括号匹配

#include<stdio.h>
#include<string.h>
typedef struct bracket
{
	char bra[100];
	int num;
} bracket;

int main()
{
	bracket b;
	b.num=0;
	int i;
	char a[100];
	gets(a);
	for (i=0;i<strlen(a);i++)
		{if((a[i]=='{')||(a[i]=='[')||(a[i]=='('))
			{
				
				b.bra[b.num]=a[i];
				b.num++;
				
				}
		else if((a[i]=='}')||(a[i]==']')||(a[i]==')'))
		{
				
				switch(a[i])
					{
					 case '}':
					 if (b.bra[b.num-1]=='{')
					 b.num--;
					 else b.num++;
					 break;
					 case ']':
					 if( b.bra[b.num-1]=='[')
					 b.num--;
					  else b.num++;
					 break;
					 case ')':
					 if (b.bra[b.num-1]=='(')
					 b.num--;
					  else b.num++;
					 break;					 	
					}
				}
				}
	if (b.num==0)
	{printf("括号配对\n");}
	else printf("括号不配对\n");	
	return 0; 
}