为啥数组的长度写14就对，写13就错，长度不就该是13吗？我数错了吗？

#include<stdio.h>
int main(){	
	char s[14],c;int p = 0,j=1;
	scanf("%s",s);
	 p = ((s[0]-'0')*1+(s[2]-'0')*2+(s[3]-'0')*3+(s[4]-'0')*4+(s[6]-'0')*5+(s[7]-'0')*6+(s[8]-'0')*7+(s[9]-'0')*8+(s[10]-'0')*9)%11;
	if(p == s[12]-'0'||(p==10&&s[12]=='X')){
		printf("Right");
	}else{
		if(p == 10){
			s[12] = 'X';
		}else{
	 		s[12] = p+'0';	
		}
		printf("%s",s);
	}
	return 0;
}