GATE 2026 CS2 Q.35: solution and answer

GATE 2026 · CS2Q.35 · 1 mark · NAT

A lexical analyzer uses the following token definitions

$l e tt er \to [A - Z a - z]$
$d i g i t \to [0 - 9]$
$i d \to l e tt er (l e tt er ∣ d i g i t)^{*}$
$n u mb er \to d i g i t^{+}$
$w s \to (b l ank ∣ t ab ∣ n e w l in e)^{+}$

For the string given below,

x1 23mm 78 y 7z zz5 14A 8H AaYcD

the number of tokens (excluding $w s$ ) that will be produced by the lexical analyzer is ______. (answer in integer)

See the question in the paper

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Answer and solution

ANSWER

The lexical analyzer produces 13 tokens, excluding white space.

Official answer: 13Source: Official answer key, GATE 2026 CS2 (IIT Guwahati)

The analyzer always takes the longest match from the current position. An $i d$ must start with a letter and may then continue with letters or digits. A $n u mb er$ is a run of digits only.
White space is skipped, because $w s$ is excluded from the count. Split the string at the blanks: x1, 23mm, 78, y, 7z, zz5, 14A, 8H, AaYcD.
x1 begins with a letter, so the whole of it is one $i d$ . Tokens: 1.
23mm begins with a digit, so it cannot be an $i d$ . The longest $n u mb er$ is 23, because m is not a digit. Then mm is one $i d$ . Tokens: 2.
78 is one $n u mb er$ . Tokens: 1.
y is one $i d$ . Tokens: 1.
7z: the longest $n u mb er$ is 7, then z is an $i d$ . Tokens: 2.
zz5 begins with a letter, and a digit may follow inside an $i d$ , so it is one $i d$ . Tokens: 1.
14A: 14 is a $n u mb er$ , then A is an $i d$ . Tokens: 2.
8H: 8 is a $n u mb er$ , then H is an $i d$ . Tokens: 2.
AaYcD is all letters, so it is one $i d$ . Tokens: 1.
Total: $1 + 2 + 1 + 1 + 2 + 1 + 2 + 2 + 1 = 13$ .

KEY IDEA

A lexer takes the longest match at each position. An identifier must start with a letter, while a number is digits only, so a lexeme that starts with a digit splits where the digits end.

WATCH OUT FOR

Treating a lexeme such as 23mm or 7z as a single token. An $i d$ cannot start with a digit, so each of these splits into a $n u mb er$ followed by an $i d$ . Another slip is splitting zz5 into two tokens, when a digit is allowed inside an $i d$ after its first letter.

From the GATE 2026 CS2 paper. Every question of this paper · Download the full paper · All 8 Lexical analysis questions, with notes

GATE 2026 CS2 Q.35: solution and answer

Answer and solution

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