Compiler Design MCQ Quiz in தமிழ் - Objective Question with Answer for Compiler Design - இலவச PDF ஐப் பதிவிறக்கவும்

Lexical analyzer recognizes the lexemes (alphanumeric characters in a token ) and recognize the white spaces, comments, tab and ignore them.

example;

a = \* comment*/          b;

so total 4 tokens are there (a, =, b and ;)

all spaces, tabs and comments are ignored by lexical analyzer. 

when any error occur during lexical analyzer phase then lexical analyzer show the error with line number where error is occured.

and also check the longest prefix of the identifier.

So, all the options are correct.

Directed acyclic graph is a representations for single expressions.  DAG representation perform several code improving transformations on the code represented by the block. It can eliminate local common subexpression, can eliminate dead code and can reorder statements that do not depend on one another.

For the given basic block:

d = b * c

e = a + b

b = b * c

a = e – d

DAG can be constructed as :

STEP 1:

STEP 2:

STEP 3:

So, total number of nodes are 6 and total number of edges are 6.

In second production T → T * U here T is generating T*U left recursively so * is left associative.

In third production P → Q + P, Here P is generating Q + P right recursively so + is right associative.

String: pppqppqprpqp

The output is 3123

The correct answer is option 2

CONCEPT:

• Compiler, Computer software that translates source code written in a high-level language into a set of machine-language instructions that can be understood by a digital computer’s CPU.
• It scans the entire program and translates the whole of it into machine code at once.
• A Compiler always generates an intermediary object code.
• It will need further linking. Hence more memory is needed.
• Source code → Compiler → Machine code → Output
• Compilers are very large programs, with error-checking and other abilities.
• Compiler can diagnose grammatical errors only

The correct answer is option 1 and option 4.

Key Points

Lexical phase errors:

These errors are detected during the lexical analysis phase.

• Typical lexical errors are Exceeding the length of identifier or numeric constants.
• The appearance of illegal characters
• Unmatched string

Syntactic phase errors:

These errors are detected during the syntax analysis phase.  Typical syntax errors are

• Errors in structure
• Missing operator
• Misspelt keywords
• Unbalanced parenthesis

Semantic errors:

These errors are detected during the semantic analysis phase.

• Typical semantic errors are Incompatible types of operands
• Undeclared variables
• Not matching of actual arguments with the formal one

Program 1:

int main()

{

       char a[10] =”Testbook”;

       %%  / The appearance of illegal characters  leads to lexical errors.

       %%

       return 0;

}

Program 2:

int main()

{

       char a[10]  =”Testbook”;

       int p=20,q=30,r,s,s;

       if(p>q;       / Missing operator it leads to syntactic errors but no lexical errors.

       r = 20;

}

Program 3:

int main()

{

       char a[10]  =”Testbook”;

       int p=20,q=30,r,s,s;

}

Program 4:

int main()

{

       char a[10]  =”Testbook”;

       /* He*/llo /*    /The appearance of illegal characters leads to lexical errors.

       If(a!=’\0’)

       b = 10;

}

Therefore, both statements are false. Hence option 4 is correct

Concept: LR parsers in terms of their power:

CLR > LALR > SLR > LR (0)

Explanation:

I. Canonical LR is more powerful than SLR. TRUE

II. SLR is more powerful than LALR. FALSE

III. SLR is more powerful than Canonical LR. FALSE

Concept:

Take relational algebra which generates the longest subsequence.

With  T₃ we get a subsequence of 5, and T₁ we get a subsequence of only 4, T₂ we get a subsequence of only 3.

Hence, T₃ preferred over T₂ and T1

Explanation

String = 𝑏𝑏𝑎𝑎𝑐𝑎𝑏𝑐

(𝑏|𝑎)∗ = (a + b)*

𝑐? = (ϵ + c)

𝑇3: 𝑐? (𝑏|𝑎)∗𝑐

T₃ = bbaac (longest prefix match)

T3= abc

𝑇3𝑇3 = 𝑏𝑏𝑎𝑎𝑐 𝑎𝑏𝑐

Therefore option 4 is correct

Concept:

If the value of a variable is constant, then replace the variable with the constant and it must be propagated forward from the assignment point.

Explanation:

Given code:

Int x =4;

Int y = x * 2;

Int z = a[y];

Here we use the value of constant x = 4 and replace x by its value.

STEP 1: int y = 4 * 2; int z = a[y];

STEP 2: int y = 8; int z = a[y];