Unix-Lab/Prgm 12(CD) at master · ritesh-29/Unix-Lab · GitHub

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%{
  #include<ctype.h>
  char str[20];
  int i;
%}
%token id
%left '+''/''*''-';

%%
E:S {infix_postfix(str);}
S:S'+'T|S'-'T
|T
T:T'*'F|T'/'F
|F
F:id|'('S')'
|;
%%

#include<stdio.h>
main()
{
   printf("Enter an identifer\n");
   yyparse();
}

yyerror()
{
   printf("Invalid\n");
}

yylex()
{
   charch='';
   while(ch!='\n')
     {
        ch=getchar();
        str[i++]=ch;
        if(isalpha(ch))return id;
          if((ch=='+'||ch=='-'||ch=='*'||ch=='/')return ch;)
          str[--i]='\0';
          return 0;
          exit(0);
     }
}

void push(char stack[],int*pop,char ch)
{
   stack[++(*top)]=ch;
}

char pop(char stack[],int* top)
{
   return(stack[top--]);
}

int perc(char ch)
{
   switch(ch)
   {
      case'/':;
      case'*':return 2;
      case'+':;
      case'-':return 1;
      case'(':return 0;
      default:return -1;
   }
}

void infix_postfix(char infix[])
{
   int top=-1,iptr=-1,stksymb,cursymb;
   push(stck,&top,'\0');
   while((cursymb=infix[++ptr])!='\0')
     {
         switch(cursymb)
           {
              case'(':push(stack,&top,cursymb);
                      break;

              case')':stksymb=pop(stack,&top);
                      while(stksymb!='(')
                        {
                           postfix[++ptr]=stksymb;
                           stksymb=pop(stack,&top);
                        }
                        break;

                        case'*':
                        case'/':
                        case'+':
                        case'-':while(prec(stack[top])>prec(cursymb))
                                postfix[++ptr]=pop(stack,&top);
                                push(stack,&top,cursymb);
                                break;

                        default:if(isalnum(cursymb)==0)
                                  {
                                     printf("Error in input\n");
                                     exit(0);
                                  }
                                  postfix[++pptr]=cursymb;
           }
     }
     while(top!=1)
     postfix[++ptr]=pop(stack,&top);
     printf("%s",postfix);
}