Related
So..
Here is the code:
#include <iostream>
#include <limits>
#include <math.h>
using namespace std;
int main()
{
unsigned long long i,y,n,x=45;
unsigned long long factorial = 1;
for(n = 0; n <= 5; n++)
{
y = (pow(-1,n)*pow(x,2*n)) / factorial;
cout << "COS IS " << y << endl;
}
for(int i = 1; i <=n; i++)
{
factorial *= 2*i;
}
}
I get an overflow but I really don't know why. I use unsigned long long just to make sure that I on't get but.. I still get it. Even limited to small numbers. I tried to implement this:
https://en.wikibooks.org/wiki/Trigonometry/Power_Series_for_Cosine_and_Sine
But I really can't do it because of the overflow. Do you have any ideea on what can I do ? I am newbie in programming so, take it easy on me :D
There are many issues.
you use integer types when you should use floating point types
you use unsigned types for signed calculations
you don't use radians but degrees (45° ≈ 0.78539 radians)
you don't calculate the factorial in the loop, it is always 1, you only calculate it at the end of the loop but then it's too late, and your calculation of the factorial is wrong anyway.
the algorithm is wrong, it just doesn't do what Maclaurin's therorem says, you need to sum up the terms, but you just print the terms.
You probably want this:
#include <iostream>
#include <cmath>
using namespace std;
long factorial(int n)
{
long result = 1;
for (int i = 1; i <= n; i++)
result *= i;
return result;
}
int main()
{
double x = 0.785398163397448309616; //PI/4 expectd result COS(PI/4) = 0.7071067
double mycosinus = 0;
for (int n = 0; n <= 5; n++)
{
mycosinus += (pow(-1, n) * pow(x, 2 * n)) / factorial(2*n);
cout << "COS IS " << mycosinus << endl;
}
}
This is your wrong algorithm for calculating the factorial of 5:
int main()
{
int n = 5;
int factorial = 1;
for (int i = 1; i <= n; i++)
{
factorial *= 2 * i;
}
cout << "factorial 5 = " << factorial << endl;
}
The calculated value is 3840 instead of 120. I let you find out what's wrong yourself.
For performing this sort of maths you need to use a floating point like float or double not integral types like long, int or long long, given that sin and cos can both return negative numbers you shouldn't be using unsigned either.
I'm trying to find a way to find the length of an integer (number of digits) and then place it in an integer array. The assignment also calls for doing this without the use of classes from the STL, although the program spec does say we can use "common C libraries" (gonna ask my professor if I can use cmath, because I'm assuming log10(num) + 1 is the easiest way, but I was wondering if there was another way).
Ah, and this doesn't have to handle negative numbers. Solely non-negative numbers.
I'm attempting to create a variant "MyInt" class that can handle a wider range of values using a dynamic array. Any tips would be appreciated! Thanks!
Not necessarily the most efficient, but one of the shortest and most readable using C++:
std::to_string(num).length()
The number of digits of an integer n in any base is trivially obtained by dividing until you're done:
unsigned int number_of_digits = 0;
do {
++number_of_digits;
n /= base;
} while (n);
There is a much better way to do it
#include<cmath>
...
int size = trunc(log10(num)) + 1
....
works for int and decimal
If you can use C libraries then one method would be to use sprintf, e.g.
#include <cstdio>
char s[32];
int len = sprintf(s, "%d", i);
"I mean the number of digits in an integer, i.e. "123" has a length of 3"
int i = 123;
// the "length" of 0 is 1:
int len = 1;
// and for numbers greater than 0:
if (i > 0) {
// we count how many times it can be divided by 10:
// (how many times we can cut off the last digit until we end up with 0)
for (len = 0; i > 0; len++) {
i = i / 10;
}
}
// and that's our "length":
std::cout << len;
outputs 3
Closed formula for the longest int (I used int here, but works for any signed integral type):
1 + (int) ceil((8*sizeof(int)-1) * log10(2))
Explanation:
sizeof(int) // number bytes in int
8*sizeof(int) // number of binary digits (bits)
8*sizeof(int)-1 // discount one bit for the negatives
(8*sizeof(int)-1) * log10(2) // convert to decimal, because:
// 1 bit == log10(2) decimal digits
(int) ceil((8*sizeof(int)-1) * log10(2)) // round up to whole digits
1 + (int) ceil((8*sizeof(int)-1) * log10(2)) // make room for the minus sign
For an int type of 4 bytes, the result is 11. An example of 4 bytes int with 11 decimal digits is: "-2147483648".
