这个程序有问题么？老是WA

#include <stdio.h>
char letter[25];
int a[]={-1,1,2,3,-1,1,2,-1,-1,2,2,4,5,5,-1,1,2,6,2,3,-1,1,-1,2,-1,2};
int main(int argc, char* argv[])
{
	char *p;
	int last=-1;
	while(scanf("%s",letter)!=EOF){
		p=letter;
		while (*p) {
			if( a[*p-'A']>0 ){
				if(a[*p-'A']!=last)
				{
					printf("%d",a[*p-'A']);
					last=a[*p-'A'];
				}
			}else{
				last=-1;
			}
			++p;
		}
		printf("\n");
	}
	return 0;
}