Index exceeds matrix dimensions.

Index exceeds matrix dimensions.
>> disp('');
disp(' ');
n=input('请输入所要测试的随机数长度：')
k=0;b=0;c=0;d=0;e=0;f=0;g=0;h=0;l=0;j=0;
for t=1:100
a=rand(1,n)
sum=0
for i=1:n
sum=sum+2*b(i)-1;
end
Sobs=abs(sum)/sqrt(n)
p=Sobs/sqrt(2)
p_value=erfc(p)
if(0