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It works...but that can't be!Code:float round(float n){
if ((n / 10)>=0){
n--;}
return n;
}
I swear, it's working perfectly for me... 14.5 evaluates to 15, and 14.45 evaluates to 14.
Say we passed in 14.5, though. 14.5/10 = 1.45, which IS greater than 0. In fact, it's ALWAYS going to be > 0 unless you pass in a negative number. So 14.5 should return 13.5...not 15...what the hell?
And I assure you that there's no other function or anything getting in the way.
It's not working for me..
That's the output from this code:Code:15.35 | 14.35
15.55 | 14.55
Code:#include <iostream>
float round(float n);
int main()
{
float x = 15.35;
std::cout << x << " | ";
x = round(x);
std::cout << x << "\n\n";
x = 15.55;
std::cout << x << " | ";
x = round(x);
std::cout << x;
std::cin.get();
return(0);
}
float round(float n)
{
if ((n / 10) >= 0)
{
n--;
}
return(n);
}
Yah, I'm thinkin' someone's been puffin' the magic dragon.....
Err... I'm fairly sure the problem is that -- and ++ are not defined (by the standard) for floating point types. (Somebody please correct me if this is wrong.) If that is the case (as I suspect it is), then that explains why you two would be getting different results.
Quote:
Originally Posted by Zach L.
Seems to indicated that operator++ on floats and doubles is defined.Quote:
Originally Posted by CPP Standard 5.2.6.1
> I swear, it's working perfectly for me... 14.5 evaluates to 15, and 14.45 evaluates to 14.
Post an actual complete program which we can compile, which demonstrates the problem.
For all we know, you could be messing up the calling and/or the printing.
Also, state OS and compiler.
> that -- and ++ are not defined (by the standard) for floating point types.
I can't find anything to suggest that.
Thanks... I don't own a copy of the standard, and I had never seen anyone use those operators with float/double.
It does seem a bit odd, though, as ++ and -- are not always going to do anything to the value.
Cheers
I removed the function from the header file, and put it into the main source file, and it then worked as it should've....so something in the header file must've been messing things up..but I tried commenting all the functions out and it still worked weird. I suppose it's no big deal anymore though.
But anyhoo...I'm using Dev-C++ on Windows XP Home...and here's that header file that I was making for ........s and giggles.
Code:/*****************
Included files
*****************/
#include <iostream> //C++ input/output
#include <cstdlib> //Includes std functions
#include <math.h> //Math functions
using namespace std;
/************************************
Global Constants / Macros
************************************/
#define GREATER(x,y)(x>y?x:y) //Finds greater of two values
#define LESS(x,y)(x<y?x:y) //Finds lesser of two values
const double pi = 3.14159265; //Circumference:Diameter Ratio
const double e = 2.71828183; //Euler's Number
/************************************
Calculates factorial of a number (n!)
************************************/
int fact(int n){
int result=1;
//Special cases: n==0 and n<0
if(n==0){return 1;} //0! = 1
if(n<0) {return 0;} //Negative factorial is undefined
//If the number is positive:
while(n>0){
result *=n;
n--;
}
return result;
}
/**********************************
Calculates slope of a ramp or line
**********************************/
int Slope(int width, int height){
return height/width;
}
/***********************************
Calculates number raised to a power
***********************************/
double Pow(double base, double exp){
double result=1.00;
//If the exponent is greater than 0
if(exp>0){
for(int i=0;i<exp;i++)
result*=base;
}
//If the exponent is 0
if(exp==0){result=1;}
//If the exponent is less than 0
if(exp<0){
for(int i=0;i<exp;i++){
result*=base;
}
}
return result;
}
/****************************************************
The round function that I was working on until
I stumbled upon something that should not have worked,
but somehow did.
