#include<stdio.h>
#include<string.h>
#define MAX 50
int stack[MAX];
char post[MAX];
int top=-1;
void pushstack(char a);
void pushstack2(char a);
void evaluate(char c);
int main()
{
    int i,l;
    printf("NOTE: Remember to inlcude SPACE (' ') between each element, but negative must be written normaly.\n");
    printf("Insert a postfix notation :: ");
    gets(post);
    l=strlen(post);
    for(i=0;i<l;i++)
    {
        if(post[i] == ' '){
            continue;
        }
        else if(post[i] == '-' && post[i+1]>='0' && post[i+1]<='9'){
            pushstack2 (post [i+1]);
            i++;
        }
        else if(post[i]>='0' && post[i]<='9')
        {
            pushstack(post[i]);
        }
        else if(post[i]=='+' || post[i]=='-' || post[i]=='*' || post[i]=='/' || post[i]=='^')
        {
            evaluate(post[i]);
        }

    }
    printf("\n\nResult = %d",stack[top]);

    return 0;
}

void pushstack2(char a)
{
    top++;
    stack[top]=(int) a - 48;
    stack[top]=-stack[top];
}

void pushstack(char a)
{
    top++;
    stack[top]=(int) a - 48;
}

void evaluate(char c)
{
    int a,b,ans;
    a=stack[top];
    stack[top]='\0';
    pop();
    top--;
    b=stack[top];
    stack[top]='\0';
    top--;
    switch(c)
    {
        case '+':
            ans=b+a;
            break;
        case '-':
            ans=b-a;
            break;
        case '*':
            ans=b*a;
            break;
        case '/':
            ans=b/a;
            break;
    }
    top++;
    stack[top]=ans;
}
void push (int elem) {
    if (top >= MAX){
        puts("Stack Full!\n");
    }
    else{
        stack [top++] = elem;
    }
}
void pop(){
    top--;
    if(top < 0){
        printf("Stack empty.");
        return -1;
    }
    else{
        return (stack[top]);
    }
}