按照乒乓球的11分制和21分制输出比例。求大神指教哪里有问题

#include<stdio.h>
#include <string.h>
void output(char* a, int n)
{
    int i;
    int b, c;
    b=c=0;
    for(i=0; a[i] != 'E'; i++)
    {
        if(a[i]=='W')
            b++;
        if(a[i]=='L')
            c++;
        if((b>=n && b-c>=2) || (c>=n && c-b>=2))
        {
            printf("%d:%d\n", b, c);
            b = c = 0;
        }
    }
    if(b != 0 || c != 0)
        printf("%d:%d\n", b, c);
}
int main()
{
    char a[200], b[31];
    int len;
    while( gets(b)!=NULL )
    {
        strcpy(a, b);
        len = strlen(b);
        while( b[len-1]!='E' )
        {
            gets(b);
            strcat(a, b);
            len = strlen(b);
        }
        output(a, 11);
        printf("\n");
        output(a, 21);
        printf("\n");
    }
    return 0;
}