If you want the number of decimal digits of some int value, you can use the following function:
unsigned base10_size(int value)
{
if(value == 0) {
return 1u;
}
unsigned ret;
double dval;
if(value > 0) {
ret = 0;
dval = value;
} else {
// Make room for the minus sign, and proceed as if positive.
ret = 1;
dval = -double(value);
}
ret += ceil(log10(dval+1.0));
return ret;
}
I tested this function for the whole range of int in g++ 9.3.0 for x86-64.
int intLength(int i) {
int l=0;
for(;i;i/=10) l++;
return l==0 ? 1 : l;
}
Here's a tiny efficient one
Being a computer nerd and not a maths nerd I'd do:
char buffer[64];
int len = sprintf(buffer, "%d", theNum);
Would this be an efficient approach? Converting to a string and finding the length property?
int num = 123
string strNum = to_string(num); // 123 becomes "123"
int length = strNum.length(); // length = 3
char array[3]; // or whatever you want to do with the length
How about (works also for 0 and negatives):
int digits( int x ) {
return ( (bool) x * (int) log10( abs( x ) ) + 1 );
}
Best way is to find using log, it works always
int len = ceil(log10(num))+1;
Code for finding Length of int and decimal number:
#include<iostream>
#include<cmath>
using namespace std;
int main()
{
int len,num;
cin >> num;
len = log10(num) + 1;
cout << len << endl;
return 0;
}
//sample input output
/*45566
5
Process returned 0 (0x0) execution time : 3.292 s
Press any key to continue.
*/
There are no inbuilt functions in C/C++ nor in STL for finding length of integer but there are few ways by which it can found
Here is a sample C++ code to find the length of an integer, it can be written in a function for reuse.
#include<iostream>
using namespace std;
int main()
{
long long int n;
cin>>n;
unsigned long int integer_length = 0;
while(n>0)
{
integer_length++;
n = n/10;
}
cout<<integer_length<<endl;
return 0;
}
Here is another way, convert the integer to string and find the length, it accomplishes same with a single line:
#include<iostream>
#include<cstring>
using namespace std;
int main()
{
long long int n;
cin>>n;
unsigned long int integer_length = 0;
// convert to string
integer_length = to_string(n).length();
cout<<integer_length<<endl;
return 0;
}
Note: Do include the cstring header file
The easiest way to use without any libraries in c++ is
#include <iostream>
using namespace std;
int main()
{
int num, length = 0;
cin >> num;
while(num){
num /= 10;
length++;
}
cout << length;
}
You can also use this function:
int countlength(int number)
{
static int count = 0;
if (number > 0)
{
count++;
number /= 10;
countlength(number);
}
return count;
}
#include <math.h>
int intLen(int num)
{
if (num == 0 || num == 1)
return 1;
else if(num < 0)
return ceil(log10(num * -1))+1;
else
return ceil(log10(num));
}
Most efficient code to find length of a number.. counts zeros as well, note "n" is the number to be given.
#include <iostream>
using namespace std;
int main()
{
int n,len= 0;
cin>>n;
while(n!=0)
{
len++;
n=n/10;
}
cout<<len<<endl;
return 0;
}
Is it possible to take an array filled with 2 digit numbers e.g.
[10,11,12,13,...]
and multiply each element in the list by 100^(position in the array) and sum the result so that:
mysteryFunction[10,11,12] //The function performs 10*100^0 + 11*100^1 + 12*100^3
= 121110
and also
mysteryFunction[10,11,12,13]
= 13121110
when I do not know the number of elements in the array?
(yes, the reverse of order is intended but not 100% necessary, and just in case you missed it the first time the numbers will always be 2 digits)
Just for a bit of background to the problem: this is to try to improve my attempt at an RSA encryption program, at the moment I am multiplying each member of the array by 100^(the position of the number) written out each time which means that each word which I use to encrypt must be a certain length.
