I don't understand why the following code always answers with 0.
#include <iostream>
using namespace std;
int main() {
int n,a,b;
cin>>n;
b=n%10;
while(n!=0) {
a=n%10;
n=n/10;
}
a=b;
b=a;
cout<<n<<endl;
return 0;
}
To swap two numbers, you need a temporary register
tmp=a;
a=b;
b=tmp;
However, if you are trying to swap digits in n, you need to change n. Which you have destroyed in your loop. Keep a copy of it beforehand?
Or simply note that floor(log(n)/log(10)) gives you the power of 10 for the first digit.
n=23456;
int firstdec = pow(10,floor(log(n)/log(10))); // eg 10000
int firstdig = n/firstdec; // eg 2
int lastdig = n%10; // eg 6
int removed = ((n-firstdig*firstdec)/10)*10 ; // eg 3450
int final = removed + lastdig*firstdec + firstdig; // eg 63452
This
a=b;
b=a;
looks nice.
Do you mean swap(a, b) or
int t = a;
a = b;
b = t;
?
And you're not actually changing n.
#include <iostream>
#include<math.h>
using namespace std;
int main()
{
int num, swno;
int fd, ld, digits;
// Reads a number from user
cout<<"Enter any number:";
cin>>num;
ld = num % 10; //Gets last digit
digits = (int)log10(num); //Total number of digits - 1
fd = (int)(num / pow(10, digits)); //Gets the first digit
swno = ld;
swno *= (int)pow(10, digits);
swno += num % ((int)pow(10, digits));
swno -= ld;
swno += fd;
cout<<"\nOriginal number = "<<num;
cout<<"\nNumber after swapping first and last digit: "<<swno;
return 0;
}
You code has some problems, like the variable swap. But also, you seem to expect that by changing a and b, n is changed accordingly, which is not going to happen.
First, because a and b are not references to the digits, they are mere copies. Second, you destroyed you n in the loop finding a, so even when you fix you swap the code will still print 0.
My recommendation is to convert the integer to a string, change the first and last, and then convert it back. It will be much simpler and more readable.
In order to do that you should take a look at stringstreams.
#include <iostream>
#include<string.h>
using namespace std;
int main(void){
int a;
char k,l;
cin>>a;
string s=to_string(a);
k=s[0];
l=s[s.length()-1];
s[0]=l;
s[s.length()-1]=k;
cout<<s;
return 0;
}
Here is what is missing in your code. real= entered value, first and last digits = firstd and lastd and i = number of digits of the entered number.
real -= lastd;
real += firstd;
real -= (firstd*i);
real += (lastd*i);
Related
#include<iostream>
#include<vector>
#include<cstdlib>
#include <cassert>
using namespace std;
long long int LastDigitofSumofFibonacci(int n){long long int first=0;
long long int second=1;
long long int fibOfn;
long long int sum=1;
vector<long long int> V;
V.push_back(first);
V.push_back(second);
if(n==0) return first;
else if(n==1) return second;
else{
for(int i=2;i<60;i++){
fibOfn=first+second;
first=second;
second=fibOfn;
sum=sum+fibOfn;
//cout<<"i "<<i<<" fibOfn "<<fibOfn<<" fibOfnlastdigit "<<fibOfnlastdigit<<" first "<<first<<" second "<<second<<" sum "<<sum;
//cout<<endl;
sum=sum%10;
V.push_back(sum);
}
}
//for(auto element:V)
//cout<<element<<" ";
//cout<<endl;
//cout<<(n)%60<<endl;
return V[(n)%60];
}
int main(){
int n;
cin>>n;
long long int Base=LastDigitofSumofFibonacci(n);
cout<<Base<<endl;
}
In this I am trying to calculate the the last digit of Fibonacci series. I know and also read from net that last digit follow pattern of 60(0-59). from that concept wise I think my code is OK. but still I am unable to get the correct answers for large digit number.
I cleaned up the code a bit and fixed the issue with second not being computed % 10.
Since only the last digit is relevant all variables can be just int, no need for long long int to store a single digit. It would actually save ram to use uint8_t as type for the cache, but 60 bytes or 240 bytes isn't going to make a difference here.
The result repeats every 60 steps, which is the basis for the algorithm. But why compute this every time the function gets called? So lets make a static array so the computation only happens once. Lets go one step further with constinit and compute it at compile time.
As last change I made the argument to LastDigitofSumofFibonacci unsigned int. Unless you want to extend the fibonacci series backwards into the negative and extend the algorithm. unsigned int generates better code for n % 60.
