Program to convert an expression in postfix form to an infix form

/* Program to convert an expression in postfix form to an infix form */

#include <stdio.h>
#include <conio.h>
#include <string.h>

#define MAX 50

struct postfix
{
char stack[MAX][MAX], target[MAX] ;
char temp1[2], temp2[2] ;
char str1[MAX], str2[MAX], str3[MAX] ;
int i, top ;
} ;

void initpostfix ( struct postfix * ) ;
void setexpr ( struct postfix *, char * ) ;
void push ( struct postfix *, char * ) ;
void pop ( struct postfix *, char * ) ;
void convert ( struct postfix * ) ;
void show ( struct postfix ) ;

void main( )
{
struct postfix q ;
char expr[MAX] ;

clrscr( ) ;

initpostfix ( &q ) ;

printf ( "\nEnter an expression in postfix form: " ) ;
gets ( expr ) ;

setexpr ( &q, expr ) ;
convert ( &q ) ;

printf ( "\nThe infix expression is: " ) ;
show ( q ) ;

getch( ) ;
}

/* initializes data member */
void initpostfix ( struct postfix *p )
{
p -> i = 0 ;
p -> top = -1 ;
strcpy ( p -> target, "" ) ;
}

/* copies given expression to target string */
void setexpr ( struct postfix *p, char *c )
{
strcpy ( p -> target, c ) ;
}

/* adds an expr. to the stack */
void push ( struct postfix *p, char *str )
{
if ( p -> top == MAX - 1 )
printf ( "\nStack is full." ) ;
else
{
p -> top++ ;
strcpy ( p -> stack[p -> top], str ) ;
}
}

/* pops an expr. from the stack */
void pop ( struct postfix *p, char *a )
{
if ( p -> top == -1 )
printf ( "\nStack is empty." ) ;
else
{
strcpy ( a, p -> stack[p -> top] ) ;
p -> top-- ;
}
}

/* converts given expr. to infix form */
void convert ( struct postfix *p )
{
while ( p -> target[p -> i] )
{
/* skip whitespace, if any */
if( p -> target[p -> i] == ' ' )
p -> i++ ;
if ( p -> target[p -> i] == '%' || p -> target[p -> i] == '*' ||
p -> target[p -> i] == '-' || p -> target[p -> i] == '+' ||
p -> target[p -> i] == '/' || p -> target[p -> i] == '$' )
{
pop ( p, p -> str2 ) ;
pop ( p, p -> str3 ) ;
p -> temp1[0] = p -> target[p -> i] ;
p -> temp1[1] = '\0' ;
strcpy ( p -> str1, p -> str3 ) ;
strcat ( p -> str1, p -> temp1 ) ;
strcat ( p -> str1, p -> str2 ) ;
push ( p, p -> str1 ) ;
}
else
{
p -> temp1[0] = p -> target[p -> i] ;
p -> temp1[1] = '\0' ;
strcpy ( p -> temp2, p -> temp1 ) ;
push ( p, p -> temp2 ) ;
}
p -> i++ ;
}
}

/* displays the expression */
void show ( struct postfix p )
{
char *t ;
t = p.stack[0] ;
while ( *t )
{
printf ( "%c ", *t ) ;
t++ ;
}
}