This code is a program that evaluates a given postfix...

December 7, 2023 at 09:37 PM

include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <string.h>

struct StackNode {
    int data;
    struct StackNode* next;
};

struct StackNode* newNode(int data) {
    struct StackNode* stackNode = (struct StackNode*)malloc(sizeof(struct StackNode));
    stackNode->data = data;
    stackNode->next = NULL;
    return stackNode;
}

int isEmpty(struct StackNode* root) {
    return !root;
}

void push(struct StackNode** root, int data) {
    struct StackNode* stackNode = newNode(data);
    stackNode->next = *root;
    *root = stackNode;
}

int pop(struct StackNode** root) {
    if (isEmpty(*root)) {
        printf("Stack underflow\n");
        return -1;
    }
    struct StackNode* temp = *root;
    *root = (*root)->next;
    int popped = temp->data;
    free(temp);
    return popped;
}

int evaluatePostfix(char* expression) {
    struct StackNode* stack = NULL;
    int length = strlen(expression);
    int i;

    for (i = 0; i < length; i++) {
        if (isdigit(expression[i])) {
            push(&stack, expression[i] - '0');
        } else {
            int operand2 = pop(&stack);
            int operand1 = pop(&stack);
            switch (expression[i]) {
                case '+':
                    push(&stack, operand1 + operand2);
                    break;
                case '-':
                    push(&stack, operand1 - operand2);
                    break;
                case '*':
                    push(&stack, operand1 * operand2);
                    break;
                case '/':
                    push(&stack, operand1 / operand2);
                    break;
            }
        }
    }

    return pop(&stack);
}

int main() {
    char postfixExpression[50];
    printf("\nEnter postfix expression: ");
    scanf("%s", &postfixExpression);
    int result = evaluatePostfix(postfixExpression);
    printf("Result of postfix expression evaluation: %d\n", result);
    return 0;
}

This code is a program that evaluates a given postfix expression. It defines a stack data structure using a linked list implementation and provides functions to perform stack operations like push, pop, and check if the stack is empty.

The evaluatePostfix function takes a postfix expression as input and evaluates it using the stack. It iterates through each character in the expression and performs the following steps:

If the character is a digit, it converts it to an integer and pushes it onto the stack.
If the character is an operator (+, -, *, /), it pops the top two elements from the stack, performs the corresponding operation, and pushes the result back onto the stack.

The main function prompts the user to enter a postfix expression, calls the evaluatePostfix function to evaluate it, and prints the result.

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