break program

hi, I’ve got a task home and I have a little problem how can I give a command at which somebody who use this program

can break it at any time he want just by pressing 'E'? I know

that it supposed to be with –while- but I don’t know where to put it

this code supposed just to convert units between fahrenheit to clesius.

thanks. my code is

#include <stdio.h>
int main()
{
    float num1,num2;
    char unit;
 
    printf("Enter the unit of value (f or c)- end with E\n");
scanf("%c" , &unit);
while(unit=='c' || unit=='f ')
    {
        printf("Incorrect unit entered.please enter again \n");
        scanf("%c" , &unit);
     }
if(unit=='c')                             /*celsius to Fahrenheit*/
{
    printf("enter celsius degree\n");
    scanf("%f",num1);
    num2=9/5*num1+32;
    printf("your choise is %f \n",num1);
    printf("in Fahrenheit is %f\n",num2);

}
else
    if(unit=='f')  //*Fahrenheit to celsius*//

{                              
printf("enter Fahrenheit degree\n");
scanf("%f",num1);
num2=5/9*(num1-32);
printf("your choise is %f\n",num1);
printf("in celsius is %f\n",num2);
}

return 0;
}