Problem converting a double to a char

[joey0xx]

Hi, I'm trying to make this code know if the value I'm entering for n is a
letter and give me an error whenever I do so, but I'm having trouble with it.

I'm sure I have to convert the n to a char, but I'm not sure what to do since all I can think of is doing ch=static_cast<char>(n);.

Whenever I do that either the menu shows up, but doesn't let me do anything else or it says n wasn't initialized, depending on where I put it.

Edit:Didn't add the rest of the code because I didn't think it was necessary...

double n, boot total=0; 
char select, ch;
bool flag=false;

do
{
cout<<"\t\t\tMENU PRINCIPAL"<<endl;

do
{
cout<<"-------------"<<endl;
cout<<"-------------"<<endl;
cout<<"Select a case: ";
cin>>select;


switch(select)
{
case '1':
  if (flag == false)
  {
  system("cls");
  cout<<"You're in Case #1..."<<endl;
  cout<<"Enter N before proceeding = ";
  cin>>n; 
  boot=n;
  cout<<"Continue by pressing Enter"<<endl;
  system("pause");
  flag=true;
  }
  else if(n >= 'A' && n <= 'Z')
  {
  cout<<"You should only enter a numeric value for n"<<endl;
  cout<<"Enter another value for n."<<endl;
  cin>>n;
  flag=false;
  }
  else(n >= 'a' && n <= 'z')
  {
  cout<<"You should only enter a numeric value for n"<<endl;
  cout<<"Entre el valor de n de nuevo."<<endl;
  cin>>n;
  flag=false;
  }
  system("pause");
  }
  n=boot;
  break;

case '2':
  if (flag == true)
  {
  cout<<"Serie #1 (OPCION 2)"<<endl;
  for (n; n<=100; n++)
  {
  total +=(pow(-1.0, n-1))*(((2*n)+(1))/(n*(n+1)));
  cout<<"n = "<<n<<" sumatoria= "<<total<<endl;
  }
  cout<<"Result of Serie #1 = "<<total<<endl;
  cout<<"Continue by pressing Enter"<<endl;
  system("pause");
  }
  else
  {  
  system("cls");
  cout<<"Go to Option #1 1st!!! "<<endl;
  system("pause");
  }
  n=boot;
  total=0;
  break;
}
}while(select != '1' && select != '7');
}while(select == 1);

I know I'm not doing anything with the ch in that code.
Any ideas?

[giblit]

why the heck are you trying to make a double into a char? chars are ints. There is no char for 2.5 only for 2 and 3. Also singed chars are -127 - 128 or signed chars from 0 - 255. Also doubles are not precise 4 could really be 3.9999999999999 or 4.000000000000000000001 so just change from double to int. Also, you do not need to do static cast try this

int i = 60;
char ch = i;

P.S. system("anything"); isn't the best practice.

[joey0xx]

In this case i would be n right? Since this is an assignment I have to specifically enter the value of n in the cmd. What I'm trying to do is, whenever I enter a letter from a to z it gives me:

 
cout<<"You should only enter a numeric value for n"<<endl;
cout<<"Enter another value for n."<<endl;

So if I put a numeric value to n, i this case 60, I wouldn't be testing anything...

[giblit]

Mine was just an example and yeah just make n an int instead of a double.

[joey0xx]

Just edited the code. Sorry I didn't add it sooner, I didn't think it was necessary but I put it now just to know exactly what we're dealing with.

Made the n an int but i have this in another case:

total += (1)/((n*(sqrt(n+1.0)))+(n+1)*(sqrt(static_cast<double>(n))));

Did what you told me but I get this output:

1 2 3 4 5 6 7 8 9 10 11 12 13

Estas en la Opcion #1... Enter N before proceeding = b Continue by pressing Enter Press any key to continue . . . MENU PRINCIPAL 1.) Validate n 2.) Serie # 1 3.) Serie # 2 4.) Serie # 3 5.) Serie # 4 6.) Serie # 5 7.) Exit

------------- Select case: Press any key to continue . . .

Where it says "Select case" that's where I'm supposed to enter the number of the case i want to switch to but instead I get that output...