스택을 이용한 계산기 프로그램

#include <stdio.h>
#include <stdlib.h>
 
#define MAX_STACK_SIZE 100 
#define MAX_EXPR_SIZE 100 
 
char expr[MAX_EXPR_SIZE] = "(((8/2)-3)+(4*2))";
 
typedef enum {rparen, lparen, plus, minus, times, divide, eos, operand} input_char ;
 
static input_char stack[MAX_STACK_SIZE];
 
int action[7][7] ={      /*?? ) ? (? +  -  *? /? eos */ 
   	          	 /*? ) */ {-1, 2, 1, 1, 1, 1, -1}, 
			 /*? ( */ {-1, 0, 0, 0, 0, 0, 0}, 
              /* input */ /* + */ {-1, 0, 1, 1, 1, 1, 0}, 
			 /* -? */ {-1, 0, 1, 1, 1, 1, 0}, 
		        /* *? */  {-1, 0, 0, 0, 1, 1, 0}, 
		        /* /? */  {-1, 0, 0, 0, 1, 1, 0}, 
			/* eos */ {-1,-1, 1, 1, 1, 1, 3} }; 
 
static	int top = -1; 
 
// - 후위 표기식 변환 함수 
void push( int *, input_char );
input_char pop( int *);
void postfix( void );
input_char get_token(char *, int *	);
int stack_top( int );
void print_token( input_char );
int eval( void );
input_char get_next_token( char *, int * );
 
int main( void ){
	int top = -1;
	printf("fostfix: %s\n\n", expr);
 
	postfix();
 
	printf("\n\nresult: %d", eval());
 
	system( "pause" );
	return 0;
}
 
void postfix(void)  { 
	int n = 0; 	/* 입력 문자열의 위치 */ 
	char symbol;
 	int done;
 
	input_char token;
 
	push(&top, eos); /* 스택의 초기 상태 */ 
	token = get_token(&symbol, &n); 
	done = 0; /* false */ 
 
	while (!done) { 
		if (token == operand) { 
			printf("%c ", symbol); 
			token = get_token(&symbol, &n); 
		} 
		else { 
			switch (action[token][stack_top(top)]) { 
				case -1: /* 오류 */ 
					break; 
				case 0:  push(&top, token);   // push 
					token = get_token(&symbol, &n); 
					break; 
				case 1:	/* pop, print, .... */ 
					print_token(pop(&top));
					break; 
				case 2: /* pop */ 
					pop(&top); /* delete lparen */ 
					token = get_token(&symbol, &n); 
					break; 
				case 3: /* done */ done = 1; /* true */ 
			} /* end of switch */ 
		} 
	} /* end of while */ 
} 
 
void push( int *in, input_char data )  { 
	if (*in >= MAX_STACK_SIZE - 1) {	 /* 스택 포화 상태 */ 
		fprintf(stderr, "Stack full"); 
		exit(1); 
	} 
 
	stack[++*in] = data; 
} 
 
input_char pop(int *out)  { 
	if (*out < 0) { 
		fprintf(stderr, "Stack Empty\n" ); 
		return eos;	// 스택에 존재하지 않는 코드를 반환 
	}
 
	//printf("[pop= %d]\n ", stack[*out]);
	return stack[(*out)--]; 
} 
 
input_char get_token(char *symbol, int *n)  { 
	*symbol = expr[(*n)++]; 
 
	switch (*symbol) { 
		case '(' : return lparen; 
		case ')' : return rparen; 
		case '+' : return plus; 
		case '-' : return minus; 
		case '/' : return divide; 
		case '*' : return times; 
		case '\0': return eos; 
		default  : return operand; 
	} 
}  
 
int stack_top( int top)
{
	if (top < 0 ) {
		fprintf(stderr, "Stack Empty");
		return -1;
	}
 
	return stack[top];
}
 
void print_token( input_char in )
{
	switch ( in ) { 
		case lparen : printf("%c ", '(' );  
			break;
		case rparen : printf("%c ", ')' ); 
			break;
		case plus   : printf("%c ", '+' ); 
			break;
		case minus  : printf("%c ", '-'); 
			break;
		case divide : printf("%c ", '/'); 
			break;
		case times  : printf("%c ", '*'); 
			break;
	} 
}
 
int eval( void )
{
	input_char token;
	char symbol;
	int op1, op2;
	int n=0;
 
	token = get_next_token( &symbol, &n );
 
	while ( token != eos ) {
		if ( token == operand ) push( &top, (input_char)atoi( &symbol ) );
		else {
			op2 = pop( &top );
			op1 = pop( &top );
 
			switch ( token ) {
				case plus   : push( &top, (input_char)(op1 + op2)) ;
					break;	
				case minus  : push( &top, (input_char)(op1 - op2) );
					break;		
				case times  : push( &top, (input_char)(op1 * op2) );
					break;
				case divide : push( &top, (input_char)(op1 / op2) );
					break;
			}
		}
		token = get_next_token( &symbol, &n );
	}
	return pop( &top );
}
 
input_char get_next_token( char *symbol, int *n )
{
	*symbol = expr[ (*n)++ ];
 
	switch ( *symbol ) {
		case '+'  : return plus;
		case '-'  : return minus;
		case '/'  : return divide;
		case '*'  : return times;
		case '\0' : return eos;
		default   : return operand;
	}
}