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Program to convert an Infix form to Postfix form

Posted By: Julia Hughes     Category: C Programming     Views: 29482

Program to convert an Infix form to Postfix form.

Code for Program to convert an Infix form to Postfix form in C Programming

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

#define MAX 50

struct infix
{
    char target[MAX] ;
    char stack[MAX] ;
    char *s, *t ;
    int top ;
} ;

void initinfix ( struct infix * ) ;
void setexpr ( struct infix *, char * ) ;
void push ( struct infix *, char ) ;
char pop ( struct infix * ) ;
void convert ( struct infix * ) ;
int priority ( char ) ;
void show ( struct infix ) ;

void main( )
{
    struct infix p ;
    char expr[MAX] ;

    initinfix ( &p ) ;

    clrscr( ) ;

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

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

    printf ( "\nThe postfix expression is: " ) ;
    show ( p ) ;

    getch( ) ;
}

/* initializes structure elements */
void initinfix ( struct infix *p ) { p -> top = -1 ; strcpy ( p -> target, "" ) ; strcpy ( p -> stack, "" ) ; p -> t = p -> target ; p -> s = "" ; } /* sets s to point to given expr. */
void setexpr ( struct infix *p, char *str ) { p -> s = str ; } /* adds an operator to the stack */
void push ( struct infix *p, char c ) { if ( p -> top == MAX ) printf ( "\nStack is full.\n" ) ; else { p -> top++ ; p -> stack[p -> top] = c ; } } /* pops an operator from the stack */
char pop ( struct infix *p ) { if ( p -> top == -1 ) { printf ( "\nStack is empty.\n" ) ; return -1 ; } else { char item = p -> stack[p -> top] ; p -> top-- ; return item ; } } /* converts the given expr. from infix to postfix form */
void convert ( struct infix *p ) { char opr ; while ( *( p -> s ) ) { if ( *( p -> s ) == ' ' || *( p -> s ) == '\t' ) { p -> s++ ; continue ; } if ( isdigit ( *( p -> s ) ) || isalpha ( *( p -> s ) ) ) { while ( isdigit ( *( p -> s ) ) || isalpha ( *( p -> s ) ) ) { *( p -> t ) = *( p -> s ) ; p -> s++ ; p -> t++ ; } } if ( *( p -> s ) == '(' ) { push ( p, *( p -> s ) ) ; p -> s++ ; } if ( *( p -> s ) == '*' || *( p -> s ) == '+' || *( p -> s ) == '/' || *( p -> s ) == '%' || *( p -> s ) == '-' || *( p -> s ) == '$' ) { if ( p -> top != -1 ) { opr = pop ( p ) ; while ( priority ( opr ) >= priority ( *( p -> s ) ) ) { *( p -> t ) = opr ; p -> t++ ; opr = pop ( p ) ; } push ( p, opr ) ; push ( p, *( p -> s ) ) ; } else push ( p, *( p -> s ) ) ; p -> s++ ; } if ( *( p -> s ) == ')' ) { opr = pop ( p ) ; while ( ( opr ) != '(' ) { *( p -> t ) = opr ; p -> t++ ; opr = pop ( p ) ; } p -> s++ ; } } while ( p -> top != -1 ) { char opr = pop ( p ) ; *( p -> t ) = opr ; p -> t++ ; } *( p -> t ) = '\0' ; } /* returns the priority of an operator */
int priority ( char c ) { if ( c == '$' ) return 3 ; if ( c == '*' || c == '/' || c == '%' ) return 2 ; else { if ( c == '+' || c == '-' ) return 1 ; elsereturn 0 ; } } /* displays the postfix form of given expr. */
void show ( struct infix p ) { printf ( " %s", p.target ) ; }
  
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Julia Hughes
Julia Hughes author of Program to convert an Infix form to Postfix form is from London, United Kingdom.
 
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