# simple question

• 10-20-2003
lwong
simple question
Dear All,
I want to have a code with a formula
N-1 N-1
aut[m]=summation x(n)x(n+m)
n=0 n= 0
if I have code like

Code:

```for (m=0;m<N;m++) {       for (n=0;n<N;n++)           {               aut[m]+=x(n)*x(n+m);           } }```
will this work?
• 10-20-2003
VegasSte
Have you tried it in a c compiler?
It seems sound enough!
• 10-20-2003
lwong
Yes, I have complied it, no any error, but the results are out of my expectation. say x(n) is a sequence like:
Code:

`x(n)={1.0,2.0,3.0,3.5}, and N=4.`
when the program runs at some points, take an example , x(5) (when n=3,m=2), the program dont know what value x(5) is? it will return me a radom number which is not i want. How can I solve this problem?
Thank you.
• 10-21-2003
WaltP
Quote:

Originally posted by lwong
Yes, I have complied it, no any error, but the results are out of my expectation. say x(n) is a sequence like:
Code:

`x(n)={1.0,2.0,3.0,3.5}, and N=4.`
when the program runs at some points, take an example , x(5) (when n=3,m=2), the program dont know what value x(5) is? it will return me a radom number which is not i want. How can I solve this problem?
Thank you.

Whithout code to look at, we can only guess. And my guess is that you've defined x to be an array of 5 values, which means x(0) thru x(4). x(5) does not exist so you are looking at random data outside your array.