#include "expeval.h"

void InfixToPostfix(char *infixstr, char *postfixstr) {
	stack *top = NULL;
	char *p = infixstr, *p2 = postfixstr, temp;
	strcat(infixstr,")");
	push(&top, '(');

	while(*p != '\0'){
		if(*p == '('){
			push(&top, *p);
		} else if (isdigit(*p) || isalpha(*p)){
			*p2 = *p;
			p2++;
		} else if (*p == ')'){
			temp = peek(top);
			pop(&top);
			while(temp != '('){
				*p2 = temp;
				p2++;
				temp = peek(top);
				pop(&top);
			}
		} else if (isoper(*p)){
			temp = peek(top);
			pop(&top);
			while(isoper(temp) && getPriority(temp) > getPriority(*p)){
				*p2 = temp;
				p2++;
				temp = peek(top);
				pop(&top);
			}
			push(&top, temp);
			push(&top, *p);
		}
		p++;
	}

	while(top != NULL){
		temp = peek(top);
		pop(&top);
		*p2 = temp;
		p2++;
	}
}

int evaluatePostfix(char *exp) {
	stack *top = NULL;
	char *p = exp;
	int a, b;
	strcat(exp,")");

	while(*p != '\0'){
		if(isdigit(*p) || isalpha(*p)) push(&top, *p - '0');
		else if (isoper(*p)){
			a = peek(top);
			pop(&top);
			b = peek(top);
			pop(&top);
			if(*p == '^' ){
				push(&top, pow(b,a));
			} else if (*p == '*'){
				push(&top, b * a);
			} else if (*p == '/'){
				push(&top, b / a);
			} else if (*p == '+') {
				push(&top, b + a);
			} else if (*p == '-') {
				push(&top, b - a);
			}
		}
		p++;
	}
	return peek(top);
}

int getPriority(char op) {
	if (op == '/' || op == '*' || op == '%') return 1;
	else if (op == '+' || op == '-') return 0;
	return 0;
}

//A function to act like isdigit() or isalpha() to tell is a character is an operator
int isoper(char c){
	if(c == '^' || c == '*' || c == '/' || c == '+' || c == '-') return 1;
	else return 0;
}

-------------------------------------------------------------------------------

#include "stack.h"

void push(stack **topp, int val) {
  stack *ptr = (stack *)malloc(sizeof(stack));
  ptr-> data = val;

  if (*topp == NULL) {
    ptr->next = NULL;
    *topp = ptr;
  } else {
    ptr -> next = *topp;
    *topp = ptr;
  }
}

void pop(stack **topp) {
  if (*topp == NULL) {
    printf("STACK UNDERFLOW \n");
  } else {
    stack *temp = *topp;
    *topp = temp->next;
    free(temp);
  }
}

int peek(stack *top) {
  if (top == NULL) {
    printf("STACK IS EMPTY \n");
    return -1;
  }
  else {
    return top->data;
  }
}

void clean(stack **topp) {
  node *temp, *np = *topp;
  while (np != NULL) {
    temp = np;
    np = np->next;
    free(temp);
  }
  *topp = NULL;
}