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// C Program : Infix to Prefix Conversion
#include <stdio.h>
#include <string.h>
#include <ctype.h>

#define SIZE 100

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

void push(char c)
{
    stack[++top] = c;
}

char pop()
{
    return stack[top--];
}

int precedence(char c)
{
    if (c == '^')
        return 3;
    if (c == '*' || c == '/')
        return 2;
    if (c == '+' || c == '-')
        return 1;
    return 0;
}

// Function to reverse a string
void reverse(char str[])
{
    int i, j;
    char temp;
    for (i = 0, j = strlen(str) - 1; i < j; i++, j--)
    {
        temp = str[i];
        str[i] = str[j];
        str[j] = temp;
    }
}

// Convert infix to postfix (helper function)
void infixToPostfix(char infix[], char postfix[])
{
    int i, k = 0;
    char ch;

    for (i = 0; infix[i] != '\0'; i++)
    {
        ch = infix[i];

        if (isalnum(ch))
        { // operand
            postfix[k++] = ch;
        }
        else if (ch == '(')
        {
            push(ch);
        }
        else if (ch == ')')
        {
            while (top != -1 && stack[top] != '(')
                postfix[k++] = pop();
            pop(); // remove '('
        }
        else
        { // operator
            while (top != -1 && precedence(stack[top]) >= precedence(ch))
                postfix[k++] = pop();
            push(ch);
        }
    }

    while (top != -1)
        postfix[k++] = pop();

    postfix[k] = '\0';
}

// Infix to Prefix conversion
void infixToPrefix(char infix[], char prefix[])
{
    char postfix[SIZE];

    // Step 1: Reverse infix
    reverse(infix);

    // Step 2: Replace '(' with ')' and vice versa
    for (int i = 0; infix[i] != '\0'; i++)
    {
        if (infix[i] == '(')
            infix[i] = ')';
        else if (infix[i] == ')')
            infix[i] = '(';
    }

    // Step 3: Convert to postfix
    infixToPostfix(infix, postfix);

    // Step 4: Reverse postfix -> prefix
    reverse(postfix);
    strcpy(prefix, postfix);
}

int main()
{
    char infix[SIZE], prefix[SIZE];
    printf("Enter an infix expression: ");
    scanf("%s", infix);

    infixToPrefix(infix, prefix);
    printf("Prefix Expression: %s\n", prefix);

    return 0;
}