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.

Answer 1

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)