Need Help With Square Root Function

[techwonder]

I have been hacking at this for days and the issue is our professor is not letting use cmath.

So his instructions for calculating the square root is to use a certain formula and I cant get it to work. It is defined at the bottom as a function called sqrt

I can enter values and get the variance but i dont see how to 'join' the 2 sections and to have this function calculate the square root of the variance.

  #include<iostream>

using namespace std;

double sqrt(double value);
int main()
{
    int n = 0 ;                         //enter number of values
    char c = 'y';
    while(c == 'y' || c == 'Y')                     //while it is a yes to run the loop
    {

        while(n > 100 || n <= 0)
        {
            cout<<"How many values do you wish to enter? (Less than 100)"<<endl;         //enter number of numbers to enter
            cin >> n;
        }
        int i = 0;
        int array[100];
        while(i<n)
        {
            cout<<"Enter number "<<(i+1)<<endl;                            //enter numbers
            cin>>array[i];
            i++;
        }
        double  mean = 0;
        for( i = 0; i<n ; i++)
        {
            mean += array[i];                                       //add all values
        }
        mean /= n;                                                      //find mean

        double variance = 0;
		double std_dev = 0;
        for( i = 0; i<n ; i++)
        {
            variance += (array[i] - mean)*(array[i] - mean);                 //calculate sum of squares
        }
        variance /= n;                                                          //calculate variance
        std_dev = sqrt(variance);                                                //get sqrt of it to get standard deviation

        cout<<"Variance: "<<variance <<" and  Standard deviation: "<<std_dev<<endl;
        cout<<"Do u wish to continue? Enter 'y' or 'Y' for yes and 'n' or 'N' for no"<<endl;
        cin >> c;

    }
}
double sqrt(double value)
{
    double new_value;
    double old_value = 1;                               //set seed to 1 initially
    new_value = 0.5*(old_value + (value/old_value));        //set new value using this formula
    while(new_value - old_value >= 0.005)                   //while difference netween new value and old value >= 0.005
    {
        new_value = 0.5*(old_value + (value/old_value));            //keep calculating new_value
        old_value = new_value;                                      //set old_value to this new value
    }
    return new_value;

}

[shadowCODE]

So his instructions for calculating the square root is to use a certain formula and I cant get it to work

Are u saying you get errors when using that function? or is that that the function is not correct??

i dont see how to 'join' the 2 sections

which 2 sections?

and to have this function calculate the square root of the variance.

I thought this is what you did in line 40. std_dev = sqrt(variance);

[techwonder]

yes, the variance works but the std deviation is not calculating properly. I am getting a large number.

So basically line 40 is calling the sqrt function but not giving me a proper answer.

If I try to use the variance variable in the sqrt function, the compiler calls an error as it is only defined in the Main function. That is what I mean by tying the 2 together.


I think that makes sense

[techwonder]

so upon further inspection the formula seems to just be returning a value half of the variance, not the square root. However the formula came from the teacher.