For example to encrypt "ab" I have converted it to an array [10,11] but need to convert it to 1110 before I can put it through the RSA algorithm. I would need to adjust my code for if I then wanted to use a three letter word, again for a four letter word etc. which I'm sure you will agree is not ideal. My code is nothing like industry standard but I am happy to upload it should anyone want to see it (I have also already managed this in Haskell if anyone would like to see that). I thought that the background information was necessary just so that I don't get hundreds of downvotes from people thinking that I'm trying to trick them into doing homework for me. Thank you very much for any help, I really do appreciate it!
EDIT: Thank you for all of the answers! They perfectly answer the question that I asked but I am having problems incorporating them into my current program, if I post my code so far would you be able to help? When I tried to include the answer provided I got an error message (I can't vote up because I don't have enough reputation, sorry that I haven't accepted any answers yet).
#include <iostream>
#include <string>
#include <math.h>
int returnVal (char x)
{
return (int) x;
}
unsigned long long modExp(unsigned long long b, unsigned long long e, unsigned long long m)
{
unsigned long long remainder;
int x = 1;
while (e != 0)
{
remainder = e % 2;
e= e/2;
if (remainder == 1)
x = (x * b) % m;
b= (b * b) % m;
}
return x;
}
int main()
{
unsigned long long p = 80001;
unsigned long long q = 70021;
int e = 7;
unsigned long long n = p * q;
std::string foo = "ab";
for (int i = 0; i < foo.length(); i++);
{
std::cout << modExp (returnVal((foo[0]) - 87) + returnVal (foo[1] -87) * 100, e, n);
}
}
If you want to use plain C-style arrays, you will have to separately know the number of entries. With this approach, your mysterious function might be defined like this:
unsigned mysteryFunction(unsigned numbers[], size_t n)
{
unsigned result = 0;
unsigned factor = 1;
for (size_t i = 0; i < n; ++i)
{
result += factor * numbers[i];
factor *= 100;
}
return result;
}
You can test this code with the following:
#include <iostream>
int main()
{
unsigned ar[] = {10, 11, 12, 13};
std::cout << mysteryFunction(ar, 4) << "\n";
return 0;
}
On the other hand, if you want to utilize the STL's vector class, you won't separately need the size. The code itself won't need too many changes.
Also note that the built-in integer types cannot handle very large numbers, so you might want to look into an arbitrary precision number library, like GMP.
EDIT: Here's a version of the function which accepts a std::string and uses the characters' ASCII values minus 87 as the numbers:
unsigned mysteryFunction(const std::string& input)
{
unsigned result = 0;
unsigned factor = 1;
for (size_t i = 0; i < input.size(); ++i)
{
result += factor * (input[i] - 87);
factor *= 100;
}
return result;
}
The test code becomes:
#include <iostream>
#include <string>
int main()
{
std::string myString = "abcde";
std::cout << mysteryFunction(myString) << "\n";
return 0;
}
The program prints: 1413121110
As benedek mentioned, here's an implementation using dynamic arrays via std::vector.
unsigned mystery(std::vector<unsigned> vect)
{
unsigned result = 0;
unsigned factor = 1;
for (auto& item : vect)
{
result += factor * item;
factor *= 100;
}
return result;
}
void main(void)
{
std::vector<unsigned> ar;
ar.push_back(10);
ar.push_back(11);
ar.push_back(12);
ar.push_back(13);
std::cout << mystery(ar);
}
I would like to suggest the following solutions.
