/* 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);
}
}
