator before the array name gives the address of the whole array. Adding 1 to this address gives the address plus the sizeof whole array.

Question 3 WRONG

What is output?

# include <stdio.h>   void print(int arr[]) {    int n = sizeof(arr)/sizeof(arr[0]);    int i;    for (i = 0; i < n; i++)       printf("%d ", arr[i]); }   int main() {    int arr[] = {1, 2, 3, 4, 5, 6, 7, 8};    print(arr);    return 0; }

	1, 2, 3, 4, 5, 6, 7, 8
B	Compiler Error
	1
D	Run Time Error

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Question 3 Explanation: 

See http://www.geeksforgeeks.org/using-sizof-operator-with-array-paratmeters/ for explanation.

Question 4 CORRECT

Output of following program?

#include<stdio.h>     int main() {   int a[] = {1, 2, 3, 4, 5, 6};   int *ptr = (int*)(&a+1);   printf("%d ", *(ptr-1) );   return 0; }

A	1
B	2
	6
D	Runtime Error

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Question 4 Explanation: 

&a is address of the whole array a[]. If we add 1 to &a, we get “base address of a[] + sizeof(a)”. And this value is typecasted to int *. So ptr points the memory just after 6 is stored. ptr is typecasted to "int *" and value of *(ptr-1) is printed. Since ptr points memory after 6, ptr – 1 points to 6.

Question 5 WRONG

Consider the following C-function in which a[n] and b[m] are two sorted integer arrays and c[n + m] be another integer array.

void xyz(int a[], int b [], int c[]) {   int i, j, k;   i = j = k = O;   while ((i<n) && (j<m))      if (a[i] < b[j]) c[k++] = a[i++];      else c[k++] = b[j++]; }

Which of the following condition(s) hold(s) after the termination of the while loop? (GATE CS 2006) (i) j < m, k = n+j-1, and a[n-1] < b[j] if i = n (ii) i < n, k = m+i-1, and b[m-1] <= a[i] if j = m

A	only (i)
	only (ii)
	either (i) or (ii) but not both
D	neither (i) nor (ii)

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Question 5 Explanation: 

The function xyz() is similar to merge() of mergeSort(). The condition (i) is true if the last inserted element in c[] is from a[] and condition (ii) is true if the last inserted element is from b[].

Question 6 WRONG

Assume the following C variable declaration

int *A [10], B[10][10];

Of the following expressions I A[2] II A[2][3] III B[1] IV B[2][3] which will not give compile-time errors if used as left hand sides of assignment statements in a C program (GATE CS 2003)?

	I, II, and IV only
	II, III, and IV only
C	II and IV only
D	IV only

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Question 6 Explanation: 

See following for explanation.

int main() 
{ 
  int *A[10], B[10][10]; 
  int C[] = {12, 11, 13, 14}; 
  
  /* No problem with below statement as A[2] is a pointer 
     and we are assigning a value to pointer */
  A[2] = C;  
  
  /* No problem with below statement also as array style indexing 
      can be done with pointers*/
  A[2][3] = 15; 
  
  /* Simple assignment to an element of a 2D array*/
  B[2][3]  = 15; 
  
  printf("%d %d", A[2][0], A[2][3]); 
  return 0;
}

Question 7 CORRECT

Consider the following declaration of a ‘two-dimensional array in C:

char a[100][100];

Assuming that the main memory is byte-addressable and that the array is stored starting from memory address 0, the address of a[40][50] is (GATE CS 2002)

A	4040
	4050
C	5040
D	5050

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Question 7 Explanation: 

Address of a[40][50] = Base address + 40*100*element_size + 50*element_size
                      = 0 + 4000*1 + 50*1
                     = 4050

Question 8 WRONG

Which of the following is true about arrays in C.

	For every type T, there can be an array of T.
	For every type T except void and function type, there can be an array of T.
C	When an array is passed to a function, C compiler creates a copy of array.
D	2D arrays are stored in column major form

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Question 8 Explanation: 

In C, we cannot have an array of void type and function types. For example, below program throws compiler error

int main()
{
    void arr[100];
}

But we can have array of void pointers and function pointers. The below program works fine.

int main()
{
    void *arr[100];
}

See examples of function pointers for details of array function pointers.

