calc.cpp

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

typedef enum
{
	TOK_NUM,
	TOK_PLUS,
	TOK_MINUS,
	TOK_MUL,
	TOK_INVALID,
}TOK_TYPE;

#define BUF_SIZE (16)

TOK_TYPE get_num(FILE *_fp, int *_num)
{
	int c;
	char buf[BUF_SIZE];
	int i = 0;

	while ((c = fgetc(_fp)) != '\n' && c != EOF)
	{
		buf[i++] = c;

		if (!isdigit(c))
		{
			return TOK_INVALID;
		}
	}
	buf[i] = '\0';

	*_num = strtol(buf, NULL, 10);

	return TOK_NUM;
}

TOK_TYPE get_tok(FILE *_fp)
{
	int c;
	c = fgetc(_fp);

	if (c == '+')
	{
		//printf("+\n");
		return TOK_PLUS;
	}
	else if (c == '-')
	{
		//printf("-\n");
		return TOK_MINUS;
	}
	else if (c == '*')
	{
		//printf("*\n");
		return TOK_MUL;
	}

	return TOK_INVALID;
}

void main()
{
	printf("input first num  : ");
	int a;
	if (get_num(stdin, &a) == TOK_INVALID)
	{
		printf("invalid num\n");
		return;
	}


	printf("input operator   : ");
	TOK_TYPE op;
	op = get_tok(stdin);

	if (op == TOK_INVALID)
	{
		printf("invalid operator\n");
		return;
	}
	getchar();


	printf("input second num : ");
	int b;
	if (get_num(stdin, &b) == TOK_INVALID)
	{
		printf("invalid num\n");
		return;
	}


	if (op == TOK_PLUS)
	{
		printf("first + second   = %d\n", a + b);
	}
	else if (op == TOK_MINUS)
	{
		printf("first - second   = %d\n", a - b);
	}
	else if (op == TOK_MUL)
	{
		printf("first * second   = %d\n", a * b);
	}
}