Data Structure lab

#include 
#include 
#include 

#define MAX 100

int stack[MAX], top = -1;

// Stack operations
void push(int val) { stack[++top] = val; }
int pop() { return (top == -1) ? 0 : stack[top--]; }

// (a) Evaluate Postfix Expression
int evaluatePostfix(char* exp) {
    int i = 0, a, b;
    char ch;
    while ((ch = exp[i++]) != '\0') {
        if (isdigit(ch)) {
            push(ch - '0');  // convert char to int
        } else {
            b = pop();
            a = pop();
            switch (ch) {
                case '+': push(a + b); break;
                case '-': push(a - b); break;
                case '*': push(a * b); break;
                case '/': push(a / b); break;
                case '%': push(a % b); break;
                case '^': push((int)pow(a, b)); break;
                default: printf("Invalid operator: %c\n", ch);
            }
        }
    }
    return pop();
}

// (b) Tower of Hanoi
void towerOfHanoi(int n, char from, char aux, char to) {
    if (n == 1) {
        printf("Move disk 1 from %c to %c\n", from, to);
        return;
    }
    towerOfHanoi(n - 1, from, to, aux);
    printf("Move disk %d from %c to %c\n", n, from, to);
    towerOfHanoi(n - 1, aux, from, to);
}

// Main Menu
int main() {
    int choice, result, n;
    char expr[100];

    do {
        printf("\n--- Stack Applications ---\n");
        printf("1. Evaluate Postfix Expression\n");
        printf("2. Tower of Hanoi\n");
        printf("3. Exit\n");
        printf("Enter your choice: ");
        scanf("%d", &choice);
        getchar(); // consume newline

        switch (choice) {
            case 1:
                printf("Enter postfix expression (e.g. 23*54*+9-): ");
                scanf("%s", expr);
                top = -1; // reset stack
                result = evaluatePostfix(expr);
                printf("Result = %d\n", result);
                break;

            case 2:
                printf("Enter number of disks: ");
                scanf("%d", &n);
                printf("Steps to solve Tower of Hanoi:\n");
                towerOfHanoi(n, 'A', 'B', 'C');
                break;

            case 3:
                printf("Exiting program.\n");
                break;

            default:
                printf("Invalid choice!\n");
        }

    } while (choice != 3);

    return 0;
}



               


  

--- Stack Applications ---

1. Evaluate Postfix Expression
2. Tower of Hanoi
3. Exit
Enter your choice: 1
Enter postfix expression : 623+-382/+*2+
Result = 9

--- Stack Applications ---

1. Evaluate Postfix Expression
2. Tower of Hanoi
3. Exit
Enter your choice: 2
Enter number of disks: 3
Steps to solve Tower of Hanoi:
Move disk 1 from A to C
Move disk 2 from A to B
Move disk 1 from C to B
Move disk 3 from A to C
Move disk 1 from B to A
Move disk 2 from B to C
Move disk 1 from A to C

--- Stack Applications ---

1. Evaluate Postfix Expression
2. Tower of Hanoi
3. Exit
Enter your choice: 3
Exiting program.