Question 9 CORRECT

Predict the output of the below program:

#include <stdio.h> #define SIZE(arr) sizeof(arr) / sizeof(*arr); void fun(int* arr, int n) {     int i;     *arr += *(arr + n - 1) += 10; }   void printArr(int* arr, int n) {     int i;     for(i = 0; i < n; ++i)         printf("%d ", arr[i]); }   int main() {     int arr[] = {10, 20, 30};     int size = SIZE(arr);     fun(arr, size);     printArr(arr, size);     return 0; }

A	20 30 40
B	20 20 40
	50 20 40
D	Compile-time error

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Question 9 Explanation: 

The crux of the question lies in the expression: *arr += *(arr + n - 1) += 10; The composite operator (here +=) has right to left associativity. First 10 is added to the last element of the array. The result is then added to the first element of the array.

Question 10 WRONG

Predict output of following program

int main() {     int i;     int arr[5] = {1};     for (i = 0; i < 5; i++)         printf("%d ", arr[i]);     return 0; }

	1 followed by four garbage values
	1 0 0 0 0
C	1 1 1 1 1
D	0 0 0 0 0

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Question 10 Explanation: 

In C/C++, if we initialize an array with fewer members, all remaining members are automatically initialized as 0. For example, the following statement initializes an array of size 1000 with values as 0.

     int arr[1000] = {0};  

Question 11 CORRECT

Does C perform array out of bound checking? What is the output of the following program?

int main() {     int i;     int arr[5] = {0};     for (i = 0; i <= 5; i++)         printf("%d ", arr[i]);     return 0; }

A	Compiler Error: Array index out of bound.
B	The always prints 0 five times followed by garbage value
C	The program always crashes.
	The program may print 0 five times followed by garbage value, or may crash if address (arr+5) is invalid.

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Question 12 WRONG

#include <stdio.h>   int main() {     int a[][] = {{1,2},{3,4}};     int i, j;     for (i = 0; i < 2; i++)         for (j = 0; j < 2; j++)             printf("%d ", a[i][j]);     return 0; }

	1 2 3 4
	Compiler Error in line " int a[][] = {{1,2},{3,4}};"
C	4 garbage values
D	4 3 2 1

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Question 12 Explanation: 

There is compilation error in the declaration " int a[][] = {{1,2},{3,4}};". Except the first dimension, every other dimension must be specified. int arr[] = {5, 6, 7, 8} //valid int arr[][5] = {}; //valid int arr[][] = {}; //invalid int arr[][10][5] = {}; //valid int arr[][][5] = {}; //invalid

Question 13 WRONG

#include<stdio.h> int main() {     int a[10][20][30] = {0};     a[5][2][1] = 2;     return 0; }

Which of the following will print the value 2 for the above code?

	printf("%d",*(((a+5)+2)+1));
B	printf("%d",***((a+5)+2)+1);
	printf("%d",*(*(*(a+5)+2)+1));
D	None of these

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Question 14 CORRECT

#include <stdio.h> int main() {     char p;     char buf[10] = {1, 2, 3, 4, 5, 6, 9, 8};     p = (buf + 1)[5];     printf("%d\n", p);     return 0; }

A	5
B	6
	9
D	None of the above

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Question 15 WRONG

For a C program accessing X[i][j][k], the following intermediate code is generated by a compiler. Assume that the size of an integer is 32 bits and the size of a character is 8 bits.

  t0 = i ∗ 1024
  t1 = j ∗ 32
  t2 = k ∗ 4
  t3 = t1 + t0
  t4 = t3 + t2
  t5 = X[t4] 

Which one of the following statements about the source code for the C program is CORRECT?

	X is declared as “int X[32][32][8]”.
	X is declared as “int X[4][1024][32]”.
C	X is declared as “char X[4][32][8]”.
D	X is declared as “char X[32][16][2]”.

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Question 15 Explanation: 

The final expression can be simplified in form ofi, j and k by following the intermediate code steps in reverse order

t5 = X[t4]
   = X[t3 + t2]
   = X[t1 + t0 + t2]
   = X[i*1024 + j*32 + k*4]
   = X + i*1024 + j*32 + k*4 

Since k is multiplied by 4, the array must be an int array. We are left with 2 choices (A and B) among the 4 given choices. X[i][j][k]'th element in one dimensional array is equivalent to X[i*j*k + j*k + k]'th element in one dimensional array (Note that multi-dimensional arrays are stored in row major order in C). So we get following equations

j*k*4 = j*32, we get k = 8
i*1024 = i*j*k*4, we get j = 1024/32 = 32

Therefore option A is the only correct option as j and k are 32 and 8 only in option A.