Control flow

ACompressed recap

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if/else choose by any non-zero condition; an else pairs with the nearest unmatched if; braces decide what belongs to a branch. switch jumps to the matching integer-constant case (or default) and falls through until break.

Loops: while tests first, do-while tests last (at least one run), for (init; test; update) is a packaged while. break leaves the innermost loop; continue skips to the update (for) or the test (while). Count iterations with the step formula, ⌊log₂ n⌋ + 1 for doubling counters, and the Phase 0 series for nested loops.

BMerged rule card

1.2.1 if / else if / else; nested conditions; switch and fall-through

• if (cond) S1; else S2; — cond non-zero → S1.
• Braces group statements; without them one statement belongs to the if.
• else ladder: first true branch runs, rest skipped.
• Dangling else binds to the nearest unmatched if.
• switch: evaluate once, jump to matching case/default, run down until break or }.
• Case labels: distinct integer constants (chars allowed).
• if (x = 5) assigns; compare with ==.

1.2.2 for, while, do-while; break and continue; tracing loop output and counting iterations

• while: test then body; do-while: body then test (≥ 1 run); for (init; test; update).
• for ≡ init; while (test) { body; update; }
• break leaves the innermost loop/switch; continue skips to update (for) or test (while).
• i = a..b−1 step s: ⌈(b − a)/s⌉ runs; i *= 2 up to n: ⌊log₂ n⌋ + 1 runs.
• Nested dependent loops: add the series (n(n + 1)/2, 2ᵏ⁺¹ − 1 …).
• Stray ; after for/while = empty body; while (n--) ends with n = −1.

CInterleaved GATE-style questions

Q1MCQ1 markOutput

What does this print?

int i, j;
for (i = 0, j = 10; i < j; i += 2, j -= 3)
    printf("(%d,%d) ", i, j);
printf("\n");

• (A) (0,10) (2,7)
• (B) (0,10) (2,7) (4,4)
• (C) (0,10) (2,7) (4,4) (6,1)
• (D) (0,10)

Q2NAT1 markIterations

How many times does the body of for (i = 3; i < 40; i += 5) run?

Numerical answer: ________

Q3MCQ2 marksOutput

What does this print?

int k = 10;
do {
    printf("%d ", k);
    k++;
} while (k < 5);
printf("| k = %d\n", k);

• (A) 10 11 12 13 14 | k = 15
• (B) nothing; the loop never runs
• (C) | k = 10
• (D) 10 | k = 11

Q4MCQ1 markif

What is printed by int x = 0; if (x == 0); printf("A"); printf("B\n");?

• (A) AB
• (B) B
• (C) A
• (D) nothing

Q5NAT2 marksSwitch

With int n = 3, s = 0; what is s after switch (n) { case 1: s += 1; case 3: s += 3; case 5: s += 5; break; default: s += 100; }?

Numerical answer: ________

Q6NAT2 marksNested loops

How many times does the innermost statement run in for (i = 1; i <= 10; i++) for (j = 1; j <= 10; j++) if (j >= i) count++;?

Numerical answer: ________

Q7MCQ1 markbreak

In a for loop nested inside another for loop, a break in the inner loop:

• (A) skips to the next inner iteration
• (B) ends both loops
• (C) ends the program
• (D) ends only the inner loop

Q8MCQ2 marksOutput

What does this print?

int i;
for (i = 1; i <= 10; i++) {
    if (i % 3 == 0) continue;
    if (i == 8) break;
    printf("%d ", i);
}
printf("\n");

• (A) 1 2 4 5 7
• (B) 1 2 4 5 7 8
• (C) 1 2 4 5 7 10
• (D) 1 2 3 4 5 6 7

Q9MSQ2 marksControl flow

Which are true?

• (A) In a while loop, continue jumps straight to the condition test.
• (B) An else pairs with the nearest unmatched if.
• (C) A switch with no matching case and no default runs no statements.
• (D) case x: where x is an int variable is allowed.

DAnswer Vault