#include <stdlib.h>#include <stdio.h>#include <string.h> #define MODE_POSTFIX     0#define MODE_ASSEMBLY    1 char    lookahead;int     pos;int     compile_mode;char    expression[20+1]; void error(){        printf("Syntax error!\n");} void match( char t ){        if( lookahead == t )        {                pos++;                lookahead = expression[pos];        }        else                error();} void digit(){        switch( lookahead )        {                case '0':                case '1':                case '2':                case '3':                case '4':                case '5':                case '6':                case '7':                case '8':                case '9':                        if( compile_mode == MODE_POSTFIX )                                printf("%c", lookahead);                        else                                printf("\tPUSH %c\n", lookahead);                         match( lookahead );                        break;                default:                        error();                        break;        }} void term(){        digit();        while(1)        {                switch( lookahead )                {                        case '*':                                match('*');                                digit();                                 printf( "%s", compile_mode == MODE_POSTFIX ? "*"                                        : "\tPOP B\n\tPOP A\n\tMUL A, B\n\tPUSH A\n");                                 break;                        case '/':                                match('/');                                digit();                                 printf( "%s", compile_mode == MODE_POSTFIX ? "/"                                        : "\tPOP B\n\tPOP A\n\tDIV A, B\n\tPUSH A\n");                                break;                        default:                                return;                }        }} void expr(){        term();        while(1)        {                switch( lookahead )                {                        case '+':                                match('+');                                term();                                 printf( "%s", compile_mode == MODE_POSTFIX ? "+"                                        : "\tPOP B\n\tPOP A\n\tADD A, B\n\tPUSH A\n");                                break;                        case '-':                                match('-');                                term();                                 printf( "%s", compile_mode == MODE_POSTFIX ? "-"                                        : "\tPOP B\n\tPOP A\n\tSUB A, B\n\tPUSH A\n");                                break;                        default:                                return;                }        }} int main ( int argc, char** argv ){        printf("Please enter an infix-notated expression with single digits:\n\n\t");        scanf("%20s", expression);         printf("\nCompiling to postfix-notated expression:\n\n\t");        compile_mode = MODE_POSTFIX;        pos = 0;        lookahead = *expression;        expr();         printf("\n\nCompiling to assembly-notated machine code:\n\n");        compile_mode = MODE_ASSEMBLY;        pos = 0;        lookahead = *expression;        expr();         return 0;}