Infix string from left to right.Postfix string. If the scanned character is an operator and if the stack is empty Push the character to stack.stack is not empty, compare the precedence of the character with the element on top of the stack (topStack). If topStack has higher precedence over the scanned character Pop the stack else Push the scanned character to stack. Repeat this step as long as stack is not empty and topStack has precedence over the character.stack may have to the Postfix string.) If stack is not empty add topStack to Postfix string and Pop the stack. Repeat this step as long as stack is not empty.Postfix string.
 Stack |  Postfix String |
 Stack |  Postfix String |
 Stack |  Postfix String |
 Stack |  Postfix String |
#include<stdio.h>
#include<conio.h>
#define MAX 50
char post[MAX],in[MAX],stack[MAX];
int top=-1,toper=-1;
void insertpostfix(char x);
void insertstack(char x);
void popstack(char x);
int checkprec(char x);
void pop_all();
void main()
{
int i,j,chk,chk2;
clrscr();
printf("\nInsert an infix notation :: ");
gets(in);
stack[++toper]='(';
in[strlen(in)]=')';
printf("\nCharacter\tStack\tPostfix\n");
for(i=0;i<strlen(in);i++)
{
if(in[i]>='a' && in[i]<='z' || in[i]>='A' && in[i]<='Z' || in[i]>='0' && in[i]<='9')
{
insertpostfix(in[i]);
}
else if(in[i]=='(')
{
insertstack(in[i]);
}
else if(in[i]=='+' || in[i]=='-' || in[i]=='/' || in[i]=='*' || in[i]=='^')
{
chk=checkprec(in[i]);
chk2=checkprec(stack[toper]);
if(chk>chk2)
{
insertstack(in[i]);
}
else
{
popstack(in[i]);
}
}
else if(in[i]==')')
{
pop_all();
}
printf("\n%c\t\t",in[i]);
printf("%s",stack);
printf("\t%s",post);
}
printf("\n\nFinal Postfix Notation :: %s",post);
getch();
}
void insertpostfix(char x)
{
top++;
post[top]=x;
}
void insertstack(char x)
{
toper++;
stack[toper]=x;
}
void popstack(char x)
{
top++;
post[top]=stack[toper];
stack[toper]=x;
}
void pop_all()
{
while(stack[toper]!='(')
{
top++;
post[top]=stack[toper];
stack[toper]='\0';
toper--;
}
stack[toper]='\0';
toper--;
}
int checkprec(char x)
{
switch(x)
{
case '+':
case '-':
return 1;
case '*':
case '/':
return 2;
case '^':
return 3;
case '(':
return 0;
default:
return 0;
}
}
Published By Admin: Sachin Adi