我需要一个要求用户输入图钉的功能，经过3次错误尝试后，他们编程终止

Question

I have to write an ATM program for a class, and i cant figure out how to make a function that will ask the user for a pin and if the pin is entered incorrectly three times the program will display an exit message then terminate.... this is what i have some far. I think my issue is i don't know the correct syntax to handle my issue.

I know i will need a for loop but not sure how exactly to construct it.

void validate_acc(){
     int user_acc_try;

     printf("Please enter your account number: ");
     scanf("%d", &user_acc_try);

     if(user_acc_try != account_number){
                     printf("You entered the wrong account number");
                     }
     else{
          printf("");
          }
}

void validate_pin(){
     int user_pin_try;

     printf("Please enter your pin number: ");
     scanf("%d", &user_pin_try);

     if(user_pin_try != pin){
                     printf("You entered the wrong pin number.");
                     }
     else{
          printf("");
          }
}

void validate(){
     validate_acc();
     validate_pin();
}

Secondly, since i can only post every 90 minutes might as well ask another question, I do not know how to make a function go back to the beginning of my program like for example say after an deposit, what is the logic i would need to use to have a function go back to the beginning of my main function. I know of goto labels , that didnt seem to work when i put it in front of my main function like so...

MAIN:
int main()

i would put goto main; in another function and i would get a.... Main is not defined error. I have read a few different questions on here about labels but cant find anything that helps, if someone could guide me in the right direction, you would be giving me a great deal of relief.

thank you in advance.

Answer 1

It's a good idea to write out a flow chart for things like this if you can't figure out how to do it in code.

Please do not use labels/goto in C. It's a nasty habit and it's not needed.

You know how to use if statements to make a decision; think about how you would use a while loop to try to make the same decision over and over again until something changes. For instance, in pseudo-code (because I don't want to do your work for you)

user_has_not_entered_correct_pin = true
retries_left = 3
while retries_left > 0 and user_has_not_entered_correct_pin:
get pin
if pin_is_not_correct(pin) retries = retries - 1
else user_has_not_entered_correct_pin = false
end while

Answer 2

I am limited on time right now, so I will just post a quick help. I would suggest start researching loops in C. Since this is for a class, the book you are using should have information in it about for loops and while loops, but if not, a simple Google search can help a lot.

With a quick search on Google, this site seemed like a decent site for basic information on loops: Loops in C

It has links and examples of using a for loop, a while loop, a do...while loop and nested loops which should help you solve your problem.

Edited to add: In your post you mentioned that you think the problem is that you don't know the syntax that you need. It is for that reason that I pointed you to a location that can help you with the syntax that you need to solve your problem rather than show you directly how to solve the problem. I hope that this helps you not only with this question, but going forward in your class as well.

Answer 3

Keep a count variable like I have did below and check the number of attempts: I don't see a need for goto here. The same logic can be used for checking pin also.

int i=0;
while(1)
{
  if(i>2)
  {
    printf("Maximum attempts reached\n");
    break;
  }
  printf("Enter the acc_num\n");
  scanf("%d", &user_acc_try);
  if(acc_num == saved_acc_num)
  {
    // Do your stuff
  }
  i++;
}

Answer 4

Return value from validate_pin() int validate_pin(){... return 0; .... return 1;} int validate_pin(){... return 0; .... return 1;} and test it in the main() or your validate().

int i=0;
int result=0;
while ( (result==0)&&(i<3) ){
  result=validate_pin();
  i++;
}

Dont use goto , learn to use loops.