#include <iostream>
#include <cmath>
using namespace std;
float standard_deviation(float data[], int n);
int main()
{
    int n, i;
    float data[100];
    cout << "Enter number of data: ";
    cin >> n;
    while (n>100 || n<=0)
    {
        cout << "Error! number should in range of (1 to 100)." << endl;
        cout << "Enter the number of data again: ";
        cin >> n;
    }
    cout << "Enter elements: " << endl;
    for(i=0; i<n; ++i)
        cin >> data[i];
    cout << endl;
    cout << "Standard Deviation = " << standard_deviation(data,n);
    return 0;
}
float standard_deviation(float data[], int n)
{
    float mean=0.0, sum_deviation=0.0;
    int i;
    for(i=0; i<n;++i)
    {
        mean+=data[i];
    }
    mean=mean/n;
    for(i=0; i<n;++i)
    sum_deviation+=(data[i]-mean)*(data[i]-mean);
    return sqrt(sum_deviation/n);          
}

Output:

Enter number of data: 6

Enter elements: 

2

3

1

6

4

5

Standard Deviation = 1.70783