Hi there! Today’s challenge was to compute standard deviation of an array of data given the formula `$$\sigma = \sqrt{\frac{\sum_{i=0}^{N-1} (x_i - \mu)^2}{N}},$$`

where `$$\mu = \frac{\sum_{i=0}^{N-1} x_i}{N}.$$`

The first input to the program is `N`

and then `N`

integers are fed to the program in sequence. My solution is given below.

```
package main
import (
"fmt"
"math"
)
func mean(a []int) float64 {
n := float64(len(a))
sum := 0.0
for i := 0; i < len(a); i++ {
sum += float64(a[i])
}
return sum / n
}
func sigma(a []int) float64 {
mu := mean(a)
sum := 0.0
n := float64(len(a))
for i := 0; i < len(a); i++ {
x := float64(a[i])
sum += (x - mu) * (x - mu)
}
sigma := math.Sqrt(sum / n)
return sigma
}
func main() {
N := 0
fmt.Scanf("%d", &N)
// allocate memory
X := make([]int, N)
// read numbers from stdin
for i := 0; i < N; i++ {
fmt.Scanf("%d", &X[i])
}
y := sigma(X)
fmt.Printf("%.1f\n", y)
}
```

The problem I had this time was with HackerRank. On my computer I had a result, but their system was saying it had a different result. After that I ran it again on HackerRank using the option *custom input*, but with the same input that gave me a bad answer error, but this time the answer was ok. Bugs appear everywhere, right? I will submit it with another language, still thinking about it. I wrote something to them, hopefully they will fix this bug.

That’s all for today! Thanks for reading!