ANSI C: Error checking user input with a function

Question

I am attempting to use a single error checking function to check for errors within multiple other functions. However, When running the program, it gets stuck in a loop and won't break from it. Once the application gets a valid input, it should continue to the next function. However it repeats the fStartBalance function even if the error checking returns a 0. I'm kind of a beginner, so I'm not too good at troubleshooting. Here is the applicable code:

/* Begin fValidateFloat */
int fValidateFloat(float input, float minValue, float maxValue)
{
    int failed = 0;

    while (input < minValue)
    {
        printf("\nError: Input too low, please enter a value greater than or equal to %.2f.", minValue);
        failed = 1;
        return failed;
    }
    while (input > maxValue)
    {
        printf("\nError: Input too high, please enter a value less than or equal to %.2f.", maxValue);
        failed = 1;
        return failed;
    }
} /* End fValidateFloat */

/* Begin fStartBalance */
float fStartBalance(void)
{
    float startBalance; /* Declare variable */
    int failed;

    while (failed = 1)
    {
        printf("\n\nNow enter your current balance in dollars and cents: "); /* Prompt user to input current balance */
        scanf("%f", &startBalance);
        fflush(stdin);
        failed = fValidateFloat(startBalance, 0, 3.4e+38);
    }

    return startBalance; /* Return variable */
} /* End fStartBalance */

Thanks for any help.

Look at the while loop: you want to check if failed is equal to 1. Instead, though, you are setting it to 1! Use failed == 1 instead. — ravron
– ravron, Commented Dec 2, 2014 at 2:00
Remember to turn all your warnings on. At the very least use -Wall if you are using gcc. It will warn you about silly mistakes like your failed = 1 typo. — JS1
– JS1, Commented Dec 2, 2014 at 2:16
the 'while' statements in function: fValidateFloat never execute in a loop, so would be better written as 'if' statements — user3629249
– user3629249, Commented Dec 2, 2014 at 4:05
regarding that (previously commented) while loop by @Riley, the variable 'failed' is not initialized to any specific value (just what ever happens to be on the stack at that address. Suggest: set the 'failed' variable to some known value when declaring it. this is also a prime example of why the literal should be on the left side, so the compiler would catch these kinds of errors, so you don't have to. — user3629249
– user3629249, Commented Dec 2, 2014 at 4:07
the call to scanf needs attention for: 1) the format string needs a leading ' ' to consume white space, like the prior newline 2) the returned value needs to be checked to assure the operation/format conversion(s) was successful — user3629249
– user3629249, Commented Dec 2, 2014 at 4:10

2501 · Accepted Answer · 2014-12-02 02:09:17Z

2

fflush(stdin); is undefined

You never return any value from fValidateFloat() in the case the while statements are not taken:

        return failed;
    }
} /* End fValidateFloat */

In the same function while loops don't make any sense, use an if statement instead:

while (input < minValue)
{
    printf("\nError: Input too low, please enter a value grea%.2f.", minValue);
    failed = 1;
    return failed;
}

You are setting failed to 1 in the while loop, instead of comparing it to 1:

while (failed = 1)

edited Dec 2, 2014 at 2:09

answered Dec 2, 2014 at 2:01

2501

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