Expression storage

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#include <stdio.h>

#include <ctype.h>

#include <string.h>

#define OPERAND 255

#define OPERATOR -255

enum Priority  

{

    SUB_OP,

    ADD_OP,

    DIV_OP,

    MUL_OP,

    LAST_OP

};

struct Symbol

{

   char *symbol;

   char type;

   char *value;

};

struct Symbol symtbl[256];

int max_sym=0;

void Symbol_insert(char *sym,char typ,char *val)

{

    symtbl[max_sym].symbol = sym;

    symtbl[max_sym].type = typ;

    symtbl[max_sym].value = val;

    max_sym++;

}

int Symbol_search(char *sym)

{

    for(int i=0; i<max_sym; i++)

    {

        if(strcmp(sym,symtbl[max_sym].symbol)==0)

        {

            return i;

        }

    }

   return -1; 

}

struct ListNode

{

    int isOperatorOrOperand;

    int priority;

    struct Symbol *str;

    char op;

};

struct ListNode prQue[1024]; // Priority Queue

int size =0;

int maximum()

{

}

void fill(int isType,int pr, struct Symbol *s, char op )

{

  prQue[size].isOperatorOrOperand = isType;

  prQue[size].priority = pr;

  if(isType ==  OPERAND)

  {

    prQue[size].str = s;

    prQue[size].isOperatorOrOperand = OPERAND;

  }

  else

  {  prQue[size].op = op;

     prQue[size].isOperatorOrOperand = OPERATOR;

  }

  size++;

}

int insert(char *str)

{

    static int blocklevel = LAST_OP - 1;

   static int priority =1;

   char *s;

   char string_c[100];

   if(*str == '*')

   {

       priority = MUL_OP;

       fill(OPERATOR,priority + blocklevel,NULL, MUL_OP );

       return 1;

   }

   else if(*str == '/')

   {

       priority = DIV_OP;

       fill(OPERATOR,priority + blocklevel,NULL, DIV_OP );

       return 1;

   }

   else if(*str == '+')

   {

       priority = ADD_OP;

       fill(OPERATOR,priority + blocklevel,NULL, ADD_OP );

       return 1;

   }

   else if(*str == '-')

   {

       priority = SUB_OP;

       fill(OPERATOR,priority + blocklevel,NULL, SUB_OP );

       return 1;

   }

   else if(*str == '(')

   {

       blocklevel++;

       return 1;

   }

   else if(*str == ')')

   {

       blocklevel--;

       return 1;

   }

   else if(isalpha(*str))

   {   int i=0,index;

       s = str;

       while(isalpha(*str) || isdigit(*str))

       {  str++;

           i++;

       }

       strncpy(string_c,s,i);

       string_c[i]='\0';

       index=Symbol_search(string_c);

       if(index != -1)

       {

           fill(OPERAND,priority + blocklevel,&symtbl[max_sym] ,'\0');

       }

       else

       {

          printf("Symbol %s not found !",string_c );

       }

       

       return i;

   }

        

}

int main()

{

    char arr[100] = "a+b-c*d";

    for(int i=0; i< strlen(arr); )

    {

        i+= insert(arr+i);

    }

    return 0;

}