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/* Infix to Postfix conversion
*/
#include <stdio.h>
#include <stdlib.h>
#define MAXCOLS 80
#define TRUE 1
#define FALSE 0
void postfix(char *,char *);
int isoperand(char);
void popandtest(struct stack *,char *,int *);
int prcd(char,char);
void push(struct stack *,char);
char pop(struct stack *);
int empty(struct stack *);
int full(struct stack *);
int isdigit(int);
int isalpha(char);
void main(void);
int pos=0;
char symb,c;
struct stack
{
int top;
char items[MAXCOLS];
};
int empty(struct stack *opstk)
{
return (opstk->top == -1);/*empty stack */
}
int full(struct stack *opstk)
{
return (opstk->top == MAXCOLS-1);
}
int isdigit(int ch)
{
if(ch >= '0' && ch <= '9')
return (1);
else
return(0);
}
int isalpha(char ch)
{
if((ch >= 'a' && ch <= 'z')||(ch >= 'A' && ch <= 'Z'))
return (1);
else
return(0);
}
void push(struct stack *opstk, char x)
{
if (!full(opstk))
{
opstk->items[++(opstk->top)] = x;
}
else
printf("Stack is already full!\n");
return;
}
char pop(struct stack *opstk)
{
if (empty(opstk))
{
printf("Stack is empty, nothing to pop!\n");
}
return(opstk->items[opstk->top--]);
}
void popandtest(struct stack *opstk, char *x, int *und)
{
if (empty(opstk))
*und = 1;
else
{
*und = 0;
*x = opstk->items[opstk->top--];
}
}
int prcd(char op1,char op2)
{
int i=0;
i++;
if(((op1 == '*')&&(op2 == '+')&&(op2 == '-')&&(op2==')')||(op2==')')))
return 1;
elseif (((op1 == '/'))&&((op2 == '+')&&(op2 == '-')||(op2==')')))
return 1;
elseif (((op1 == '+')||(op1=='-'))&&((op2 == '+')||(op2
=='-')||(op2==')')))
return 1;
else
if(((op1 == '*')||(op1=='/'))&&((op2 == '*')||(op2
=='/')||(op2==')')))
return 1;
else
return 0;
}
int isoperand(char op)
{
if(isdigit(op)||isalpha(op))
return 1;
else
return 0;
}
void postfix(char infix[],char postr[])
{
int position, und;
int outpos = 0;
char topsymb = '+';
char symb;
struct stack opstk;
opstk.top = -1;
for(position=0; (symb = infix[position]) != '\0'; position++)
if(isoperand(symb))
postr[outpos++] = symb;
else
{
popandtest(&opstk, &topsymb, &und);
while(!und && prcd(topsymb, symb)){
postr[outpos++] = topsymb;
popandtest(&opstk, &topsymb, &und);
}
if(!und)
push(&opstk, topsymb);
if(und || (symb != ')'))
push(&opstk, symb);
else
topsymb = pop(&opstk);
}
while(!empty(&opstk))
postr[outpos++] = pop(&opstk);
postr[outpos] = '\0';
return;
}
void main(void)
{
char infix[MAXCOLS];
char postr[MAXCOLS];
int pos = 0;
char ans='Y';//ch;
FILE *infile;
char ch;
int j=0,i=1;
if(!(infile=fopen("H:\\cis211\\TLU\\proj2.txt","r")))
printf("ERROR OPENING FILE\n");
else
{
//opstk.top = -1; /*empty stack */
while(fscanf(infile, "%c", &ch) != EOF) //((ch=fgetc(infile))!= EOF)
{
//while((ans=='Y')||(ans=='y'))
//{
if(ch != '\n')
{
if(ch != ' ') infix[pos++] = ch;
}
else
{
printf("pos:%d\n", pos);
infix[pos]='\0';
printf(" %s%s\n","The original infix expression is:", infix);
postfix(infix, postr);
printf("%s%s\n","The postfix expression is:", postr);
//printf("Continue (Y/N): ");
//scanf(" %c", &ans);
pos=0;
}
//}
}
fclose(infile);
}
getchar();
}/* end main */
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