Need to loop switch statement until 1 or 2 is entered - c

Question

I need to loop the switch statement until 1 or 2 is entered as an input. Any help would be nice or sample code. I tried to use a while loop and it kept crashing. I tried a do while as well and it turned into an infinite loop so I must be doing something wrong.
int main (void)
{
int choice; // choice to run program from start menu or quit
while (1)
{
// Menu for entering resistor and capacitor values
printf("Welcome to the 555 Timer Frequency and Duty Cycle Calculator\n");
printf("Please enter two resistor values in between ");
printf("1 kOhms and 100 kOhms and a capacitor value\n\n");
//Start of menu
printf("Menu\n\n");
printf("1. Continue\n");
printf("2. Exit\n");
scanf("%d", &choice); // User inputs value
switch (choice)
{
case 1:
resistor(); // Program resistor is run if 1 is input
break;
case 2:
printf("Goodbye."); // Program ends if 2 is input
break; // break is used to exit while loop
default:
printf("Sorry I do not understand\n\n");
fflush(stdin); /* clears input buffer to allow user to input a new value if anything other
than 1 or 2 is input into scanf */
}
break;
}
return 0;
}

Answer 1

The problem is that you have a "break" right at the end of your "while", so it's only executed once.
It has been a long time since I did program in C, but if I remember correctly you should avoid using "fflush()" since it has an undefined behavior. Instead, you can change your "scanf()" to be something like:
scanf(" %d", &choice); // User inputs value
That way, you have the same supposed effect of the "fflush()" at the same time of having a cleaner code.

Answer 2

You can use this code
for(;;) {
// Menu for entering resistor and capacitor values
// Start of menu
// User inputs value
if(choice == 1) { ... break; }
else if(choice == 2) { ... return 0; } // If you use the break,the for loop will be stopped or You can use return 0; to return the whole function
else { ... break; }
}
or, also you can use this code
for(;;) {
switch(choice ) {
case 1: ... break;
case 2: ... return 0; // If you use the break, only switch statement is stopped. You can use return 0; to return the whole function
default: ... break;
}
}
Edit :
#include <stdio.h>
int main (void)
{
int choice; // choice to run program from start menu or quit
// Menu for entering resistor and capacitor values
printf("Welcome to the 555 Timer Frequency and Duty Cycle Calculator\n");
printf("Please enter two resistor values in between ");
printf("1 kOhms and 100 kOhms and a capacitor value\n\n");
while (1)
{
//Start of menu
printf("Menu\n");
printf("1. Continue\n");
printf("2. Exit\n");
scanf("%d", &choice); // User inputs value
switch (choice)
{
case 1: // Program resistor is run if 1 is input
break;
case 2: printf("Goodbye."); // Program ends if 2 is input
return 0; // return 0; is used to exit while loop
default: printf("Sorry I do not understand\nStart Again !\n");
// fflush(stdin); /* clears input buffer to allow user to input a new value if anything other than 1 or 2 is input into scanf */
break;
}
printf("\n");
}
return 0;
}