*****************************************************/
float round(float n){
if ((n / 10)>=0){
n--;}
return n;
}
round() is a C99 function in math.h ------ and it looks like it works too :)
gg
Here's an experiment (this is how I reproduced your problem)Quote:
Originally Posted by Krak
Make a new project. Put this in the main file of the project:
Don't make the header file part of the dev-c++ project.Code:#include "z.h" // or whatever your header file is named
int main()
{
float x;
int ix;
float y;
x = 14.45;
y = round(x);
ix = round(x);
cout << "x = " << x << ", y = " << y << ", ix = " << ix << endl;
x = 14.5;
y = round(x);
ix = round(x);
cout << "x = " << x << ", y = " << y << ", ix = " << ix << endl;
cin.get();
return 0;
}
Now take your original header file and change the round() function to this:
Note that this round() will not be compiled, because of the #if 0 .. #endifCode:/************************************************** **
The round function that I was working on until
I stumbled upon something that should not have worked,
but somehow did.
************************************************** ***/
#if 0
float round(float n){
cout << " in round(" << n << ")" << endl;
if ((n / 10)>=0){
n--;
}
return n;
}
#endif
Now press F9 (Execute->Compile & Run)
Here's what I got:
This is the correct result, based on round() in <cmath>Quote:
x = 14.45, y = 14
x = 14.5, y = 15
Now: delete the #if 0 and #endif around your float() in the header file. Don't change anything in main(). Execute compile-and-run again.
Here's what I got:
It is not executing your float(), since dev-cpp didn't actually recompile (since the header was not part of the project).Quote:
x = 14.45, y = 14
x = 14.5, y = 15
Now, in dev-c++, edit your main (add a space somewhere, or something). Do the compile-and-run thing again. Here's what I got:
As expected, now it's running your junky old round() function with the expected wrong answers.Quote:
in round(14.45)
x = 14.45, y = 13.45
in round(14.5)
x = 14.5, y = 13.5
To make sure this doesn't happen again, put add the header file to your dev-c++ project. Now comment out your round() again and compile-and-run. Now it works as expected (at least it does for me).
(I'm not saying that this is what happened, but it does reproduce the results you originally reported.)
Moral of the story: if you think it's doing something that it clearly shouldn't do, then put output statements in strategic places to see if it's really getting there.
An observation: using GUIs to compile projects can give unexpected results if you don't have the project set up correctly. (Same thing with command line compilation with make files.) Fortunately you were testing as you added new functions and recognized that the test results were inconsistent with sane behavior. Testing as you go is a Good Thing.
Of course, "most people" recommend that you not put executable code in header files in the first place, so "most people" would never see this behavior.
Anyhow, I think that it's important to chase down any anomalous behavior as you observe it. Sometimes compilers do have bugs. I don't think that's the case here.
Regards,
Dave
Or perhaps: don't create functions identical to the ones in the standard library while 'using namespace std'.Quote:
Moral of the story: if you think it's doing something that it clearly shouldn't do, then put output statements in strategic places to see if it's really getting there.
And I think it's particularly important that you not hide 'using namespace std' in header files.Quote:
Originally Posted by Sang-drax
The interesting thing is that I removed the 'using namespace std' and the '#include <math.h>' that the original poster had in the header file (added using std::cout, etc. to main).
"g++ -Wall -pedantic" gave no errors or warnings; it took the -ansi flag to actually give a warning. The program gave answers consistent with use of the standard round() function in <cmath>.
(But Borland and Microsoft compilers gave compiler errors using default warning settings).
Regards,
Dave
>It does seem a bit odd, though, as ++ and -- are not always going to do anything to the value.
Except add 1 or subtract 1 from the value. ;)
I *think* he was referring to type bool.
**EDIT**
I was under the impression too that ++ and -- weren't defined for floating-point types, but I just realized that I was confusing them with %. :rolleyes:
n++ and n-- basically being the same as:
n = n + 1.0f;
and
n = n - 1.0f;
unless they're part of a larger expression, in which case you have to worry about the pre and post increment/decrement rules.