Combined loops not working in Arduino - loops

Question

I have an arduino code which is doing tasks like this:
while (a=='A')
{
//do the task A
}
while (a=='B')
{
//do the task B
}
These loop run correctly when they are run separately. But the problem comes when I try to combine both loops i.e.
void loop ()
{
while (a=='A')
{
//do the task A
}
while (a=='B')
{
//do the task B
}
}
Below is the code in full details:
void loop()
{
////// admin
Serial.println("A or B");
delay(500);
char a = userinput();
delay(500);
while(a== 'A'){
Serial.println("Type Your Starting ID Number...");
while(1 ){
while (Serial.available()==false);
char e = Serial.read();
if(isdigit(e)==false) break;
startid = (startid*10)+(e - 48);
}
if(startid<=endid){
for(pageid=startid; pageid<=endid; pageid++)
{
Serial.print("Your Biometric ID # is ");
Serial.println(pageid);
delay(2000);
fingerenrollment(pageid);
delay(2000);
if(pageid == endid){
Serial.println("......Memory Is Full....");
while(1);
}
}
}
else{
Serial.println("Wrong Entry.......Please Reset Your Device.....");
while(1);
}
}
////// user
while(a=='B'){
lcd.print("WELCOME TO iPoll");
delay(2000);
lcd.clear();
lcd.print("Place Your Thumb");
delay(2000);
lcd.clear();
tempid = '\0';
Serial.println("Place your Thumb For Authentication");
delay(500);
while(true){
ID = fingerauthentication();
delay(500);
if(tempid != '\0') break;
}
delay(100);
resp = userinput();
delay(100);
lcd.clear();
datatrans(ID, resp);
}
}
If you need any more help, I am here. Just comment.

Answer 1

You seem to be stuck in an infinite while loop. Try changing while(a=='A') and while(a=='B') to if(a=='A') and if(a=='B'). The void loop() method in Arduino automatically acts like an infinite while loop, looping through the code within it forever.

Answer 2

while (a == 'A') loop is never ending because you never change the value of a. You need some a = something; somewhere in your code, or do what #Dan12-16 said. The same applies to 'B'.
And a couple of tips to make your code easier to read (in my opinion). Instead of using if (condition == false), you could use if (!condition). Choose while (1) or while (true), but don't mix them (I would choose the second one).