Call stack behavior - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the call stack in C programming?

The call stack is a special area in memory that stores information about active function calls, including local variables, return addresses, and parameters. It helps the program keep track of where to return after a function finishes.

beginner

What happens to the call stack when a function is called?

When a function is called, a new stack frame is pushed onto the call stack. This frame contains the function's parameters, local variables, and the return address to continue after the function finishes.

beginner

What is a stack frame?

A stack frame is a block of memory on the call stack that holds data for one function call, including its parameters, local variables, and return address.

beginner

What happens when a function returns in terms of the call stack?

When a function returns, its stack frame is popped off the call stack, and the program continues execution from the return address stored in that frame.

intermediate

What is a stack overflow and when can it happen?

A stack overflow happens when the call stack grows beyond its limit, usually because of too many nested function calls or infinite recursion, causing the program to crash.

What does the call stack store during program execution?

A Information about active function calls

B Global variables only

C Only the program's source code

D Output data for the user

The call stack stores information about active function calls, including local variables, parameters, and return addresses.

What happens to the call stack when a function finishes executing?

A A new stack frame is pushed

B The entire stack is cleared

C The current stack frame is popped

D Nothing changes

When a function finishes, its stack frame is popped off the call stack to return control to the caller.

Which of the following can cause a stack overflow?

A Too many nested function calls

B Using global variables

C Declaring large arrays globally

D Printing output to the console

Too many nested function calls or infinite recursion can cause the call stack to exceed its limit, causing a stack overflow.

What is stored in a stack frame?

A Only the function's name

B Function parameters, local variables, and return address

C The entire program's code

D User input data

A stack frame stores the function's parameters, local variables, and the return address.

When a function calls another function, what happens to the call stack?

A The current stack frame is removed

B The program pauses

C The stack is reset

D A new stack frame is added on top

Calling a function adds a new stack frame on top of the call stack.

Explain how the call stack manages function calls and returns in C.

Think about what happens when a function starts and ends.

Describe what causes a stack overflow and how it relates to the call stack.

Consider what happens if the call stack grows too big.

Practice

1. What does the call stack do in a C program?

easy

A. Handles input and output operations

B. Stores global variables permanently

C. Manages memory allocation for dynamic data

D. Keeps track of function calls and local variables

Solution

1. Step 1: Understand the role of the call stack

   The call stack stores information about active function calls and their local variables during program execution.

2. Step 2: Differentiate from other memory areas

   Global variables and dynamic memory are stored elsewhere, not on the call stack.

3. Final Answer:

   Keeps track of function calls and local variables -> Option D

4. Quick Check:

   Call stack = function calls + locals [OK]

Hint: Call stack tracks active functions and locals [OK]

Common Mistakes:

• Confusing call stack with heap memory
• Thinking global variables are on the stack
• Assuming call stack manages I/O

2. Which of the following is the correct way to declare a function in C that will be called and added to the call stack?

easy

A. void myFunction() { /* code */ }

B. function myFunction() { /* code */ }

C. def myFunction() { /* code */ }

D. func myFunction() { /* code */ }

Solution

1. Step 1: Identify correct C function syntax

   In C, functions are declared with a return type, name, and parentheses, e.g., void myFunction().

2. Step 2: Recognize incorrect syntax

   Keywords like function, def, or func are not valid in C.

3. Final Answer:

   void myFunction() { /* code */ } -> Option A

4. Quick Check:

   C function declaration uses return type + name [OK]

Hint: C functions start with return type, no keywords like def [OK]

Common Mistakes:

• Using Python or JavaScript keywords in C
• Omitting return type in function declaration
• Using incorrect braces or parentheses

3. What will be the output of this C program?

void func(int n) {
    if (n == 0) return;
    printf("%d ", n);
    func(n - 1);
}

int main() {
    func(3);
    return 0;
}

medium

A. 3 2 1

B. 3 2 1 0

C. 0 1 2 3

D. 1 2 3

Solution

1. Step 1: Trace the recursive calls

   The function prints the current value of n, then calls itself with n-1 until n is 0.

2. Step 2: Determine printed values

   It prints 3, then 2, then 1, then stops before printing 0.

3. Final Answer:

   3 2 1 -> Option A

4. Quick Check:

   Print before recursion = descending order [OK]

Hint: Print before recursive call means descending output [OK]

Common Mistakes:

• Assuming print happens after recursion
• Including zero in output incorrectly
• Confusing order of prints

4. Consider this code snippet:

void foo() {
    int x = 5;
    bar();
}

void bar() {
    printf("%d", x);
}

int main() {
    foo();
    return 0;
}

What is the error here?

medium

A. Missing semicolon after bar() call

B. Function foo() is missing a return type

C. Variable x is not declared in bar()'s scope

D. main() should return void

Solution

1. Step 1: Check variable scope

   Variable x is declared inside foo(), so it is local to foo() and not visible in bar().

2. Step 2: Identify the error cause

   bar() tries to print x, but x is undefined in bar(), causing a compile error.

3. Final Answer:

   Variable x is not declared in bar()'s scope -> Option C

4. Quick Check:

   Local variables are not shared across functions [OK]

Hint: Local variables can't be accessed outside their function [OK]

Common Mistakes:

• Thinking local variables are global
• Ignoring variable scope rules
• Assuming implicit variable sharing

5. Given this recursive function:

int factorial(int n) {
    if (n <= 1) return 1;
    return n * factorial(n - 1);
}

int main() {
    int result = factorial(4);
    printf("%d", result);
    return 0;
}

How many call stack frames are active at the deepest point during execution?

hard

A. 3

B. 4

C. 5

D. 1

Solution

1. Step 1: Count recursive calls for factorial(4)

   Calls happen for n=4, 3, 2, and 1 (base case triggers at n=1).

2. Step 2: Determine deepest call stack frames

   At n=1, the deepest call, there are 4 active frames: factorial(4), factorial(3), factorial(2), and factorial(1).

3. Final Answer:

   4 -> Option B

4. Quick Check:

   Number of calls = 4 frames [OK]

Hint: Count calls including base case, exclude main [OK]

Common Mistakes:

• Counting main() as a call stack frame for this question
• Off-by-one error in counting frames
• Assuming base case does not add a frame