Data and expressions

ACompressed recap

🧾

Every value has a type with a size (here char 1, short 2, int 4, long 4, long long 8, float 4, double 8 bytes) and a range (n bits: unsigned 0 … 2ⁿ − 1, signed −2ⁿ⁻¹ … 2ⁿ⁻¹ − 1). Constants have types too; a leading 0 means octal.

Operators: integer / truncates towards 0 and % follows the left sign; comparisons and logic give 1/0; && and || short-circuit; bitwise operators work on bits; x++ gives the old value, ++x the new. Precedence and associativity fix the grouping; changing a variable twice in one expression is undefined behavior.

Conversions: small integers promote to int; mixed types move towards the wider type, and signed meets unsigned as unsigned; assignment truncates fractions; casts convert on purpose; unsigned values wrap; printf returns the number of characters it printed.

BMerged rule card

1.1.1 Data types and their sizes; signed vs unsigned; constants; variables; declaration vs definition

• Sizes here: char 1, short 2, int 4, long 4, long long 8, float 4, double 8; only char = 1 is guaranteed.
• n bits: unsigned 0 … 2ⁿ − 1; signed −2ⁿ⁻¹ … 2ⁿ⁻¹ − 1.
• sizeof = size in bytes, an operator; print with %u (or %zu).
• Literals: 42, 42u, 42L, 3.75 (double), 3.75f, 'A' = 65, 0x.. hex, 0.. octal.
• const variables cannot be assigned again.
• Declaration = name + type; definition = declaration + memory. Defined once, declared many times.

1.1.2 Operators: arithmetic, relational, logical with short-circuiting, bitwise, assignment, ++ and --; precedence and associativity; undefined behavior

• int / int truncates towards 0; a % b has the sign of a; (a/b)*b + a%b == a.
• Relational and logical results are int 1 or 0; non-zero = true.
• && and || short-circuit: right side may never run (side effects skipped).
• Bitwise: & | ^ ~ << >>; ~x = −x − 1; x<<k = x·2ᵏ; x>>k = ⌊x/2ᵏ⌋ for x ≥ 0.
• x++ old value then add; ++x add then new value.
• Precedence: unary > * / % > + − > shifts > relational > == != > & > ^ > | > && > || > ?: > = > ,
• Unary, ?: and assignment associate right to left; others left to right.
• Changing a variable twice (or change + read) in one expression without an ordering point = undefined behavior.

1.1.3 Type conversion: implicit promotion, casting, overflow, char as a small integer; what printf returns

• char/short → int in arithmetic (integer promotion).
• Mixed types: convert towards double; same-size signed + unsigned → unsigned.
• double → int drops the fraction (towards 0); big int → char keeps low 8 bits.
• Cast (type)e converts e only: (double)a/b ≠ (double)(a/b).
• Unsigned wraps mod 2ⁿ; signed overflow is undefined.
• char arithmetic: 'A' = 65, 'a' = 97, '0' = 48; 'd' − '0' = digit value.
• printf returns characters printed; sizeof does not evaluate its operand; never compare fractions with ==.

CInterleaved GATE-style questions

Q1MCQ1 markOutput

What does this print?

int a, b, c;
a = b = c = 7;
a += 3;
b *= a - 5;
c %= 4;
printf("%d %d %d\n", a, b, c);

• (A) 10 35 3
• (B) 10 35 7
• (C) 10 21 3
• (D) 3 35 3

Q2NAT1 markRanges

What is the smallest value of a signed 8-bit char?

Numerical answer: ________

Q3MCQ2 marksOutput

What does this print?

int a = 4, b = 9;
int big = a > b ? a : b;
int k = (a = 1, a + 10);
printf("%d %d %d\n", big, k, a);

• (A) 9 14 4
• (B) 4 11 1
• (C) 9 2 1
• (D) 9 11 1

Q4MCQ1 markConversion

What is the value of (double)(5 / 2)?

• (A) 2.5
• (B) 3.0
• (C) 2
• (D) 2.0

Q5NAT2 marksBitwise

What is (5 << 2) ^ 3?

Numerical answer: ________

Q6MSQ2 marksUndefined behavior

With int i = 2;, which statements have undefined behavior?

• (A) i = i++ + 1;
• (B) int j = i++ + i++;
• (C) i = (i++, i + 1);
• (D) i += 2;

Q7MCQ2 marksOutput

What does this print?

char c = 200;
printf("%d\n", c);

• (A) -200
• (B) -56
• (C) 56
• (D) 200

Q8NAT1 markCharacters

What is the value of '9' - '0' + 'C' - 'A'?

Numerical answer: ________

Q9MCQ1 markShort-circuit

After int a = 1, b = 1; int r = a || ++b;, what are r and b?

• (A) r = 1, b = 1
• (B) r = 1, b = 2
• (C) r = 0, b = 1
• (D) r = 2, b = 2

Q10MCQ2 marksprintf

What does this print?

int n = printf("%d", 100);
printf(" %d\n", n);

• (A) 100 100
• (B) 3 100
• (C) 100 4
• (D) 100 3

DAnswer Vault