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convert postfix expression into prefix expression
Posted Date: 27 May 2008 Resource Type: Articles/Knowledge Sharing Category: Computer & Technology
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Posted By: Vidya Member Level: Diamond
Rating:  Points: 1
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Program : Program to convert postfix expression into prefix expression.
#include
#include
#include
#define SIZE 30
typedef struct fix_tag
{
char s[SIZE][SIZE], dest[SIZE] ;
char t1[2], t2[2] ;
char ch1[SIZE], ch2[SIZE], ch3[SIZE] ;
int i, top ;
}postfix ;
/********** Function Declaration begins **********/
void initialization ( postfix * ) ;
void expression ( postfix *, char * ) ;
void push ( postfix *, char * ) ;
void pop ( postfix *, char * ) ;
void trans ( postfix * ) ;
void display ( postfix ) ;
/********** Function Declaration ends **********/
void main( )
{
postfix PF ;
char exp[SIZE] ;
clrscr( ) ;
initialization( &PF ) ;
printf (“\n\t\t Enter any postfix expression:” ) ;
gets ( exp ) ;
expression ( &PF, exp ) ;
trans ( &PF ) ;
printf ( “\n\t\tThe resultant Prefix expression is: “ ) ;
display ( PF ) ;
getch( ) ;
}
/********** Initialization of Structure variable **********/
/********** Function Definition begins **********/
void initialization ( postfix *p )
{
p -> i = 0 ;
p -> top = -1 ;
strcpy ( p -> dest, “” ) ;
}
/********** Function Definition ends **********/
/********** String Copy **********/
/********** Function Definition begins **********/
void expression ( postfix *p, char *c )
{
strcpy ( p -> dest, c ) ;
}
/********** Function Definition ends **********/
/********** Pushing expression **********/
/********** Function Definition begins **********/
void push ( postfix *p, char *str )
{
if ( p -> top == SIZE - 1 )
printf ( “\nStack Overflow” ) ;
else
{
p -> top++ ;
strcpy ( p -> s[p -> top], str ) ;
}
}
/********** Function Definition ends **********/
/********** Popping expression **********/
/********** Function Definition begins **********/
void pop ( postfix *p, char *a )
{
if ( p -> top == -1 )
printf ( “\nStack is empty.” ) ;
else
{
strcpy ( a, p -> s[p -> top] ) ;
p -> top— ;
}
}
/********** Function Definition ends **********/
/********** Postfix to Prefix **********/
/********** Function Definition begins **********/
void trans ( postfix *p )
{
while ( p -> dest[p -> i] != ‘\0’ )
{
if ( p -> dest[p -> i] == ‘ ‘)
p -> i++ ;
if( p -> dest[p -> i] == ‘%’ || p -> dest[p -> i] == ‘*’ ||
p -> dest[p -> i] == ‘-’ || p -> dest[p -> i] == ‘+’ ||
p -> dest[p -> i] == ‘/’ || p -> dest[p -> i] == ‘$’ )
{
pop ( p, p -> ch2 ) ;
pop ( p, p -> ch3 ) ;
p -> t1[0] = p -> dest[ p -> i] ;
p -> t1[1] = ‘\0’ ;
strcpy ( p -> ch1, p -> t1 ) ;
strcat ( p -> ch1, p -> ch3 ) ;
strcat ( p -> ch1, p -> ch2 ) ;
push ( p, p -> ch1 ) ;
}
else
{
p -> t1[0] = p -> dest[p -> i] ;
p -> t1[1] = ‘\0’ ;
strcpy ( p -> t2, p -> t1 ) ;
push ( p, p -> t2 ) ;
}
p -> i++ ;
}
}
/********** Function Definition ends **********/
/********** Displaying expression **********/
/********** Function Definition begins **********/
void display ( postfix p )
{
char *t = p.s[0] ;
while ( *t )
{
printf ( “%c “, *t ) ;
t++ ;
}
}
/********** Function Definition ends **********/
? OUTPUT
Enter any postfix expression:AB+C/D-
The resultant Prefix expression is: - / + A B C D
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