Functions

ACompressed recap

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A function is defined once (type name(params) { … }), declared before use with a prototype, and called with arguments whose values are copied into the parameters (call by value). return ends it and hands back one value.

Scope is where a name is visible; lifetime is when it exists. Locals live in their block and start with garbage; globals and statics live for the whole run and start at 0; a static local keeps its value between calls; inner declarations shadow outer ones; extern declares without defining.

Each call pushes a stack frame (parameters, locals, return address) on the call stack and pops it on return, last in first out.

BMerged rule card

1.3.1 Declaring, defining, calling; parameters; return values; call by value

• type name(params) { … return v; } — void when nothing is returned.
• Call: evaluate args → copy into params → run → value replaces the call.
• Prototype (declaration) before first use; definition = body.
• Call by value only: parameters are copies; caller’s variables unchanged.
• return ends the function immediately.
• Argument evaluation order is unspecified.

1.3.2 Scope vs lifetime; local, global, static, extern, register; shadowing in blocks; static local variables

• Scope = where a name is visible; lifetime = when its memory exists.
• Local/auto: block scope, born and destroyed with the block, garbage start.
• Global: file scope (extern elsewhere), whole run, starts at 0.
• static local: block scope, whole run, initialized once (0 default), keeps value.
• static global/function: this file only. extern: declaration, not definition.
• Inner declarations shadow outer ones inside their block only.
• register: hint; its address may not be taken.

1.3.3 How calls work: the call stack and stack frames

• Call stack: push a frame per call, pop on return; last in, first out.
• Frame = parameters + automatic locals + return address + saved bookkeeping.
• Locals vanish with their frame; statics/globals live outside the stack.
• Depth = frames at one moment; total calls can exceed depth.
• Too deep → stack overflow.

CInterleaved GATE-style questions

Q1MCQ2 marksStatic and global

What does this print?

int x = 1;

int f(void)
{
    static int y = 2;
    int z = 3;
    x += y;
    y *= 2;
    z++;
    return x + y + z;
}

int main(void)
{
    int a = f();
    int b = f();
    printf("%d %d %d\n", a, b, x);
    return 0;
}

• (A) 9 19 7
• (B) 11 19 7
• (C) 11 19 3
• (D) 11 15 7

Q2MCQ1 markCall by value

Which statement is true about void f(int x) { x = x + 1; } called as f(a);?

• (A) a becomes x
• (B) the program does not compile
• (C) a is unchanged
• (D) a increases by 1

Q3NAT1 markStatic

A function contains static int n = 3; n += 2; return n;. What does its fourth call return?

Numerical answer: ________

Q4MCQ2 marksShadowing

What does this print?

int x = 1;                /* global */

int main(void)
{
    printf("%d ", x);
    int x = 2;            /* local x shadows the global x */
    printf("%d ", x);
    {
        int x = 3;        /* block x shadows the local x */
        printf("%d ", x);
    }
    printf("%d\n", x);
    return 0;
}

• (A) 1 2 3 3
• (B) 1 1 3 1
• (C) 1 2 3 2
• (D) 2 2 3 2

Q5MCQ1 markStack

Which is stored in a stack frame but not in the static area?

• (A) automatic locals
• (B) global variables
• (C) static locals
• (D) string literals

Q6NAT2 marksOutput

What does this print?

int h(int a, int b)
{
    return a * 10 + b;
}

int main(void)
{
    printf("%d\n", h(h(1, 2), h(3, 4)));
    return 0;
}

Numerical answer: ________

Q7MSQ2 marksScope and lifetime

Which are correct?

• (A) A global variable can be used in a function defined above its declaration without any extra declaration.
• (B) Two functions can each have a local variable named i without conflict.
• (C) extern int k; tells the compiler k is defined somewhere else.
• (D) A parameter is a local variable of its function.

Q8NAT1 markDepth

main calls a; a calls b twice; b calls c once. Counting main, what is the maximum number of frames on the stack at once?

Numerical answer: ________

Q9MCQ1 markOrder

What does this print?

void c(void) { printf("c "); }
void b(void) { printf("b1 "); c(); printf("b2 "); }
void a(void) { printf("a1 "); b(); printf("a2 "); }

int main(void)
{
    a();
    printf("\n");
    return 0;
}

• (A) a1 b1 c b2 a2
• (B) c b1 b2 a1 a2
• (C) a1 b1 b2 c a2
• (D) a1 a2 b1 b2 c

DAnswer Vault