What is wrong with my calculations in my program?

Question

0.00/5 (No votes)

See more:

Im not quite sure where in my code is causing the problem that causes wrong calculations. When I run the program there is a warning of : C4305: 'argument' : truncation from 'double' to 'float'. There seems to be something wrong with Tax amount(ta) and Total cost(tc), Thanks.

Current Output:
Cost before Tax: $30.20
Tax Amount: $30.20
Total Cost: $-107374144.00
ground beef is ex-sponged
Press any key to continue . .

What it **should** be:
Your item name:ground beef
Cost before Tax: $30.20
Tax Amount: $2.64
Total Cost: $32.84
ground beef is ex-sponged

C++

#define _CRT_SECURE_NO_WARNINGS
#include<iostream>
#include<iomanip>
#include<string>

using namespace std;

class item
{
public:
    item(char* = " " ,float=0.0,int=0,float=0.0);
    ~item();
    void print();
    void calc(int);
private:
    char name[20];
    int quan;
    float cost, tp, cbt, tax, tc;
};
item::~item()
{
    cout << name << " is ex-sponged"<<endl;
    system("pause");
    }
item::item(char *w,float x, int y, float z)
{
    strcpy(name, w);
    cost = x;
    quan=y;
    tp = z;
    tax=cost*quan;
    tc=cbt+tax;
    cbt = cost*quan;
}
void item::print()
{
    cout << "Your item name:" << name << endl;
    cout << "Cost before Tax: $" << cbt << endl;
    cout << "Tax Amount: $" << tax << endl;
    cout << "Total Cost: $" << tc << endl;
}

void item::calc(int n)
{
    quan += n;
    cbt = cost*quan;
     tax = cbt*tp/100;
     tc = cbt + tax;
}

int main()
{
    item i("ground beef", 7.55, 4, 8.75);
    cout << setprecision(2) << showpoint << fixed;
    i.print();
}

Posted 29-Oct-14 23:21pm

Member 11192223

Updated 29-Oct-14 23:31pm

DaveAuld

v2

Add a Solution

3 solutions

Solution 3

Without knowing what exactly is looking like is behaving badly and what's supposed to happen it's a bit hard to work out what's going wrong. However here's some suggestions to make things a bit easier to read:

- you don't need a fixed size character buffer and it's far easier to use std::string

- use member initialisers - it'll make your constructor less cluttered

- use descriptive names. x, y and z don't tell me as a reader what the bits and pieces are supposed to represent or do. I can't even guess what tc and tp are. item looks like a line_item (it has a quantity) and calc isn't calc it's add_items_to_line if I'm reading what it does properly.

- fix warnings. As you didn't say what was giving you a warning I can't provide a lot of guidance there - although I'd hazard a guess it's when an int is implicitly promoted to a double, used in a calculation and the result stashed back in a float.

Anyway, fix that lot and if the problem doesn't leap out you step through it all with a debugger and see what isn't being set the way you expect. Next time consider investigating test driven development which is a really great way to avoid calculation problems before they get too heavily ground into the carpet.

Posted 29-Oct-14 23:58pm

Aescleal

Solution 1

I suppose you mean that you get a compilation error.

Try to change your code in the main() function to this:

C++

item i("ground beef", 7.55f, 4, 8.75f);

and also the declaration of the constructor

C++

item(char* = " ", float = 0.0f, int = 0, float = 0.0f);

The f after a number is used to say that it is float.

(Spaces are not evil, in the right places they actually help to make the code readable.)

Posted 29-Oct-14 23:44pm

George Jonsson

Updated 29-Oct-14 23:49pm

v3

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Garth J Lancaster · Accepted Answer · 2014-10-29T23:53:00

Solution 2

in addition to George's comments

C#

tc=cbt+tax;
        cbt = cost*quan;

how can tc = cbt + tax, when you havnt calculated cbt yet ? - so reverse those two lines so ..

C#

cbt=cost*quan;
               tc=cbt+tax;

Posted 29-Oct-14 23:53pm

Garth J Lancaster