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

int tos = -1;
int tos2 = -1;

char input[100];
int size1 = strlen(input);

int size2 = size1+5;
char output[size2];
char operator[size2];

int result_s[100];

int k = 0;
for(k = 0 ; k < 100 ; k++)
{
    input[k] = NULL;
    result_s[k] = 0;
}
for(k = 0 ; k < size2 ; k++)
{
    output[k] = NULL;
    operator[k] = NULL;
}


int is_empty(char string[], int maximum_size)
{
    if (tos < 0 || string[0] == NULL) return 1;
    else return 0;
}

void push(char string[] , char element)
{
    tos++;
    string[tos] = element;
    return;
}

char pop(char string[])
{
    char element;
    element = array[tos];
    string[tos] = NULL;
    tos--;
    return element;
}

void infix_to_postfix(char string[])
{
    int i = 0;
    int j = 0;

    while (i != size1)
    {
        if (string[i] >= '0' && string[i] <= '9')
        {
            output[j] = string[i];
            j++;
            i++;
            continue;
        }

        else switch(string[i])
        {
            case '(':case '+': case '-': case '*': case '/':
                while ( !is_empty(operator , size2) && strchr (string[i] , "+-") != NULL && strchr(operator[tos] , "*/" != NULL) )
                    {
                        if ( strchr(operator[tos] , "(" != NULL) )    break;

                        output[j] = pop(operator);
                        j++;
                    }
                push(operator,string[i]);
                i++;
                continue;

            case ')':
                while (!isempty(operator , size2))
                {
                    output[j] = pop(operator,size2);
                    j++;

                    if ( strchr(operator[tos] , "(" != NULL) )
                    {
                        pop(operator,size2);
                        continue;
                    }
                }
        }
    }

    while (!isempty(operator , size2))
    {
        if ( strchr(operator[tos] , "(" != NULL) )    pop(operator,size2);

        else
        {
            output[j] = pop(operator,size2);
            j++;
        }
    }
}

void push_to_result(int array[], int number)
{
    tos2++;
    array[tos] = number;
    return;
}

void pop_from_result(int array[])
{
    int element;
    element = array[tos];
    array[tos] = 0;
    tos--;
    return element;
}

int evaluate_postfix(char string[])
{
    int operand1;
    int operand2;

    int temp_result = 0;

    int i = 0;

    while(i != size2)
    {
        if (string[i] >= '0' && string[i] <= '9')
        {
            push_to_result(result_s,0);
            i++;
            continue;
        }

        switch(string[i])
        {
            case '0':
                push_to_result(result_s,0);
                i++;
                continue;
            case '1':
                push_to_result(result_s,1);
                i++;
                continue;
            case '2':
                push_to_result(result_s,2);
                i++;
                continue;
            case '3':
                push_to_result(result_s,3);
                i++;
                continue;
            case '4':
                push_to_result(result_s,4);
                i++;
                continue;
            case '5':
                push_to_result(result_s,5);
                i++;
                continue;
            case '6':
                push_to_result(result_s,6);
                i++;
                continue;
            case '7':
                push_to_result(result_s,7);
                i++;
                continue;
            case '8':
                push_to_result(result_s,8);
                i++;
                continue;
            case '9':
                push_to_result(result_s,9);
                i++;
                continue;
            case '+':
                operand2 = pop_from_result(result_s);
                operand1 = pop_from_result(result_s);
                temp_result = operand1 + operand2;
                push_to_result(result_s,temp_result);
                i++;
                continue;
            case '-':
                operand2 = pop_from_result(result_s);
                operand1 = pop_from_result(result_s);
                temp_result = operand1 - operand2;
                push_to_result(result_s,temp_result);
                i++;
                continue;
            case '*':
                operand2 = pop_from_result(result_s);
                operand1 = pop_from_result(result_s);
                temp_result = operand1 * operand2;
                push_to_result(result_s,temp_result);
                i++;
                continue;
            case '/';
                operand2 = pop_from_result(result_s);
                operand1 = pop_from_result(result_s);
                temp_result = operand1 / operand2;
                push_to_result(result_s,temp_result);
                i++;
                continue;
        }
    }

    return temp_result;
}

int main()
{
    int result;

    puts("Infix to Postfix Evaluation Program :");
    puts("--------------------------------------\n");

    printf("Enter Mathematical Expression : ");
    gets(input);

    infix_to_postfix(input);

    result = evaluate_postfix(output);
    printf("\nResult = %d", result);
}