m.c

/* # run this example using the program below
n = 1;
f = 1;

while (n <= 7) {
    f = f * n;
    print f;
    n = n + 1;
}

if (f == 5040) print 1; else print 0; */

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

static char src [ 65536                                                      ] , * p = src ; static
int t , n , a [ 26 ] ;                                                       static void die ( void
) { fputs ( "error\n" ,                                                      stderr ) ; exit ( 1 ) ;
} static void next (                                                         void ) { char * q ; int
k ; while ( * p && * p                                                       <= 32 ) ++ p ; if ( * p
== '#' ) { while ( * p                                                       && * p != '\n' ) ++ p ;
next ( ) ; return ; } t                                                      = ( unsigned char ) * p
; if ( ! t ) return ;                                                        ++ p ; if ( t >= '0' &&
t <= '9' ) { n = ( int )                                                    strtol ( p - 1 , & p ,
10 ) ; t = 'V' ; } else                                                    if ( t >= 'a' && t <= 'z'
) { q = p - 1 ; while ( *                                                 p >= 'a' && * p <= 'z' )
++ p ; k = ( int ) ( p - q                                               ) ; if ( k == 1 ) { n = * q
- 'a' ; t = 'A' ; } else if                                             ( k == 2 && ! memcmp ( q ,
"if" , 2 ) ) t = 'I' ; else                                            if ( k == 4 && ! memcmp ( q ,
"else" , 4 ) ) t = 'E' ; else                                         if ( k == 5 && ! memcmp ( q ,
"while" , 5 ) ) t = 'W' ; else                                       if ( k == 5 && ! memcmp ( q ,
"print" , 5 ) ) t = 'P' ; else                                      die ( ) ; } else if ( * p == '='
&& ( t == '=' || t == '!' || t ==                                  '<' || t == '>' ) ) { ++ p ; t =
t == '=' ? 'Q' : t == '!' ? 'N' :                                 t == '<' ? 'L' : 'G' ; } else if (
( t == '&' || t == '|' ) && * p ==                               t ) ++ p ; else if ( t == '&' || t
== '|' || ! strchr (                                            "+-*/%<>=!(){};" , t ) ) die ( ) ; }
static void need ( int c ) { if ( t                            != c ) die ( ) ; next ( ) ; } static
int prec ( void ) { if ( ! t ) return                         0 ; return t == '|' ? 1 : t == '&' ? 2
: strchr ( "QN" , t ) ? 3 : strchr (                         "<>LG" , t ) ? 4 : strchr ( "+-" , t )
? 5 : strchr ( "*/%" ,  t ) ? 6 : 0 ; }                     static int expr  ( int m , int run ) {
int x , y , o , k ; if   ( t == '+' || t                   == '-' || t ==    '!' ) { o = t ; next (
) ; x = expr ( 7 , run    ) ; if ( run ) x                = o == '-' ? - x   : o == '!' ? ! x : x ;
} else if ( t == '(' )     { next ( ) ; x =              expr ( 1 , run )    ; need ( ')' ) ; } else
if ( t == 'V' || t ==       'A' ) { x = t ==            'V' ? n : a [ n      ] ; next ( ) ; } else {
die ( ) ; return 0 ; }       while ( ( k =             prec ( ) ) >= m       ) { o = t ; next ( ) ;
y = expr ( k + 1 , run        && ! ( o == '&'         && ! x ) && ! (        o == '|' && x ) ) ; if
( run ) { if ( ( o ==         '/' || o == '%'         ) && ! y ) die (       ) ; x = o == '+' ? x +
y : o == '-' ? x - y :         o == '*' ? x * y      : o == '/' ? x /        y : o == '%' ? x % y :
o == '<' ? x < y : o ==         '>' ? x > y : o     == 'L' ? x <= y          : o == 'G' ? x >= y : o
== 'Q' ? x == y : o ==           'N' ? x != y : o  == '&' ? x && y           : x || y ; } } return x
; } static void stmt (            int run ) { int c , v ; char * q           ; if ( t == '{' ) {
next ( ) ; while ( t &&            t != '}' ) stmt ( run ) ; need            ( '}' ) ; } else if ( t
== 'I' ) { next ( ) ;                                                        need ( '(' ) ; c = expr
( 1 , run ) ; need (                                                         ')' ) ; stmt ( run && c
) ; if ( t == 'E' ) {                                                        next ( ) ; stmt ( run
&& ! c ) ; } } else if                                                       ( t == 'W' ) { q = p ;
do { p = q ; next ( ) ;                                                      need ( '(' ) ; c = expr
( 1 , run ) ; need (                                                         ')' ) ; stmt ( run && c
) ; } while ( run && c                                                       ) ; } else if ( t ==
'P' ) { next ( ) ; v =                                                       expr ( 1 , run ) ; need
( ';' ) ; if ( run )                                                         printf ( "%d\n" , v ) ;
} else if ( t == 'A' )                                                       { c = n ; next ( ) ;
need ( '=' ) ; v = expr                                                      ( 1 , run ) ; need (
';' ) ; if ( run ) a [                                                       c ] = v ; } else need (
';' ) ; } int main (                                                         int argc , char * *
argv ) { FILE * f =                                                          stdin ; size_t len ; if
( argc > 2 ) die ( ) ;                                                       if ( argc == 2 ) { f =
fopen ( argv [ 1 ] ,                                                         "rb" ) ; if ( ! f ) die
( ) ; } len = fread (                                                        src , 1 , sizeof ( src
) - 1 , f ) ; if (                                                           ferror ( f ) || fgetc (
f ) != EOF || memchr (                                                       src , 0 , len ) ) die (
) ; if ( f != stdin )                                                        fclose ( f ) ; next ( )
; while ( t ) stmt ( 1                                                       ) ; return 0 ; }