MIT-Curricular/DS/C/Lab/Week5/InfixToPostfix.c

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

#define MAX_SIZE 100

char stack[MAX_SIZE];
int top = -1;

void push(char item)
{
    if (top >= MAX_SIZE - 1)
    {
        printf("Stack Overflow\n");
        return;
    }
    stack[++top] = item;
}

char pop()
{
    if (top < 0)
    {
        printf("Stack Underflow\n");
        return -1;
    }
    return stack[top--];
}

int precedence(char symbol)
{
    switch (symbol)
    {
    case '^':
        return 3;
    case '*':
    case '/':
        return 2;
    case '+':
    case '-':
        return 1;
    default:
        return 0;
    }
}

void infixToPostfix(char infix[], char postfix[])
{
    int i, j = 0;
    char symbol, next;
    for (i = 0; i < strlen(infix); i++)
    {
        symbol = infix[i];
        if ((symbol >= 'a' && symbol <= 'z') || (symbol >= 'A' && symbol <= 'Z') || (symbol >= '0' && symbol <= '9'))
        {
            postfix[j++] = symbol;
        }
        else if (symbol == '(')
        {
            push(symbol);
        }
        else if (symbol == ')')
        {
            while ((next = pop()) != '(')
            {
                postfix[j++] = next;
            }
        }
        else
        {
            while (top > -1 && precedence(stack[top]) >= precedence(symbol))
            {
                postfix[j++] = pop();
            }
            push(symbol);
        }
    }
    while (top > -1)
    {
        postfix[j++] = pop();
    }
    postfix[j] = '\0';
}

int main()
{
    char infix[MAX_SIZE], postfix[MAX_SIZE];
    printf("Enter infix expression: ");
    gets(infix);
    infixToPostfix(infix, postfix);
    printf("Postfix expression: %s\n", postfix);
    return 0;
}