Good day DaniWeb experts.
This is my first post here and hope you can help me with my problem. I'm a noob with Borand C++.
I see a tutorial here "Converting and Evaluating Infix, Postfix and Prefix Expressions in C". I copied the code and run it in my Borland C++ program.
Problem with "Infix to Postfix"
Here's what I get if I run the code:
[img]http://i168.photobucket.com/albums/u162/SHENGTON/AnabelInfixtoPostfix.jpg[/img]
I'll just include the code here:
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define MAX 10
#define EMPTY -1
struct stack
{
char data[MAX];
int top;
};
int isempty(struct stack *s)
{
return (s->top == EMPTY) ? 1 : 0;
}
void emptystack(struct stack* s)
{
s->top=EMPTY;
}
void push(struct stack* s,int item)
{
if(s->top == (MAX-1))
{
printf("\nSTACK FULL");
}
else
{
++s->top;
s->data[s->top]=item;
}
}
char pop(struct stack* s)
{
char ret=(char)EMPTY;
if(!isempty(s))
{
ret= s->data[s->top];
--s->top;
}
return ret;
}
void display(struct stack s)
{
while(s.top != EMPTY)
{
printf("\n%d",s.data[s.top]);
s.top--;
}
}
int isoperator(char e)
{
if(e == '+' || e == '-' || e == '*' || e == '/' || e == '%')
return 1;
else
return 0;
}
int priority(char e)
{
int pri = 0;
if(e == '*' || e == '/' || e =='%')
pri = 2;
else
{
if(e == '+' || e == '-')
pri = 1;
}
return pri;
}
void infix2postfix(char* infix, char * postfix, int insertspace)
{
char *i,*p;
struct stack X;
char n1;
emptystack(&X);
i = &infix[0];
p = &postfix[0];
while(*i)
{
while(*i == ' ' || *i == '\t')
{
i++;
}
if( isdigit(*i) || isalpha(*i) )
{
while( isdigit(*i) || isalpha(*i))
{
*p = *i;
p++;
i++;
}
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
}
if( *i == '(' )
{
push(&X,*i);
i++;
}
if( *i == ')')
{
n1 = pop(&X);
while( n1 != '(' )
{
*p = n1;
p++;
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
n1 = pop(&X);
}
i++;
}
if( isoperator(*i) )
{
if(isempty(&X))
push(&X,*i);
else
{
n1 = pop(&X);
while(priority(n1) >= priority(*i))
{
*p = n1;
p++;
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
n1 = pop(&X);
}
push(&X,n1);
push(&X,*i);
}
i++;
}
}
while(!isempty(&X))
{
n1 = pop(&X);
*p = n1;
p++;
/*SPACE CODE*/
if(insertspace)
{
*p = ' ';
p++;
}
/*END SPACE CODE*/
}
*p = '\0';
}
int main()
{
char in[50],post[50];
strcpy(&post[0],"");
printf("Enter Infix Expression : ");
fflush(stdin);
gets(in);
infix2postfix(&in[0],&post[0],1);
printf("Postfix Expression is : %s\n",&post[0]);
return 0;
}
/* SAMPLE OUTPUT:
Enter Infix Expression : A + B + C / (E - F)
Postfix Expression is : A B + C E F - / +
*/Problem with "Postfix to Infix"
Here's the code of Postfix to Infix conversion:
/* include necessary preprocessor header files */
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
/* constants */
#define TRUE 1
#define FALSE 0
/* structure for stack */
typedef struct
{
char data[20]; /* array to hold stack contents */
int tos; /* top of the stack pointer */
} STACK;
/* function prototypes */
void initStack(STACK *stack);
void get_postfix(char infix[]);
void convertToinfix(char postfix[], char infix[]);
int isOperator(char c);
int precedence(char operator1, char operator2);
int pred_level(char ch);
void push(STACK *stack, char value);
char pop(STACK *stack);
char stackTop(STACK *stack);
int isEmpty(STACK *stack);
int isFull(STACK *stack);
void printResult(char postfix[], char infix[]);
void print_msg(void);
int main(void)
{
char postfix[20], infix[20] ="";
//float result;
/* convert from infix to postfix main function */
convertToinfix(postfix, infix);
/* display the infix equivalent */
infix[strlen(postfix)-2] = '\0';
printResult(postfix, infix /*, result*/);
return EXIT_SUCCESS;
}
void initStack(STACK *stack)
{
stack->tos = -1; /* stack is initially empty */
}
void get_postfix(char postfix[])
{
int i;
printf("Enter postfix expression below (max 18 characters excluding spaces) : \n");
