Thread: Beginner having difficulty spotting problem

Hey guys! First post here.

I'm a C newbie trying to put together a simple program that receives the net cost of a piece of equipment and computes the new and used sale price based on the input. I'm using NetBeans on a windows 10 machine.

The program runs, but it seems to select random numbers for the output. Can anyone spot the inevitably newbie error I'm making in my code?

Thanks!

Code:

#include <stdio.h>


 main () 
{
    double net,usedprice,newprice;
    const double markup = 0.18;
    const double taxrate = 0.06;
    const double useddisc = 0.50;


    printf("Please enter Vittitow's cost:\n");
    scanf("%d", &net);
    newprice = ((net * markup)+ net) + (net * taxrate);
    usedprice = (((net * markup) + net) + net * taxrate) * usedprice;
    printf("New Price: $%.1f\nUsed Price: $%.1f\n", newprice, usedprice);
    return 0;
    
}

I just noticed one problem—in my usedprice math (line 15), I multiplied the whole thing by itself. The last item in line 15 should be useddisc instead of usedprice.

Still, even with that fixed, with an input of 2500, my output looks like:

New Price: $0.0
Used Price: $0.0

You should find and read some documentation for the scanf() function. Using the incorrect format specifier for the type produces undefined behavior. The "%d" format specifier is not the correct specifier for double. Your compiler, if properly configured, should warn you about this kind of issue.

Jim

First of all, turn on and turn up your compiler warning level to the highest setting.

Without using command line arguments in main(), it should be defined as:

Code:

int main(void)
{
    /* ... */
}

You should always check the return value to scanf() to insure you received data.

"net" is defined as a double, but you are using a "%d" integer format specifier.

Code:

usedprice = (((net * markup) + net) + net * taxrate) * usedprice;

You are multipling by "usedprice", whish is uninitialized then assigning back to "usedprice"

"useddisc" instead???

Thanks for the responses. Rstanley, I noticed the multiplying by "usedprice" error and fixed that, thanks. I'm trying to find the proper specifier for a double. Is it "%.1f", or does double have its own specifier?

Originally Posted by Neverender!

Thanks for the responses. Rstanley, I noticed the multiplying by "usedprice" error and fixed that, thanks. I'm trying to find the proper specifier for a double. Is it "%.1f", or does double have its own specifier?

In scanf(), "%f" for a float, and "%lf" (ell-f) for a double.

Your book on the C programming Language, that you should have, should give you the correct format specifiers for all the data types.

Since you are on a Windows computer, you could also check out the 'man' page here for scanf().

Thanks so much! Fixing that made it run perfectly!