#include <iostream>
#include <array>
int LastDigitofSumofFibonacci(unsigned int n) {
// The last digit of `fib(n)` and their sum repeats every 60 steps.
// https://en.wikipedia.org/wiki/Pisano_period
// Compute the first 60 values as lookup table at compile time.
static constinit std::array<int, 60> cache = []() {
int first = 0, second = 1;
std::array<int, 60> a{0, 1};
for (int i = 2; i < 60; i++) {
int t = first + second;
first = second;
second = t % 10;
a[i] = (a[i - 1] + t) % 10;
}
return a;
}();
// and now just look up the answer at run time.
return cache[n % 60];
}
int main(){
int n;
std::cin >> n;
std::cout << LastDigitofSumofFibonacci(n) << std::endl;
}
Somehow the code got a lot shorter just from eliminating some overhead here and there.
I have to code a program in which a user input some number and the program have to swap the first digit form last number.
For Example user inputs: 12345
The expected output would then be: 52341
But I am getting an error and getting output like: 4465
This is my Code:
#include <iostream>
#include <cmath>
using namespace std;
void main()
{ int num,ln,fn,pw,dg,swap;
cin >> num;
ln = num%10 ;
dg = log10(num);
pw = pow(10,dg);
fn = num%pw;
swap = ln*pw;
swap = swap+num/pw;
swap = swap-ln;
swap = swap+fn;
cout << swap << endl;
system ("pause");
}
Help me to solve this.
Ok I'll do it.
0. Design choice(s)
The operation you want to do is not on the value of the input number but rather on its representation, specifically in base 10. We'd better go for a string manipulation then.
1. Integer to string
With C++11 and following, we do have std::to_string: takes an integer, returns a string, done.
2. Accessing characters from a string
If the string is not empty, std::string::front() and std::string::back() return a reference to the first and last characters of that string, easy.
3. Swapping characters
We have the utility std::swap and the swap idiom
using std::swap;
swap(lhs, rhs);
lhs and rhs being what needs to be swapped (see step 2.).
4. Back to integer
We have std::stoi doing what std::to_string does but in reverse, done. But what if the new integer has become too big to be held by an integer type?
5. Putting all together
Let's define a (free) function!
int reverse_border_digits(int value)
{
// steps 1 through 4
return result;
}
Here's an answer fulfilling the OP requirements
#include <iostream>
#include <cmath>
using namespace std;
int main()
{
int num;
cin >> num;
int dg = (int)(log10(num + 0.000001)); // add small delta to avoid any possible rounding error on an exact power of ten
int pw = (int)round(pow(10.0, dg));
int swap = (num % 10) * pw + (num - num % 10 - (num / pw) * pw) + num / pw;
cout << swap << '\n';
}
the point of this exercise is to multiply a digit of a number with its current position and then add it with the others. Example: 1234 = 1x4 + 2x3 + 3x2 + 4x1 .I did this code successfully using 2 parameters and now i'm trying to do it with 1. My idea was to use - return num + mult(a/10) * (a%10) and get the answer, , because from return num + mult(a/10) i get the values 1,2,3,4- (1 is for mult(1), 2 for mult(12), etc.) for num, but i noticed that this is only correct for mult(1) and then the recursion gets wrong values for mult(12), mult(123), mult(1234). My idea is to independently multiply the values from 'num' with a%10 . Sorry if i can't explain myself that well, but i'm still really new to programming.
#include <iostream>
using namespace std;
int mult(int a){
int num = 1;
if (a==0){
return 1;
}
return ((num + mult(a/10)) * (a%10));
}
int main()
{
int a = 1234;
cout << mult(a);
return 0;
}
I find this easier and more logically to do, Hope this helps lad.
int k=1;
int a=1234;
int sum=0;
while(a>0){
sum=sum+k*(a%10);
a=a/10;
k++;
}
If the goal is to do it with recursion and only one argument, you may achieve it with two functions. This is not optimal in terms of number of operations performed, though. Also, it's more of a math exercise than a programming one:
#include <iostream>
using namespace std;
int mult1(int a) {
if(a == 0) return 0;
return a % 10 + mult1(a / 10);
}
int mult(int a) {
if(a == 0) return 0;
return mult1(a) + mult(a / 10);
}
int main() {
int a = 1234;
cout << mult(a) << '\n';
return 0;
}
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;
}
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.