fflush(stdin);
/* to read in only 18 characters excluding spaces */
for ( i=0; i<18; )
{
if ( (postfix[i] = getchar()) == '\n' )
{
i++;
break;
}
else if ( !(isspace(postfix[i])) )
i++;
}
postfix[i] = '\0';
}
void convertToinfix(char postfix[], char infix[])
{
int i, length;
int j=0;
char tos_ch;
STACK stack;
initStack(&stack); /* initialise stack */
get_postfix(postfix); /* get postfix expression from user */
length = strlen(postfix);
/* if strlen if postfix is more than zero */
if ( length )
{
push(&stack, '(');
strcat(postfix, ")");
length++;
for ( i=0; i<length; i++ )
{
/* if current operator in postfix is digit */
if ( isdigit(postfix[i]) )
{
infix[j++] = postfix[i];
}
/* if current operator in postfix is left parenthesis */
else if ( postfix[i] == '(' )
{
push(&stack, '(');
}
/* if current operator in postfix is operator */
else if ( isOperator(postfix[i]) )
{
while ( TRUE )
{
/* get tos */
tos_ch = stackTop(&stack);
/* no stack left */
if ( tos_ch == '\0' )
{
printf("\nInvalid postfix expression\n");
print_msg();
exit(1);
}
else
{
if ( isOperator(tos_ch) )
{
if ( pred_level(tos_ch) >= pred_level(postfix[i]) )
infix[j++] = pop(&stack);
else
break;
}
else
break;
}
}
push(&stack, postfix[i]);
}
/* if current operator in postfix is right parenthesis */
else if ( postfix[i] == ')' )
{
while ( TRUE )
{
/* get tos */
tos_ch = stackTop(&stack);
/* no stack left */
if ( tos_ch == '\0' )
{
printf("\nInvalid postfix expression\n");
print_msg();
exit(1);
}
else
{
if ( tos_ch != '(' )
{
infix[j++] = tos_ch;
pop(&stack);
}
else
{
pop(&stack);
break;
}
}
}
continue;
}
}
}
infix[j] = '\0';
}
/* determine if c is an operator */
int isOperator(char c)
{
if ( c == '+' || c == '-' || c == '*' ||
c == '/' || c == '%' || c == '^' )
{
return TRUE;
}
else
return FALSE;
}
/* determine precedence level */
int pred_level(char ch)
{
if ( ch == '+' || ch == '-' )
return 1;
else if ( ch == '^' )
return 3;
else
return 2;
}
/* determine if the precedence of operator1 is less than,
equal to, greater than the precedence of operator2 */
int precedence(char operator1, char operator2)
{
if ( pred_level(operator1) > pred_level(operator2) )
return 1;
else if ( pred_level(operator1) < pred_level(operator2) )
return -1;
else
return 0;
}
/* push a value on the stack */
void push(STACK *stack, char value)
{
if ( !(isFull(stack)) )
{
(stack->tos)++;
stack->data[stack->tos] = value;
}
}
/* pop a value off the stack */
char pop(STACK *stack)
{
char ch;
if ( !(isEmpty(stack)) )
{
ch = stack->data[stack->tos];
(stack->tos)--;
return ch;
}
else
return '\0';
}
/* return the top value of the stack without popping the stack */
char stackTop(STACK *stack)
{
if ( !(isEmpty(stack)) )
return stack->data[stack->tos];
else
return '\0';
}
/* determine if stack is empty */
int isEmpty(STACK *stack)
{
/* empty */
if ( stack->tos == -1 )
return TRUE;
/* not empty */
else
return FALSE;
}
/* determine if stack is full */
int isFull(STACK *stack)
{
/* full */
if ( stack->tos == 19 )
return TRUE;
/* not full */
else
return FALSE;
}
/* display the result postfix expression */
void printResult(char postfix[], char infix[]/*, float result*/)
{
/*system("cls");*/
printf("\n\n");
printf("Postfix notation: %s\n\n", postfix);
printf("Infix notation : %s\n", infix);
//printf("Result is: %f\n", result);
print_msg();
}
/* print exit message */
void print_msg(void)
{
printf("Hit <RETURN> to exit......");
fflush(stdin);
getchar();
}When I run this code this what I get:
[img]http://i168.photobucket.com/albums/u162/SHENGTON/AningPostfixtoInfix1.jpg[/img]
When I press enter this is the result:
[img]http://i168.photobucket.com/albums/u162/SHENGTON/AningPostfixtoInfix2.jpg[/img]
What's wrong with the code?
I'm just a beginner with Borland C++. Hope you can help me with this Gurus.
Thanks and God bless. :)
