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Sunday, September 15, 2013
Design,develop and execute a program in C to execute a validpostfix expression using stack. Assume that the postfix expression isread as a single line consisting of non-negative single digit operandsand binary arithematic operators.The arithematic operators are +(add),-(subtract),*(multiply) and /(add).
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#include<stdio.h>
#include<stdlib.h>
#include<string.h>
void infix_postfix(char[],char[]);
char s[30];
int top=-1;
void push(char elem)
{
s[++top]=elem;
}
char pop()
{
return(s[top--]);
}
void main()
{
char infix[20];
char postfix[20];
clrscr();
printf("Enter a valid infix expression\n");
gets(infix);
infix_postfix(infix, postfix);
printf("The postfix expression is\n");
puts(postfix);
getch();
}
void infix_postfix(char infix[],char postfix[])
{
int j;
int i;
char symbol,x;
push('#');
j=0;
for(i=0;i<strlen(infix);i++)
{
symbol=infix[i];
switch(symbol)
{
case'(':
push(symbol);
break;
case ')':
while(s[top]!='(')
{
postfix[j++]=pop();
}
x=pop();
break;
case'/':
case'*':
case'+':
case'-': while(isp(s[top])>=icp(symbol))
{
postfix[j]=pop();
j++;
}
push(symbol);
break;
default:
postfix[j++]=symbol;
break;
}
}
while(s[top]!='#')
{
postfix[j++]=pop();
}
postfix[j]='\0';
}
int isp(char symbol)
{
switch(symbol)
{
case '/':
case '*':return (3);
case '+':
case '-':return (2);
case ')':
case '(':return (1);
case '#':return (-1);
default :return (0);
}
}
int icp(char symbol)
{
switch(symbol)
{
case'/':
case'*':return (3);
case'+':
case'-':return (2);
case'#':return (-1);
default:return (0);
}
}
------
/*Program Ends*/
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