AIM:
To write a C program to evaluate the
postfix expression
ALGORITHM:
Step 1: Start the program.
Step 2: Read the
postfix expression from left to right
Step 3: If the
symbol read is an operand then push it onto the stack
Step 4: If the
operator is read POP two operands and perform arithmetic
operations if operator is
+ then result=operand 1 + operand 2
-
then result=operand 1 - operand 2
* then result=operand 1 * operand 2
/
then result=operand 1 / operand 2
Step 5: Push the
result onto the stack
Step 6: Repeat
steps 2-5 till the postfix expression is not over
Step 7: Stop the
program.
PROGRAM
#include <stdio.h>
#include <string.h>
int top = -1;
int stack[100];
/* push the given data into the stack */
void push (int data) {
stack[++top] = data;
}
/* Pop the top element from the stack */
int pop () {
int data;
if (top == -1)
return -1;
data = stack[top];
stack[top] = 0;
top--;
return (data);
}
int main()
{
char str[100];
int i, data = -1, operand1, operand2, result;
/* Get the postfix expression from the user */
printf("Enter ur postfix expression:");
fgets(str, 100, stdin);
for (i = 0; i < strlen(str); i++)
{
if (isdigit(str[i]))
{
/*
* if the i/p char is digit, parse
* character by character to get
* complete operand
*/
data = (data == -1) ? 0 : data;
data = (data * 10) + (str[i] - 48);
continue;
}
