validation - Validating a double in c++ -

i'm new coding, please keep in mind before commenting.

so i've been trying coding while, , today went library , picked book called "programming in c++". i've written basic programs, have gotten stuck @ 1 point, have no idea how create function makes sure when user prompted double, enter valid. (if user enters character 'k', program breaks). searched here , on net, , there answers, more along line of "here's line of code works, insert x, y, z, it". , don't have enough experience know do. here sample mix of code question, , me failing try make work in program:

#include <iostream> #include <stdio.h>   using namespace std;  double getdouble () {     double x;     cin >> x;     int valid = 0;     while (valid == 0) {         if (x == double) {       return x;       break;   } else if (x != double) {       cout << "invalid input! please input numerical value." << endl;       cin.clear();       while (cin.get() != '\n') ; // empty loop     } } return x; } 

now want use "cin << x" user input x, , make sure x double, , i'm failing quite hard @ this. if explain in manner clarifies each operation, grateful. example, don't know break function does, , cin.clear(), , cin.get() do. (i know duplicate, answers on other question not @ address i'm confused about, thank taking time read & answer this! :)

this seems close analog code (mostly) works:

double getdouble () {     double x;     cin >> x;     // ver1: while( cin.fail() ) // or !cin.good()   no trailing char check.     while( cin.fail() || (cin.peek() != '\r' && cin.peek() != '\n'))     {         cout << "invalid input! please input numerical value." << endl;         cin.clear();         while( cin.get() != '\n' ); // or cin.ignore(1000, '\n');         cin >> x;     }     return x; }