Question

Consider the following two C code segments. Y and X are one and two dimensional arrays of size n and $n\times n$ respectively, where $2\le n\ge 10.$ Assume that in both code segments, elements of Y are initialized to 0 and each element X[i][j] of array X is initialized to i + j. Further assume that when stored in main memory all elements of X are in same main memory page frame.

Code segment 1 :
// initialize elements of Y to 0
// initialize elements X [i][j] of X to i+j
for (i =0; i < n; i++)
Y [i] + = X [0] [i];

Code segment 2 :
// initialize elements of Y to 0
// initialize elements X[i][j] of X to i+j
for (i =0; i < n; i++)
Y [i] + = X [i] [0];

Which of the following statements is/are correct?

S1 : Final contents of array Y will be same in both code segments.

S2 : Elements of array X accessed inside the for loop shown in code segment 1 are contiguous in main memory.

S3 : Elements of array X accessed inside the for loop shown in code segment 2 are contiguous in main memory.

• A. Only S1 and S3 are correct
• B. Only S3 is correct
• C. Only S1 and S2 are correct
• D. Only S2 is correct

Answer 1

The correct option is C Only S1 and S2 are correct

Y is one dimensional array

X is two dimensional array


$\begin{array}{ccccccc}0& 1& 2& 3& & \cdots & n-1\end{array}$

$\begin{array}{c}0\\ 1\\ 2\\ 3\\ \\ n-1\end{array}{\left[\begin{array}{cccccc}0& 1& 2& 3& \cdots & n-1\\ 1& 2& 3& 4& \cdots & n\\ 2& 3& 4& 5& \cdots & n+1\\ 3& 4& 5& 6& \cdots & n+2\\ \cdots & & & & & \\ n-1& n& n+1& n+2& \cdots & n+n-2\end{array}\right]}_{n\times n}$

Code segment 1 :

for (i = 0; i < n; i++)
Y[i] + = X [0] [i];

Code segment 2:

for (i = 0; i < n; i++)
Y[i] + = X [i] [0];

S1 : Final contents of array Y will be same in both code segments.


Output of both segments.

S2 : X contents are stored row wise in C- program hence code segment row '0' accessed contiguous in memory.

S3 : In code segment 2, content of X are not accessed in contiguous.