Page 75 - DCAP605_ADVANCED_DATA_STRUCTURE_AND_ALGORITHMS

Advanced Data Structure and Algorithms

Notes
Example: To evaluate a Postfi x Expression:
ABC**/DE *+AC*-
The following steps will be executed:

Top C ** E
I. op. B I. op. B ** C D * E*D
+
II. op. A II. op. A A/(B**C) A/(B**C)

C
+
A A + C
= A/(B**C) + (D*E) – (A*C)
A/(B**C) + (D + E) A/(B**C) + ( D + E)

Lab Exercise Here is a program that implements the above idea into a program.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#define MAXC 80
double eva1(charl[]);
double pop(struct stack *);
void push(struct stack *, double);
int empty(struct stack *);
int isdigit(char);
double oper(intn double, double);
void main()
{
char expr[MAXC];
int position = 0;
whi1e((expr[position++] = getchar()) != ‘\’) ;
expr[--position] = ‘\0’;
printf(“%s%s”, “the original postfix expression is”, expr);
printf(“\n%f”, eval(expr));
}
struct stack
{
int top;
double data[MAXC];
}

70 LOVELY PROFESSIONAL UNIVERSITY