infixtopostfix.c

#include<stdio.h>
#include<conio.h>
#include<ctype.h>
void main()
{
  int i,j=-1,top=-1;
  clrscr();
  char in[30], po[30],stack[20];
  printf("\n Enter the infix expression ");
  gets(in);
  for(i=0;in[i]!='\0';i++)
    {
       if(isalpha(in[i]))
	    {
	     po[++j]=in[i];
	     po[j+1]='\0';
	    }
       else
       switch(in[i])
       {
	 case '(' :
		   stack[++top] = in[i];stack[top+1]='\0';
		    break;
	 case '+':
	 case '-':
		   while(stack[top]!='('&&top>-1)
		   po[++j]=stack[top--];
		   stack[++top]=in[i];stack[top+1]='\0';
		   break;
	 case '*' :
	 case '/' :
		   while((stack[top]!='('&&top>-1)&&((stack[top]=='*')||(stack[top]=='/')))
		   po[++j]=stack[top--];po[j+1]='\0';
		   stack[++top]=in[i];stack[top+1]='\0';
		   break;
	case ')' :

		   while(stack[top]!='(')
		  { po[++j] = stack[top--];
		  po[j+1]='\0'; }
		  top=top-1;
       }    }

    while(top!=-1&&stack[top]!='(')
     po[++j]=stack[top--];
     po[j+1]='\0';
    printf("\n postfix expression is:");
    puts(po);
    getch();
}