c++ Straustrup calculator02.cpp function Error - function

Question

I have a small problem with the functions inside calculator02.cpp
there is an error when compile the code
warning: control reaches end of non-void function [-Wreturn-type]130 | }
Yes I know that in any case function must return the value what can I do to solve this problem? in this case I do not have any more cases apart from that ones inside the function itself, same with the get function;
Token Token_stream::get()
{
if (full) { // do we already have a Token ready?
// remove token from buffer
full = false;
return buffer;
}
char ch;
cin >> ch; // note that >> skips whitespace (space, newline, tab, etc.)
switch (ch) {
case ';': // for "print"
case 'q': // for "quit"
case '(': case ')': case '+': case '-': case '*': case '/': case '}': case '{':
return Token(ch); // let each character represent itself
case '.':
case '0': case '1': case '2': case '3': case '4':
case '5': case '6': case '7': case '9':
{
cin.putback(ch); // put digit back into the input stream
double val;
cin >> val; // read a floating-point number
return Token('8', val); // let '8' represent "a number"
}
default:
error("Bad token");
}
}
double primary()
{
Token t = ts.get();
switch (t.kind) {
case '(': // handle '(' expression ')'
{
double d = expression();
t = ts.get();
if (t.kind != ')') error("')' expected");
return d;
}
case '{':
{
double d = expression();
t = ts.get();
if(t.kind != '}') error("'}' Expected");
return d;
}
case '8': // we use '8' to represent a number
return t.value; // return the number's value
default:
error("primary expected");
}
}