ISRO CSE 2018 PYQ ⋆ CSE Study247

Question 61

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

Consider the following declaration :

CODE

struct addr {
    char city[10];
    char street[30];
    int pin;
};

CODE

struct {
    char name [30];
    int gender;
    struct addr locate;
} person, *kd = &person;

Then *(kd -> name + 2) can be used instead of

A person.name + 2 B kd -> (name + 2) C *((*kd).name + 2) D either (a) or (b), but not (c)

📘 Solution & Detailed Explanation

🔢 Step-by-Step Solution

Detailed Breakdown

CODE

Pointer Dereferencing (-> vs .):
The variable kd is a pointer to the structure variable person (*kd = &person;).
The arrow operator (->) is syntactically a shorthand for dereferencing a pointer and then accessing a member:
\(kd\rightarrow \text{
    ame}\equiv (*kd).\text{
    ame}\)

CODE

Substituting into the Expression:
Substituting this equivalence directly into the target expression:
\(\text{*(}\mathbfit{kd\rightarrow }\text{
    ame}+2\text{)}\implies \text{*(}\mathbfit{(*kd).}\text{
    ame}+2\text{)}\)
This matches option (c) exactly.

Why other options are incorrect:

• (a) person.name + 2: The array name person.name decays to a pointer (char *). Adding 2 to it results in a memory address (char *). However, the target expression has a dereferencing asterisk * at the very front, which retrieves the actual value (char) at that index.
• (b) kd -> (name + 2): This is syntactically invalid in C because name is not a standalone variable outside the structure scope, so it cannot be grouped with + 2 inside parentheses like that.

Question 62

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

If a variable can take only integral values from 0 to n, where n is an integer, then the variable can be represented as a bit-field whose
width is ( the log in the answersare to the base 2, and [log n] means the floor of logn )

A \(\lfloor\log(n)\rfloor + 1\) bits. B floor(log2(n-1)) + 1 bits C floor(log2(n+1)) + 1 bits D None of these

📘 Detailed Solution

Step-by-Step Proof

To find the minimum number of bits needed for a bit-field, we need to determine how many bits are required to represent the maximum possible value, which is \(n\).
The number of bits required to write any positive integer \(n\) in base-2 (binary) notation is given by the standard formula:
\(\text{Width}=\lfloor \log _{2}(n)\rfloor +1\)

Verifying with a Simple Example

CODE

Let's test the formula using \(n = 3\):
• Possible Values: The variable can take any integral value from \(0\) to \(3\) (\(0, 1, 2, 3\)).
• Binary Representation:
	• \(0 = 00_2\)
	• \(1 = 01_2\)
	• \(2 = 10_2\)
	• \(3 = 11_2\)
• Actual bits needed: 2 bits are fully sufficient to represent all values up to \(3\).
Now let's plug \(n = 3\) into the options:
• Option (a): \(\lfloor\log_2(3)\rfloor + 1 = 1 + 1 = \mathbf{2\text{ bits}}\) (Correct)
• Option (c): \(\lfloor\log_2(3 + 1)\rfloor + 1 = \lfloor\log_2(4)\rfloor + 1 = 2 + 1 = 3\text{ bits}\) (Incorrectly overestimates)

Another Test (\(n = 4\))

CODE

• Possible Values: \(0, 1, 2, 3, 4\). The binary for \(4\) is \(100_{2}\), which requires 3 bits.
• Option (a): \(\lfloor\log_2(4)\rfloor + 1 = 2 + 1 = \mathbf{3\text{ bits}}\) (Correct)
Therefore, option (a) represents the exact minimum width of the bit-field.

Question 63

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

The following C program

main()
{
fork() ; fork() ; printf("yes");
}
If we execute this core segment, how manytimes the string yes will be printed?

A Only Once B 2 times C 4 times D 8 times

Question 64

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

Given √224_r = 13_r the value of radix r is

A 10 B 8 C 6 D 5

Question 65

MCQ · Single Correct 1 mark

Previous Year Question ISRO CSE 2018 PYQ

Determine the number of page faults when references to pages occur in the order - 1, 2, 4, 5, 2, 1, 2, 4. Assume that the main
memory can accommodate 3 pages and the main memory already has the pages 1 and 2, with page 1 having brought earlier than
page 2. (assume LRU algorithm is applied)

A 3 B 4 C 5 D None of the above