expression error:property or method named in class array is missing or does not exist.

hi,my friends,

I from china,

it is unfortunately,my english is poor.

so,there are many mistake in this post.

like this,words or grammar is wrong.

I am sorry.

I meet an expression error:property or method named in class array is missing or does not exist.

It saids:

=================================

after effects warning:

expression disabled.

error at line 35 in porperty 'source text' of layer 1(bfs) in comp 'biaodashibenfen 2'.

property or method named '0' in class 'array' is missing or does not exist.

it may have been renamed,moved,deleted,or the name may have been mistyped.

==================================

please look the picture.

expression is below the==============

==============

l=thisComp.layer("peilai");

ain=0;

bout=100;

p=l.transform.position;

c=bout-ain;

dqz=time/thisComp.frameDuration;

ps=[];

mzjls=[];

dqjls=[];

bfs=[];

    if(dqz<ain){

    idq=0;

}

if(dqz>bout){

    idq=0;

}

else{

idq=dqz-ain;

for (i=0; i<=c; i++) {

    d=(ain+i)*thisComp.frameDuration;

    ps=p.valueAtTime(d);

    if(i>=1){

    mzjls=length(ps[i-1], ps);

    dqjls=dqjls[i-1]+mzjls;

}

else{

    mzjls=0;

    dqjls=0;

}

}

for (i=0; i<=c; i++) {

    bfs=100*(dqjls/dqjls);

}

}

bfs[idq].toString();

===========================

the line 35 :

bfs[idq]

maybe is wrong.

But I dont know why is wrong?

How can I fix it?

Thanks a lot!