are all of them needed?

<= contradicts error message. Can std be < 0? (fix everywhere)

"atleast" -> "at least" (fix everywhere)

you can combine all conditions in one if-statement

Thanks, I removed unnecessary ones.

No std cant be < 0.

In starting I wrote

if (std[i] == 0) {
}

but then it shows warning.
Comparing floating point with == or != is unsafe.

Hence I have used <=

you should do a floating point comparison like "std[i] < DBL_MIN" or use gsl_fcmp().