Use of Polish notations in C Programming

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/* polish.c */

  # include<malloc.h>
  # include<string.h>
  # include<stdlib.h> 
  # define size 5 
          void push(char *, char , int *);
          char pop( char *, int *);
          int letter_match(char );
          void push(char *, int *, char );
          int match_number(char );
          int match_operator(char );
          int operator_precedence(char );
          void polish_fun(char *, char *, int *);
          void error(int, int );

/* Push function */

    void push( char s[], int *s_pointer, char ch)
       {
         if(*s_pointer == size)
           {
         printf("\n Stack overflow");
           }
           else
           {
         s[++(*s_pointer)] = ch ;
           }
     }

/* Pop function */

  char pop( char s[], int *s_pointer)
       {
     if(*s_pointer < 0)
      {
       printf("\n Stack underflow");
       return 0;
      }
      else
      {
       return(s[(*s_pointer) -- ]);
      }
      }

/* Definition of function */

  int letter_match(char ch)
        {
          return(((ch>='A')&&(ch<='Z')) || ((ch>='a')&&(ch <= 'z')));
        }

/* Definition of the function */

 int  match_number( char ch)
      {
         return((ch >='0') && (ch<='9'));
      }

/* Definition of the function */

  int match_operator(char ch)
      {
      int i;
        char operator[6];

          operator[0] = '+';
          operator[1] = '-';
          operator[2] = '*';
          operator[3] = '/';
          operator[4] = '%';

         for(i = 0; i < 5; i ++)
         {
            if(ch == operator[i])
              return(1);
             else
              return(0);
         }
       }

/* Definition of the function */

  int operator_precedence(char ch)
     {
       int preced;
       switch(ch)
      {
        case '(' : preced = 0; break;
        case '+' :
        case '-' : preced = 1; break;
        case '*' :
        case '/' : preced = 2; break;
        case '%' : preced = 3; break;
      }
      return(preced);
     }

/* Definition of the function */

   void polish_fun(char infix[], char suffix[], int *err)
       {
     char ch, last =')';
     char stack[size];
     int i = 0;
     int s_pointer = -1;
     int bracket = 1;
     int ifp,sfp = 0;

     push(stack, &s_pointer,'(');

       do
         {
           while(infix[i] ==' ')
           ++i;
           ifp = i;
           ch = infix[ifp];
   switch(ch)
   {
   case '(': if(letter_match(last)||match_number(last) || (last == ')'))
          {
         *err = 1;
         error(1,ifp+1);
          }
          ++bracket ;
          push(stack,&s_pointer,ch);
          break;
    case '+':
    case '-':
    case '*':
    case '/':
    case '%':

      if(match_operator(last)||(!letter_match(last)&& !match_number(last)&&(last!=')')))
     {
       *err = 1;
       error(2,ifp+1);
     }

     while(operator_precedence(stack[s_pointer] >=operator_precedence(ch))
       suffix[sfp++]=pop(stack,&s_pointer);
       push(stack,&s_pointer,ch);
       break;

    case ')':
      if(match_operator(last)
    { *err = 1;
       error(2,ifp+1);
    }

    if(last == '(')
       {
          *err = 1;
          error(2,ifp+1);
          error(1,ifp+1);
       }

    while(stack[s_pointer] != '(' && s_pointer > 0)
      suffix[sfp++] = pop(stack, &s_pointer);
      --s_pointer;
      --bracket;
      break;

    case  ' ': while(infix[ifp+1] == ' ' && !infix[ifp])
         ++ifp;
         break;
    default:
          if(letter_match(last)||math_number(last))
           {
          *err = 1;
          error(1,ifp+1);
          error(5,ifp+1);
           }

           if (letter_match(ch))
          suffix[sfp++] = infix[ifp];
          else
           if (match_number(ch))
             {
               while(match_number(infix[ifp]))
              suffix[sfp++] = infix[ifp++];
              --ifp;
              }

              else error(4,ifp+1);
           } /* end of switch */

    last = infix[ifp];
    ++ifp;
    i = ifp;
    } while(infix[ifp]);

    suffix[sfp] = 0;
    if(bracket)
      {
         *err =1;
         error(3,ifp-1);
       }
    }
    break;

/* Definition of the function */

    void input(char infix[])
       {
         int i = 0;
         printf("\nInput the infix expression: ");
         gets(infix);
         i = strlen(infix);
         printf("\n Entered expression is :");
         gets(infix);
         infix[i] = ')';
         infix[i+1] = '\0';
        }

 /* Definition of the function */

 void error(int n, int ifp)
    {
       switch(n)
       {
         case 1: printf("\n Error->1:Missing operator");
         case 2: printf("\n Error->2:Missing operand");
         case 3: printf("\n Error->3:Mismatched parentheses");
         case 4: printf("\n Error->4:Illegal character is expression");
         case 5: printf("\n Error->5:Multicharacter variable");
        }
     printf("\n Position of the cursor: %d", ifp);
     }

/* Definition of the function main */

    void main()
       {
         int err, ans;
         char infix[size],suffix[size];
         err = 0;
         input(infix);
         polish_fun(infix,suffix, &err);
         if(!err)
           {
         printf("\n The suffix form of the given, expression is: ");
         puts(suffix);
           }
       }

Posted in: Programming in C