errors when I make program concise!

toptony (39)
hello guys!

I has defined a class implement arbitrary precision arithmetic, to calculate the factorial of 1000.

This is the head file:
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class BigNumber{
    struct Nrep;
    Nrep* num;
public:
    BigNumber();
    BigNumber(char*);
    BigNumber(const BigNumber&);
    BigNumber(const int);
    BigNumber& operator=(char*);
    BigNumber& operator=(const BigNumber&);
    BigNumber& operator=(const int);
    ~BigNumber();
    BigNumber& operator+=(const BigNumber&);
    BigNumber& operator++(int);
    BigNumber& operator*=(const char);	
    BigNumber& operator*=(const BigNumber&);
    ...
}


and the main() funcition
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int _tmain(int argc, _TCHAR* argv[])
{
	BigNumber b0=1,b1 = 1;
	for(int i=0;i<num;i++)	{b1 *=b0;b0++;}
	...
}


and it works fine! and I get the factorial of 1000:
402387260077093773543702433923003985719374864210714632543799910429938512398629020592044208486969404800479988610197196058631666872994808558901323829669944590997424504087073759918823627727188732519779505950995276120874975462497043601418278094646496291056393887437886487337119181045825783647849977012476632889835955735432513185323958463075557409114262417474349347553428646576611667797396668820291207379143853719588249808126867838374559731746136085379534524221586593201928090878297308431392844403281231558611036976801357304216168747609675871348312025478589320767169132448426236131412508780208000261683151027341827977704784635868170164365024153691398281264810213092761244896359928705114964975419909342221566832572080821333186116811553615836546984046708975602900950537616475847728421889679646244945160765353408198901385442487984959953319101723355556602139450399736280750137837615307127761926849034352625200015888535147331611702103968175921510907788019393178114194545257223865541461062892187960223838971476088506276862967146674697562911234082439208160153780889893964518263243671616762179168909779911903754031274622289988005195444414282012187361745992642956581746628302955570299024324153181617210465832036786906117260158783520751516284225540265170483304226143974286933061690897968482590125458327168226458066526769958652682272807075781391858178889652208164348344825993266043367660176999612831860788386150279465955131156552036093988180612138558600301435694527224206344631797460594682573103790084024432438465657245014402821885252470935190620929023136493273497565513958720559654228749774011413346962715422845862377387538230483865688976461927383814900140767310446640259899490222221765904339901886018566526485061799702356193897017860040811889729918311021171229845901641921068884387121855646124960798722908519296819372388642614839657382291123125024186649353143970137428531926649875337218940694281434118520158014123344828015051399694290153483077644569099073152433278288269864602789864321139083506217095002597389863554277196742822248757586765752344220207573630569498825087968928162753848863396909959826280956121450994871701244516461260379029309120889086942028510640182154399457156805941872748998094254742173582401063677404595741785160829230135358081840096996372524230560855903700624271243416909004153690105933983835777939410970027753472000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
The number'sz is :2568 !

but when I want to make this program concise,like normal c++
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int _tmain(int argc, _TCHAR* argv[])
{
	BigNumber b0=1,b1 = 1;
	for(int i=0;i<num;i++)	b1 *=b0++;
	...
}

Then the result is not correct!
for example:
factorial of 4
it's result :120 correct is:24;
factorial of 10
it's result :39916800 correct is: 3628800;

:(
so anyone can help me to point out the errors of my implement: operator*=,operator++;
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BigNumber& BigNumber::operator*=(const BigNumber& b){	
	if ((b.size()==1)&&(b.read(0)=='0')) return *this=0;
	if((size()==1)&&(read(0)=='0')) return *this;
	if ((b.size()==1)&&(b.read(0)=='1')) return *this;
	if((size()==1)&&(read(0)=='1')) return *this=b;

	BigNumber t1(num->name) ;
	BigNumber t2=b;	
	int k=b.size();	
	char c1;
	for (int i=k;i>0;i--){
		c1=t2.read(i-1);
		if (i==k) 
			*this *= c1;
		else
			*this += t1 * c1;
		int j=t1.size();
		t1.insert(j,'0');
	}
	return *this;}

BigNumber& BigNumber::operator++(int){
	BigNumber b = "1";
	return *this+=b;}


thanks!
helios (17607)
You obviously have an off-by-one error, there.
120=5!, not 4!
39916800=11!, not 10!
toptony (39)
:)

thanks helios!

I know what you said about off-by-one error!

It will not have this error when you change the BigNum to int!
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.....
int i=1,j=1;
for (k=0 ;k<num;k++) i*=j++;
.......


it is what I want to understand!

thanks.
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