C :: How To Loop Back To The Beginning Of Function

I am writing another program and I cannot find for the life of me how to loop the program back to the start of a function.

Code:
#include <stdio.h>
#include <stdlib.h>
int main(void) {
int choice;
char band1, band2, band3, band4;
printf ("This program calculates the resistor value based on the colours of the wire.
(enter the integer near the command)
");
printf ("What would you like to do?

[Code].....

This is my current iteration of the program. Obviously, I haven't finished writing the case 1 of the first switch, but for the other ones. I thought that return main would cause the program to loop back to the beginning after executing the case, but I see that it is not the case (pun not intended). Anyways, what would I have to insert to cause the program to loop again (other than for case 3)? And another question, why is it that in scanf in the first case, the program only accepts two characters before finishing?