Postfix Evaluation(Single or Multi Digit) using STACK in C

POSTFIX EVALUATION WITH SINGLE OR MULTI DIGIT:

Students find difficulties in finding the correct code for Postfix evaluation using Stack which works for Single as well for multidigit also;

So here is the Question Format Given::-

Question_2; Data_Structure:

 Write a C program to evaluate the following POSTFIX expression. Use STACK to solve this problem. 

• INPUT: 5 6 2 + * 12 4 / - 
• OUTPUT: 37

Basic Understanding:

Here is the Correct code:

	#include <stdio.h>
	#include <ctype.h>
	#define SIZE 50
	int s[SIZE];
	int top=-1;
	int flag=0;
	int pop()
	{
	return(s[top--]);
	}
	int push(int elem)
	{
	if(flag==1){
	int num;
	num=pop();
	s[++top]=elem+10*num;
	}
	else if(flag==0){
	s[++top]=elem;
	flag=1;
	}
	}
	int main()
	{
	char pofx[50],ch;
	int i=0,op1,op2;
	printf("Enter the Postfix Expression:");
	fgets(pofx,100,stdin);
	while( (ch=pofx[i++]) != '\n')
	{
	if(isdigit(ch)) push(ch-'0');
	else if(ch==' ')
	flag=0;
	else
	{
	flag=0;
	op2=pop();
	op1=pop();
	switch(ch)
	{
	case '+':push(op1+op2);break;
	case '-':push(op1-op2);break;
	case '*':push(op1*op2);break;
	case '/':push(op1/op2);break;
	default:
	printf("Input invalid ... give proper input\n");
	return 0;
	}
	}
	}
	printf("Result: %d\n",s[top]);
	}

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