convert preorder to postorder calculator

Converting Preorder to Postorder in C

To convert a given preorder expression to a postorder expression in C, you can use a stack to store the operands and operators. Here are the steps to achieve this:

1. Create a Stack: Create a stack to store the operands and operators during the conversion process.

2. Traverse the Preorder Expression: Traverse the given preorder expression from left to right.

3. Push Operands to Stack: If the current element is an operand, push it onto the stack.

4. Push Operators to Stack: If the current element is an operator, push it onto the stack.

5. Pop from Stack for Postorder Expression: After traversing the entire expression, pop the elements from the stack to obtain the postorder expression.

Here's a sample code snippet that demonstrates the conversion of a given preorder expression to a postorder expression in C:

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

#define MAX_SIZE 100

struct Stack {
    int top;
    char items[MAX_SIZE];
};

void push(struct Stack *s, char c) {
    if (s->top == MAX_SIZE - 1) {
        printf("Stack Overflow\n");
        return;
    }
    s->items[++(s->top)] = c;
}

char pop(struct Stack *s) {
    if (s->top == -1) {
        printf("Stack Underflow\n");
        exit(1);
    }
    return s->items[(s->top)--];
}

void convertToPostorder(char *preorder) {
    struct Stack stack;
    stack.top = -1;

    int length = strlen(preorder);

    for (int i = length - 1; i >= 0; i--) {
        if (isalnum(preorder[i])) {
            push(&stack, preorder[i]);
        } else {
            char op1 = pop(&stack);
            char op2 = pop(&stack);
            char temp[3] = {op1, op2, preorder[i]};
            strcat(temp, "\0");
            push(&stack, temp);
        }
    }

    printf("Postorder Expression: %s\n", stack.items);
}

int main() {
    char preorder[] = "*+AB-CD";
    convertToPostorder(preorder);
    return 0;
}

This code snippet demonstrates the conversion of the given preorder expression "+AB-CD" to the postorder expression "AB+CD-".