You could use standard algorithm std::accumulate declared in header <numeric>
For example
#include <iostream>
#include <numeric>
int main()
{
unsigned int a[] = { 10, 11, 12, 13 };
unsigned long long i = 1;
unsigned long long s =
std::accumulate( std::begin( a ), std::end( a ), 0ull,
[&]( unsigned long long acc, unsigned int x )
{
return ( acc += x * i, i *= 100, acc );
} );
std::cout << "s = " << s << std::endl;
return 0;
}
The output is
s = 13121110
The same can be done with using the range based for statement
#include <iostream>
#include <numeric>
int main()
{
unsigned int a[] = { 10, 11, 12, 13 };
unsigned long long i = 1;
unsigned long long s = 0;
for ( unsigned int x : a )
{
s += x * i; i *= 100;
}
std::cout << "s = " << s << std::endl;
return 0;
}
You could also write a separate function
unsigned long long mysteryFunction( const unsigned int a[], size_t n )
{
unsigned long long s = 0;
unsigned long long i = 1;
for ( size_t k = 0; k < n; k++ )
{
s += a[k] * i; i *= 100;
}
return s;
}
Also think about using std::string instead of integral numbers to keep an encrypted result.
I am doing a factorial program with strings because i need the factorial of Numbers greater than 250
I intent with:
string factorial(int n){
string fact="1";
for(int i=2; i<=n; i++){
b=atoi(fact)*n;
}
}
But the problem is that atoi not works. How can i convert my string in a integer.
And The most important Do I want to know if the program of this way will work with the factorial of 400 for example?
Not sure why you are trying to use string. Probably to save some space by not using integer vector? This is my solution by using integer vector to store factorial and print.Works well with 400 or any large number for that matter!
//Factorial of a big number
#include<iostream>
#include<vector>
using namespace std;
int main(){
int num;
cout<<"Enter the number :";
cin>>num;
vector<int> res;
res.push_back(1);
int carry=0;
for(int i=2;i<=num;i++){
for(int j=0;j<res.size();j++){
int tmp=res[j]*i;
res[j]=(tmp+carry)%10 ;
carry=(tmp+carry)/10;
}
while(carry!=0){
res.push_back(carry%10);
carry=carry/10;
}
}
for(int i=res.size()-1;i>=0;i--) cout<<res[i];
cout<<endl;
return 0;
}
Enter the number :400
Factorial of 400 :64034522846623895262347970319503005850702583026002959458684445942802397169186831436278478647463264676294350575035856810848298162883517435228961988646802997937341654150838162426461942352307046244325015114448670890662773914918117331955996440709549671345290477020322434911210797593280795101545372667251627877890009349763765710326350331533965349868386831339352024373788157786791506311858702618270169819740062983025308591298346162272304558339520759611505302236086810433297255194852674432232438669948422404232599805551610635942376961399231917134063858996537970147827206606320217379472010321356624613809077942304597360699567595836096158715129913822286578579549361617654480453222007825818400848436415591229454275384803558374518022675900061399560145595206127211192918105032491008000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
There's a web site that will calculate factorials for you: http://www.nitrxgen.net/factorialcalc.php. It reports:
The resulting factorial of 250! is 493 digits long.
The result also contains 62 trailing zeroes (which constitutes to 12.58% of the whole number)
3232856260909107732320814552024368470994843717673780666747942427112823747555111209488817915371028199450928507353189432926730931712808990822791030279071281921676527240189264733218041186261006832925365133678939089569935713530175040513178760077247933065402339006164825552248819436572586057399222641254832982204849137721776650641276858807153128978777672951913990844377478702589172973255150283241787320658188482062478582659808848825548800000000000000000000000000000000000000000000000000000000000000
Many systems using C++ double only work up to 1E+308 or thereabouts; the value of 250! is too large to store in such numbers.
Consequently, you'll need to use some sort of multi-precision arithmetic library, either of your own devising using C++ string values, or using some other widely-used multi-precision library (GNU GMP for example).
The code below uses unsigned double long to calculate very large digits.
