Evaluate Postfix Expression Using Stack in DSA C - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push a value onto the stack.

DSA C

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

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

Avalue

Bstack

Ctop

D*top

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'top' instead of 'value' to push.

Not incrementing the top before assignment.

We push the given value onto the stack by incrementing top and assigning value.

2fill in blank

medium

Complete the code to pop a value from the stack.

DSA C

int pop(int stack[], int *top) {
    return stack[[1]--];
}

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

A*top

Btop

Cstack

D(*top)

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'top' instead of '*top' causing wrong memory access.

Decrementing top before accessing the value.

We return the value at the current top and then decrement top.

3fill in blank

hard

Fix the error in the switch case to perform addition.

DSA C

switch (exp[i]) {
    case '+':
        res = val1 [1] val2;
        break;
    // other cases
}

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A-

B/

C+

D*

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' causing subtraction.

Using '*' or '/' causing wrong operation.

The '+' operator performs addition between val1 and val2.

4fill in blank

hard

Fill both blanks to correctly pop two values for operation.

DSA C

int val2 = pop(stack, [1]);
int val1 = pop(stack, [2]);

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Atop

B*top

C&top

Dstack

Attempts:

3 left

💡 Hint

Common Mistakes

Passing top instead of &top causing incorrect stack behavior.

Passing *top causing type mismatch.

We pass the address of top (&top) to pop to update the top index correctly.

5fill in blank

hard

Fill all three blanks to correctly evaluate the postfix expression.

DSA C

for (int i = 0; exp[i] != '\0'; i++) {
    if (isdigit(exp[i])) {
        push(stack, [1], exp[i] - '0');
    } else {
        int val2 = pop(stack, [2]);
        int val1 = pop(stack, [3]);
        // perform operation
    }
}

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

A&top

Btop

C*top

Dstack

Attempts:

3 left

💡 Hint

Common Mistakes

Passing top or *top causing incorrect stack updates.

Passing stack instead of &top causing errors.

We pass &top to push and pop so that the top index is updated correctly.