fsmnum.cpp

编译原理课程中通过有限状态机模型实现判定输入字符串是否为实数的源程序。

#include "stdio.h"
int isRealNumber(char *p)
{
	int state=1;
	int resualt=-1;
	while (*p)
	{
		switch(state)
		{
		case 1:
			if ('+'==*p||'-'==*p)
			{
				state=2;
			}
			else if (*p>='0'&&*p<='9')
			{
				state=4;
			}
			else if ('.'==*p)
			{
				state=3;
			}
			else
			{
				state=0;
			}
			break;
		case 2:
			if (*p>='0'&&*p<='9')
			{
				state=4;
			}
			else if ('.'==*p)
			{
				state=3;
			}
			else
			{
				state=0;
			}
			break;
		case 3:
			if (*p>='0'&&*p<='9')
			{
				state=5;
			}
			else
			{
				state=0;
			}
		    break;
		case 4:
			if (*p>='0'&&*p<='9')
			{
				state=4;
			}
			else if ('.'==*p)
			{
				state=5;
			}
			else
			{
				state=0;
			}
		    break;
		case 5:
			if (*p>='0'&&*p<='9')
			{
				state=5;
			}
			else
			{
				state=0;
			}
		    break;
		}
		if ('0'==state)
		{
			return -1;
		}
		p++;
	}
	if (4==state||5==state)
	{
		resualt=0;
	}
	return resualt;
}
int main()
{
//	char* str="123.234";
	char str[255];
	gets(str);
	printf("\n%d\n",isRealNumber(str));
	return 0;
}