#include<iostream.h>
int main()
{
long k=1;
while(k!=0)
{
cout<<"\nLarge Factorial Calculator\n\n";
cout<<"Enter a number be calculated:";
cin>>k;
if (k<=33)
{
unsigned double long fact=1;
fact=1;
for(int b=k;b>=1;b--)
{
fact=fact*b;
}
cout<<"\nThe factorial of "<<k<<" is "<<fact<<"\n";
}
else
{
int numArr[10000];
int total,rem=0,count;
register int i;
//int i;
for(i=0;i<10000;i++)
numArr[i]=0;
numArr[10000]=1;
for(count=2;count<=k;count++)
{
while(i>0)
{
total=numArr[i]*count+rem;
rem=0;
if(total>9)
{
numArr[i]=total%10;
rem=total/10;
}
else
{
numArr[i]=total;
}
i--;
}
rem=0;
total=0;
i=10000;
}
cout<<"The factorial of "<<k<<" is \n\n";
for(i=0;i<10000;i++)
{
if(numArr[i]!=0 || count==1)
{
cout<<numArr[i];
count=1;
}
}
cout<<endl;
}
cout<<"\n\n";
}//while
return 0;
}
Output:
![Large Factorial Calculator
Enter a number be calculated:250
The factorial of 250 is
32328562609091077323208145520243684709948437176737806667479424271128237475551112
09488817915371028199450928507353189432926730931712808990822791030279071281921676
52724018926473321804118626100683292536513367893908956993571353017504051317876007
72479330654023390061648255522488194365725860573992226412548329822048491377217766
50641276858807153128978777672951913990844377478702589172973255150283241787320658
18848206247858265980884882554880000000000000000000000000000000000000000000000000
000000000000][1]
You can make atoi compile by adding c_str(), but it will be a long way to go till getting factorial. Currently you have no b around. And if you had, you still multiply int by int. So even if you eventually convert that to string before return, your range is still limited. Until you start to actually do multiplication with ASCII or use a bignum library there's no point to have string around.
Your factorial depends on conversion to int, which will overflow pretty fast, so you want be able to compute large factorials that way. To properly implement computation on big numbers you need to implement logic as for computation on paper, rules that you were tought in primary school, but treat long long ints as "atoms", not individual digits. And don't do it on strings, it would be painfully slow and full of nasty conversions
If you are going to solve factorial for numbers larger than around 12, you need a different approach than using atoi, since that just gives you a 32-bit integer, and no matter what you do, you are not going to get more than 2 billion (give or take) out of that. Even if you double the size of the number, you'll only get to about 20 or 21.
It's not that hard (relatively speaking) to write a string multiplication routine that takes a small(ish) number and multiplies each digit and ripples the results through to the the number (start from the back of the number, and fill it up).
Here's my obfuscated code - it is intentionally written such that you can't just take it and hand in as school homework, but it appears to work (matches the number in Jonathan Leffler's answer), and works up to (at least) 20000! [subject to enough memory].
std::string operator*(const std::string &s, int x)
{
int l = (int)s.length();
std::string r;
r.resize(l);
std::fill(r.begin(), r.end(), '0');
int b = 0;
int e = ~b;
const int c = 10;
for(int i = l+e; i != e;)
{
int d = (s[i]-0x30) * x, p = i + b;
while (d && p > e)
{
int t = r[p] - 0x30 + (d % c);
r[p] = (t % c) + 0x30;
d = t / c + d / c;
p--;
}
while (d)
{
r = static_cast<char>((d % c) +0x30)+r;
d /= c;
b++;
}
i--;
}
return r;
}
In C++, the largest integer type is 'long long', and it hold 64 bits of memory, so obviously you can't store 250! in an integer type. It is a clever idea to use strings, but what you are basically doing with your code is (I have never used the atoi() function, so I don't know if it even works with strings larger than 1 character, but it doesn't matter):
covert the string to integer (a string that if this code worked well, in one moment contains the value of 249!)
multiply the value of the string
So, after you are done multiplying, you don't even convert the integer back to string. And even if you did that, at one moment when you convert the string back to an integer, your program will crash, because the integer won't be able to hold the value of the string.
My suggestion is, to use some class for big integers. Unfortunately, there isn't one available in C++, so you'll have to code it by yourself or find one on the internet. But, don't worry, even if you code it by yourself, if you think a little, you'll see it's not that hard. You can even use your idea with the strings, which, even tough is not the best approach, for this problem, will still yield the results in the desired time not using too much memory.
This is a typical high precision problem.
You can use an array of unsigned long long instead of string.
like this:
struct node
{
unsigned long long digit[100000];
}
It should be faster than string.
But You still can use string unless you are urgent.
It may take you a few days to calculate 10000!.
