Push Operation on Stack in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack.

DSA C

void push(int stack[], int *top, int value, int max_size) {
    if (*top < max_size - 1) {
        *top = *top [1] 1;
        stack[*top] = value;
    }
}

Drag options to blanks, or click blank then click option'

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' to update the top index.

Forgetting to update the top before assigning the value.

To push an element, we increase the top index by 1 before assigning the value.

2fill in blank

medium

Complete the condition to check if the stack is full before pushing.

DSA C

if (*top [1] max_size - 1) {
    // Stack is full
}

Drag options to blanks, or click blank then click option'

A==

B>

C<

D>=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' or '>=' which can cause out of bounds errors.

Using '<' which checks for not full.

The stack is full when top equals max_size - 1.

3fill in blank

hard

Fix the error in updating the top index during push.

DSA C

void push(int stack[], int *top, int value, int max_size) {
    if (*top < max_size - 1) {
        *top [1] *top + 1;
        stack[*top] = value;
    }
}

Drag options to blanks, or click blank then click option'

A=

B==

C+=

D-=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '==' which causes no change to *top.

Using '-=' which decreases top incorrectly.

Use '=' to assign the incremented value to *top, not '==' which is a comparison.

4fill in blank

hard

Fill both blanks to complete the push function with overflow check.

DSA C

void push(int stack[], int *top, int value, int max_size) {
    if (*top [1] max_size - 1) {
        printf("Stack overflow\n");
        return;
    }
    *top [2] *top + 1;
    stack[*top] = value;
}

Drag options to blanks, or click blank then click option'

A==

B<

C=

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' in overflow check which is incorrect.

Using '==' to update top instead of assignment.

Check if top equals max_size - 1 for overflow, then assign incremented top with '='.

5fill in blank

hard

Fill all three blanks to implement push with overflow check and update.

DSA C

void push(int stack[], int *top, int value, int max_size) {
    if (*top [1] max_size - 1) {
        printf("Stack overflow\n");
        return;
    }
    *top [2] *top [3] 1;
    stack[*top] = value;
}

Drag options to blanks, or click blank then click option'

A==

B+

D=

Attempts:

3 left

💡 Hint

Common Mistakes

Using '<' or '>' in overflow check.

Using '+=' instead of '=' and '+' separately.

Check overflow with '==', assign top with '=', and increment by '+ 1'.

Practice

1. What does the push operation do in a stack?

easy

A. Checks if the stack is empty

B. Adds an element to the top of the stack

C. Removes the top element from the stack

D. Returns the bottom element of the stack

Solution

1. Step 1: Understand stack operations

   A stack is a data structure where elements are added or removed from the top only.

2. Step 2: Define push operation

   The push operation adds a new element on top of the existing elements in the stack.

3. Final Answer:

   Adds an element to the top of the stack -> Option B

4. Quick Check:

   Push means add on top = C [OK]

Hint: Push always adds on top of stack [OK]

Common Mistakes:

• Confusing push with pop operation
• Thinking push removes elements
• Mixing stack with queue operations

2. Which of the following is the correct syntax to push an element 5 onto a stack named s in C?

easy

A. s.push = 5;

B. s.push(5);

C. push(5, s);

D. push(s, 5);

Solution

1. Step 1: Understand typical C stack push syntax

   In C, stack operations are usually functions where the stack is passed as the first argument.

2. Step 2: Match syntax with parameters

   The correct function call to push 5 onto stack s is push(s, 5);.

3. Final Answer:

   push(s, 5); -> Option D

4. Quick Check:

   Function push(stack, value) = A [OK]

Hint: In C, function push(stack, value) is standard [OK]

Common Mistakes:

• Using object.method syntax (not C style)
• Swapping argument order
• Assigning value instead of calling function

3. What will be the content of the stack after executing the following code?

int stack[5];
int top = -1;
// Push function
void push(int val) {
  if(top < 4) {
    top++;
    stack[top] = val;
  }
}

push(10);
push(20);
push(30);

medium

A. [10, 20, 30]

B. [30, 20, 10]

C. [10, 20]

D. Empty stack

Solution

1. Step 1: Trace each push call

   Initially, top = -1. After push(10), top=0, stack[0]=10. After push(20), top=1, stack[1]=20. After push(30), top=2, stack[2]=30.

2. Step 2: List stack content from bottom to top

   Stack elements from index 0 to top (2) are [10, 20, 30].

3. Final Answer:

   [10, 20, 30] -> Option A

4. Quick Check:

   Push adds at top increasing index = B [OK]

Hint: Stack stores pushed elements in order at increasing top index [OK]

Common Mistakes:

• Reversing order of elements
• Confusing top index with element values
• Assuming stack is empty after pushes

4. Identify the error in the following push function for a stack of size 3:

int stack[3];
int top = 0;
void push(int val) {
  if(top <= 3) {
    stack[top] = val;
    top++;
  }
}

medium

A. Condition should be top < 3, not top <= 3

B. top should be incremented before assignment

C. stack array size should be 4

D. top should start at -1, not 0

Solution

1. Step 1: Analyze top and condition

   top starts at 0, which is valid for empty stack at index 0. The condition allows top to be 3, which is out of bounds for stack[3] (indices 0 to 2).

2. Step 2: Correct the condition

   Change condition to top < 3 to prevent overflow and invalid access.

3. Final Answer:

   Condition should be top < 3, not top <= 3 -> Option A

4. Quick Check:

   Stack max index 2 means top < 3 [OK]

Hint: Check array bounds: top must be less than size [OK]

Common Mistakes:

• Allowing top to equal array size causing overflow
• Starting top at -1 but not adjusting code
• Incrementing top before assignment causing skip

5. Given a stack implemented with an array of size 4 and top = 2 currently, what will happen if we try to push two more elements without popping?
Choose the correct behavior.

hard

A. Both pushes fail immediately due to full stack

B. Both pushes succeed, stack size automatically increases

C. First push succeeds, second push causes stack overflow

D. First push causes overflow, second push is not attempted

Solution

1. Step 1: Understand current stack state

   Array size is 4, so valid indices are 0 to 3. top=2 means top element is at index 2, so one slot remains at index 3.

2. Step 2: Push two elements

   First push increments top to 3 and stores element at index 3 (valid). Second push tries to increment top to 4, which is out of bounds, causing overflow.

3. Final Answer:

   First push succeeds, second push causes stack overflow -> Option C

4. Quick Check:

   Array size 4, top max index 3, overflow after that [OK]

Hint: Stack size fixed; overflow after last index [OK]

Common Mistakes:

• Assuming stack auto-expands
• Thinking both pushes fail immediately
• Confusing top index with count