determining the proper loop to use - c

Question

I am trying to teach myself C. For fun and for my own development, I have created a code that prompts the user for a letter grade, then outputs the range of that letter grade. Here is what I have so far:
//Ted C. Lim
#include "stdio.h"
int main()
{
char grade;
printf("Enter a single character grade: ");
scanf("%c", &grade);
printf("You entered %c as the grade. ", grade);
switch(grade)
{
case 'A':
printf("The grade range for A and A- is 100%% - 90%%.");
break;
case 'B':
printf("The grade range for B and B- is 80%% - 89%%.");
break;
case 'C':
printf("The grade range for C and C- is 70%% - 79%%.");
break;
case 'D':
printf("The grade range for D and D- is 60%% - 69%%.");
case 'F':
printf("The grade range for F is 0%% - 59%%.");
default:
printf("That grade does not exist.");
break;
}
}
If you run the program, you will see that it asks the user only once, returns the proper output, then stops. What I would like to do is repeat the prompt indefinitely until the user inputs something like 'Q' to quit. I know I should use some sort of loop here, but I'm not quite sure how to apply it.

Answer 1

There a couple different options you could choose here, both the while and the do while loop would work. Personally, I would say that a do while loop would be better fit for this case, mostly because you know for sure that you want the program to prompt the user at least once. In order to use it you would need to place the do before the printf statements and then run while some scanf input at the end is != "Q"

Answer 2

You can use a while loop, along with another character case to exit out of the loop.
char grade;
while (1)
{
printf("Enter a single character grade (or 'X' to exit): ");
scanf(" %c", &grade);
printf("You entered %c as the grade. ", grade);
if (grade == 'X') // Or another letter, make it clear what you're using
{
break;
}
// Output code here...
}
I would also recommend you check for both lowercase and uppercase letters. In the switch statement:
case 'A':
case 'a':
printf("The grade range for A and A- is 100%% - 90%%.");
break;
In the if statement:
if (grade == 'X' || grade == 'x')
{
break;
}

Answer 3

To repeat an action indefinitely, you could wrap it inside a while loop with a condition that is always true (e.g., while (1) { ... }) as follows:
#include <stdio.h>
#include <ctype.h>
int main()
{
char grade;
while (1)
{
printf("Enter a single character grade (or Q to quit):\n");
scanf(" %c", &grade);
grade = toupper(grade);
if (grade == 'Q') break;
printf("You entered %c as the grade.\n", grade);
switch(grade)
{
case 'A':
printf("The grade range for A and A- is 100%% - 90%%.\n");
break;
case 'B':
printf("The grade range for B and B- is 80%% - 89%%.\n");
break;
case 'C':
printf("The grade range for C and C- is 70%% - 79%%.\n");
break;
case 'D':
printf("The grade range for D and D- is 60%% - 69%%.\n");
break;
case 'F':
printf("The grade range for F is 0%% - 59%%.\n");
break;
default:
printf("That grade does not exist.\n");
break;
}
}
return 0;
}
You'll notice I've made a few other modifications, which I'll run through here:
include "stdio.h" should really be #include <stdio.h>. The angle brackets tell the compiler to look in the standard directory for system header files.
I also added #include <ctype.h> because I'm using the toupper() function to convert the input character to upper case. This makes your code easier to use, because it will now accept both upper and lower case letters.
The scanf() format string includes a space before %c. This will skip over any white space characters including newline characters. Without it, the program would treat these characters as actual inputs and tell you that the \n grade does not exist.
The break statement can be used to exit the loop when the user enters Q. There were also a couple of breaks missing from your switch block.
The main() function is declared as int main() { ... }, so it should return an integer value. If no errors have occurred, this value should be zero.

Answer 4

Encase your switch case inside of a while loop that is true and it will run indefinitely. You can also use scanf to check for a specific key to be entered to stop it too.