I like use string because it is easy to write.
#include <bits/stdc++.h>
#pragma GCC optimize (2)
using namespace std;
const int MAXN = 90;
int n, m;
int a[MAXN];
string base[MAXN], f[MAXN][MAXN];
string sum, ans;
template <typename _T>
void Swap(_T &a, _T &b)
{
_T temp;
temp = a;
a = b;
b = temp;
}
string operator + (string s1, string s2)
{
string ret;
int digit, up = 0;
int len1 = s1.length(), len2 = s2.length();
if (len1 < len2) Swap(s1, s2), Swap(len1, len2);
while(len2 < len1) s2 = '0' + s2, len2++;
for (int i = len1 - 1; i >= 0; i--)
{
digit = s1[i] + s2[i] - '0' - '0' + up; up = 0;
if (digit >= 10) up = digit / 10, digit %= 10;
ret = char(digit + '0') + ret;
}
if (up) ret = char(up + '0') + ret;
return ret;
}
string operator * (string str, int p)
{
string ret = "0", f; int digit, mul;
int len = str.length();
for (int i = len - 1; i >= 0; i--)
{
f = "";
digit = str[i] - '0';
mul = p * digit;
while(mul)
{
digit = mul % 10 , mul /= 10;
f = char(digit + '0') + f;
}
for (int j = 1; j < len - i; j++) f = f + '0';
ret = ret + f;
}
return ret;
}
int main()
{
freopen("factorial.out", "w", stdout);
string ans = "1";
for (int i = 1; i <= 5000; i++)
{
ans = ans * i;
cout << i << "! = " << ans << endl;
}
return 0;
}
Actually, I know where the problem raised At the point where we multiply , there is the actual problem ,when numbers get multiplied and get bigger and bigger.
this code is tested and is giving the correct result.
#include <bits/stdc++.h>
using namespace std;
#define mod 72057594037927936 // 2^56 (17 digits)
// #define mod 18446744073709551616 // 2^64 (20 digits) Not supported
long long int prod_uint64(long long int x, long long int y)
{
return x * y % mod;
}
int main()
{
long long int n=14, s = 1;
while (n != 1)
{
s = prod_uint64(s , n) ;
n--;
}
}
Expexted output for 14! = 87178291200
The logic should be:
unsigned int factorial(int n)
{
unsigned int b=1;
for(int i=2; i<=n; i++){
b=b*n;
}
return b;
}
However b may get overflowed. So you may use a bigger integral type.
Or you can use float type which is inaccurate but can hold much bigger numbers.
But it seems none of the built-in types are big enough.
I am trying to solve a problem, a part of which requires me to calculate (2^n)%1000000007 , where n<=10^9. But my following code gives me output "0" even for input like n=99.
Is there anyway other than having a loop which multilplies the output by 2 every time and finding the modulo every time (this is not I am looking for as this will be very slow for large numbers).
#include<stdio.h>
#include<math.h>
#include<iostream>
using namespace std;
int main()
{
unsigned long long gaps,total;
while(1)
{
cin>>gaps;
total=(unsigned long long)powf(2,gaps)%1000000007;
cout<<total<<endl;
}
}
You need a "big num" library, it is not clear what platform you are on, but start here:
http://gmplib.org/
this is not I am looking for as this will be very slow for large numbers
Using a bigint library will be considerably slower pretty much any other solution.
Don't take the modulo every pass through the loop: rather, only take it when the output grows bigger than the modulus, as follows:
#include <iostream>
int main() {
int modulus = 1000000007;
int n = 88888888;
long res = 1;
for(long i=0; i < n; ++i) {
res *= 2;
if(res > modulus)
res %= modulus;
}
std::cout << res << std::endl;
}
This is actually pretty quick:
$ time ./t
./t 1.19s user 0.00s system 99% cpu 1.197 total
I should mention that the reason this works is that if a and b are equivalent mod m (that is, a % m = b % m), then this equality holds multiple k of a and b (that is, the foregoing equality implies (a*k)%m = (b*k)%m).
Chris proposed GMP, but if you need just that and want to do things The C++ Way, not The C Way, and without unnecessary complexity, you may just want to check this out - it generates few warnings when compiling, but is quite simple and Just Works™.
