Thread: Problem with function. Please help!

Well, here's a repaired version --

The main problem is that you can't call an earlier function and think that you're "starting over" ... you're going to return from that function, and then you get unexpected recursive side-effects. (Recursion is something to do on purpose or not at all.) [edit: actually I'm not so sure that the problem is related at all to recursion ... I'm still looking it over.] To solve that I kludged a loop in main() and added "fail" values to your functions. You should always return something when it's not a void function anyway.

I also didn't think the do...while's were very clear or efficient. Of course, you don't need to change those, I just provided an option.

Code:

#include <stdio.h>

double Get_Credit_Limit(void);
double Get_Acc_Bal(double);


int
main (void)
{
  double returned_credit_limit = 0,
    returned_account_balance;	

  while (1)
  {
    if ((returned_credit_limit = Get_Credit_Limit()) == 0)
      continue;
    if ((returned_account_balance
          = Get_Acc_Bal (returned_credit_limit)) == 0)
      continue;
    break;
  }
  printf ("\nBalance: $%.2f ... Limit: $%.2f\n\n",
      returned_account_balance, returned_credit_limit);
  return 0;

}/*---- end of main -----------------------------------*/


double
Get_Credit_Limit (void)
{
  int validate = 0;
  double credit_limit = 0;
	

  while (validate < 2)
  {
    printf("\nPlease enter the credit limit: ");
    scanf("%lf", &credit_limit);

    if ((credit_limit >= 500) && (credit_limit <= 20000))
      return credit_limit;

    printf ("\nMust be above 500 and less than 20000. "
        "Try again\n");
      ++validate;
  }
  printf("\nERROR: Too many errors, starting new customer.\n\n"); 
  return 0;

}/*---- end of Get_Credit_Limit ------------------------------*/
		

double
Get_Acc_Bal (double returned_credit_limit)
{
  double account_balance;
  int validate = 0;

  while (validate < 2)
  {
    printf("\nPlease enter your account balance: ");
    scanf("%lf" , &account_balance);

    if (account_balance < 0)
    {
      ++validate;
      printf("\nERROR: Balance cannot be negative. Try again.\n");
      continue;
    }

    if (account_balance > returned_credit_limit)
    {
      printf("\nERROR: Account balance too high, "
          "starting new customer.\n\n");
      return 0;
    }

    if ((account_balance > 0) 
      && (account_balance < returned_credit_limit))
    return account_balance;
  }
  printf("\nERROR: Too many errors, starting new customer.\n\n");
  return 0;
}

Originally Posted by richdb

I'm confused as to what you did in the body of main(), and how the functions are starting over.

The "continue" just goes back to the while loop if the function fails (I used zero as an arbitrary fail value). When both functions succeed, "break" exits the loop.

When I used Get_Credit_Limit in the third "if", in Get_Acc_Bal it works fine. It just wont work in the last "if".

Well, what you really want to do is start over if you don't get a good value, so the best idea is to just do that. I'm still not sure why that was broken in your version, though. You should be able to call Get_Credit_Limit() from there ... or maybe I'm just too tired to see the problem right now.

BTW, I didn't change that third "if" statement, but actually it's redundant since you've checked those conditions already.

Also, you don't really need to use "else" after a break or return ... if you're still there, then there you are

I presume you are asking about the following section...

Code:

  while (1)
  {
    if ((returned_credit_limit = Get_Credit_Limit()) == 0)
      continue;
    if ((returned_account_balance
          = Get_Acc_Bal (returned_credit_limit)) == 0)
      continue;
    break;
  }

If so, the 1 just evaluates to TRUE -- (0 is FALSE). Incidentally, I believe any positive value equates to TRUE).

Anyway, the line...

Code:

while (1)

... is often used in a program to repeat indefinately. In this case, it would try and repeat indefinately... but the repetitions will stop, if/when execution reaches the 'break' statement at the end of the while loop.

I hope that makes sense.

Eddie

I've tried running the program as posted by eerok.

It seems to be working as expected (as far as I understand it).

Just as an FYI, recursion is when a function calls itself as part of it's execution. This often helps us programmers by allowing us to break a hard problem into a series of easier problems.

For example, if you had to compute n factorial (which is n * n-1 * n-2 .... * 1), e.g. 6 factorial is 6 * 5 * 4 * 3 * 2 * 1... you could do this using recursion by saying that the solution for n factorial is actually the same as n * (n-1 factorial). Given this, we could write a recursive function to work out the factorial of a number like so...

Code:

int factorial(int n)
{
	if ( n == 1 )
	{
		return n;
	}
	else
	{
		return n * factorial(n-1);
	}
}

Notice that the factorial function calls itself :-) ... this is basically the definition of recursion.

Good luck with your programming work.

Eddie.

I thought that something that goes in a while's parenthesis would have to be a variable with the "value" of 1 or 0. Didn't know you could just stick the value itself in there without using a variable in it's place.

So if I put a 0 in there the loop should never run?

And thanks for the recursion explanation

If so, the 1 just evaluates to TRUE -- (0 is FALSE). Incidentally, I believe any positive value equates to TRUE).

Any number except 0 is true. 1, 34, 538985, -4, -354554, and 3333 are all true.

So if I put a 0 in there the loop should never run?

Precicely.

When I write a forever loop (which differs from an infinite loop; infinite loops are unintentional), I like to use a for loop:

Code:

for(;;) {

If the conditional expression is missing from a for loop, it is true.

I thought that something that goes in a while's parenthesis would have to be a variable with the "value" of 1 or 0. Didn't know you could just stick the value itself in there without using a variable in it's place.

It can be any valid expression. The operators (like <=) return a zero or a non-zero result, so code like

Code:

while(x < 10) {

evaluated to (if x is 4)

Code:

while(4 < 10) {

and since 4 is < 10, that's like

Code:

while(1) {

You can even have compilcated expressions that involve functions:

Code:

while((!end_of_file() && read_input()) || quit) {