Help!!!questions about a circuit program..

Can someone please help me solve the following problems for my mini project? Your help will be highly appriciated...
1. The function frontpage(name) can't be linked to the other 2 functions.
2. If user mis-enter a character for switch case, a infinite loop will occur.(same case happened for cin>>number_resistor in my project)

Code:

void resistor_knowledge(void frontpage(char name[50])){
     system("color 4E");
     ifstream resistor_file("resistor.txt");
     char k_resistor[max_letter];
     for (int size=0; size<=20; size++){
     resistor_file.getline(k_resistor,max_letter);
     cout<<k_resistor;
     cout<<"\n\nPRESS ANYKEY TO RETURN TO MAIN MENU.";
     getch();
     frontpage(name);
     }
     }
     
void capacitor_knowledge(void frontpage(char name[50])){
     system("color 4E");
     char k_capacitor[max_letter];
     ifstream capacitor_file("capacitor.txt");
     for (int size=0; size<=20; size++){
     capacitor_file.getline(k_capacitor,max_letter);
     cout<<k_capacitor;
     cout<<"\n\nPRESS ANYKEY TO RETURN TO MAIN MENU.";
     getch();
     frontpage(name);
     }
     }

void frontpage(char name[50]){     int choice,x; 
     repeat_main:
     system ("COLOR 3A");
     cout<<"\n Hello, "<<name<<".\n Welcome to this CIRCUIT PROGRAM!!\n\n";
     printf(" 4.Resistance in a circuit\n 5.Capacitor in a circuit\n ");
    cin>>choice;
    system("CLS");
    
    switch (choice){
           
           case 1:
                resistor_knowledge();
                break;
           
           case 2:
                capacitor_knowledge();
                break;


           default:
                   {
           cout<<"\n\n\n                                 INVALID INPUT!!\n\n                            ENTER A VALID INPUT PLEASE!!!";
         time(x=3);
         system("CLS");
         
         goto repeat_main;
                
                }
                }
}
int main(){
    char name[50];
    cout<<"Please enter your name:";
    cin.getline(name,50);
    system("CLS");
    frontpage(name);

First, delete lines 10 and 23.
You'd get back to frontpage() simply by returning - not by calling it recursively.

Then replace your goto repeat_main; with a while loop.

> time(x=3);
What's this supposed to do?

Also, get rid of all those system(cls) and system(color) calls until the whole thing is working.
They're just candy distraction until the program is working.

Returning??how to return??can u give me an example?thanks...
The time(x=3) is just another function which i didn't include when copying.
& thanks again for your suggestion...i'll remove those things until my program run properly^.<