OJ Board

[cpp]
why did I get a runtime error?

/* @begin_of_source_code */
/* @JUDGE_ID: 27962FX 494 C++ */
#include<stdio.h>
#include<string.h>
int main()
{
char sen[100];
int a=0,b,count=0;
while(scanf("%c",&sen[a])!=EOF)
{
if(sen[a]=='\n')
{
a=0;
do
{
if(sen[a]==' '||!(sen >='a'&&sen <='z'||sen ...