You can split your 2^n into chunks of 2^m. You need to find: `
2^m * 2^m * ... 2^(less than m)
Number m should be 31 is for 32-bit CPU. Then your answer is:
chunk1 % k * chunk2 * k ... where k=1000000007
You are still O(N). But then you can utilize the fact that all chunk % k are equal except last one and you can make it O(1)
I wrote this function. It is very inefficient but it works with very large numbers. It uses my self-made algorithm to store big numbers in arrays using a decimal like system.
mpfr2.cpp
#include "mpfr2.h"
void mpfr2::mpfr::setNumber(std::string a) {
for (int i = a.length() - 1, j = 0; i >= 0; ++j, --i) {
_a[j] = a[i] - '0';
}
res_size = a.length();
}
int mpfr2::mpfr::multiply(mpfr& a, mpfr b)
{
mpfr ans = mpfr();
// One by one multiply n with individual digits of res[]
int i = 0;
for (i = 0; i < b.res_size; ++i)
{
for (int j = 0; j < a.res_size; ++j) {
ans._a[i + j] += b._a[i] * a._a[j];
}
}
for (i = 0; i < a.res_size + b.res_size; i++)
{
int tmp = ans._a[i] / 10;
ans._a[i] = ans._a[i] % 10;
ans._a[i + 1] = ans._a[i + 1] + tmp;
}
for (i = a.res_size + b.res_size; i >= 0; i--)
{
if (ans._a[i] > 0) break;
}
ans.res_size = i+1;
a = ans;
return a.res_size;
}
mpfr2::mpfr mpfr2::mpfr::pow(mpfr a, mpfr b) {
mpfr t = a;
std::string bStr = "";
for (int i = b.res_size - 1; i >= 0; --i) {
bStr += std::to_string(b._a[i]);
}
int i = 1;
while (!0) {
if (bStr == std::to_string(i)) break;
a.res_size = multiply(a, t);
// Debugging
std::cout << "\npow() iteration " << i << std::endl;
++i;
}
return a;
}
mpfr2.h
#pragma once
//#infdef MPFR2_H
//#define MPFR2_H
// C standard includes
#include <iostream>
#include <string>
#define MAX 0x7fffffff/32/4 // 2147483647
namespace mpfr2 {
class mpfr
{
public:
int _a[MAX];
int res_size;
void setNumber(std::string);
static int multiply(mpfr&, mpfr);
static mpfr pow(mpfr, mpfr);
};
}
//#endif
main.cpp
#include <iostream>
#include <fstream>
// Local headers
#include "mpfr2.h" // Defines local mpfr algorithm library
// Namespaces
namespace m = mpfr2; // Reduce the typing a bit later...
m::mpfr tetration(m::mpfr, int);
int main() {
// Hardcoded tests
int x = 7;
std::ofstream f("out.txt");
m::mpfr t;
for(int b=1; b<x;b++) {
std::cout << "2^^" << b << std::endl; // Hardcoded message
t.setNumber("2");
m::mpfr res = tetration(t, b);
for (int i = res.res_size - 1; i >= 0; i--) {
std::cout << res._a[i];
f << res._a[i];
}
f << std::endl << std::endl;
std::cout << std::endl << std::endl;
}
char c; std::cin.ignore(); std::cin >> c;
return 0;
}
m::mpfr tetration(m::mpfr a, int b)
{
m::mpfr tmp = a;
if (b <= 0) return m::mpfr();
for (; b > 1; b--) tmp = m::mpfr::pow(a, tmp);
return tmp;
}
I created this for tetration and eventually hyperoperations. When the numbers get really big it can take ages to calculate and a lot of memory. The #define MAX 0x7fffffff/32/4 is the number of decimals one number can have. I might make another algorithm later to combine multiple of these arrays into one number. On my system the max array length is 0x7fffffff aka 2147486347 aka 2^31-1 aka int32_max (which is usually the standard int size) so I had to divide int32_max by 32 to make the creation of this array possible. I also divided it by 4 to reduce memory usage in the multiply() function.
- Jubiman