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

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

Code for Program to convert an expression in postfix form to an infix form in C Programming

#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++ ;
    }
}