I am given an arithmetic formula containing operators +, -, *, / and parentheses (which might or might not change the natural precedence of operators). An example would be the following one: a / b + f – (c + d) * e – a * c. and I am asked to use a stack (implemented as a linked list) in order to keep track of the operands and the operators: an example of how my program should work is the following:
- Read a, push on operand stack
- Read /, push on operator stack
- Read b, push on operand stack
- Read +: has lower precedence than / , so:
- pop 2 operands (a and b) from operand stack
- pop / from operator stack
- create subtree and push on operand stack
- operator stack is empty, so push + on it
- Read f, push on operand stack
- Read - : has same precedence as + , so:
- pop 2 operands from operand stack
- pop operator + from operator stack
- create a tree with operator + as the root and the two operands as left and right children
- push the root of the created tree back on the operand stack
- operator stack is empty, so push - on it
The problem that I have difficulty understanding is how can I distinguish the precedence of the operands!
Here is an incomplete version of the code that I wrote:
#include<stdio.h>
#include<stdlib.h>
#include<ctype.h>
typedef struct btnode Btree;
typedef struct node s_Node;
struct btnode {
char info;
Btree *left;
Btree *right;
};
struct node {
char element;
s_Node*next;
};
typedef struct{
s_Node *top_stack;
} stack_t;
int IsOperator(char c);
main () {
FILE* fp;
stack_t operands;
stack_t operators;
char c;
operands=NewStack();
operators=NewStack();
fp= fopen ("Myfile.txt", "r");
if (fp== NULL)
printf (" FILE COULD NOT BE OPENED");
else
{
c=getc(fp);
while (!feof (fp))
{
if ( c== ' ');
else
{
printf ("Here is your character: %c\n", c);
if (IsOperator (c))
Push (c, &operands);
else if ( isalpha (c))
}
c=getc(fp);
}
}
}
int IsOperator(char c)
{
switch(c)
{
case '+':
case '-':
case '/':
case '*':
return 1;
default:
return 0;
}
}
stack_t NewStack()
{
stack_t *n_stack;
n_stack=(stack_t*)malloc(sizeof(stack_t));
n_stack->top_stack=NULL;
return (*n_stack);
}
int Push(char e, stack_t *q)
{
s_Node *nn;
nn= (s_Node*)malloc(sizeof(s_Node));
if(Full(*q))
{
printf("\n\t Stack is Full !! \n\n");
return 0; // return 0 if enstack NOT successful
}
else
{
nn->element=e; // Storing the elemnt read inside the the new node
nn->next=q->top_stack; // Pointing the new node to the top of the stack
q->top_stack=nn; // Changing the top of the stack
return 1;
}
}
Thank you in advance!
