I wrote program to convert decimal to binary for practice purposes but i get some strange output. When doing modulo with decimal number, i get correct value but what goes in array is forward slash? I am using char array for being able to just use output with cout <<.
// web binary converter: http://mistupid.com/computers/binaryconv.htm
#include <iostream>
#include <math.h>
#include <malloc.h> // _msize
#include <climits>
#define WRITEL(x) cout << x << endl;
#define WRITE(x) cout << x;
using std::cout;
using std::endl;
using std::cin;
char * decimalToBinary(int decimal);
void decimal_to_binary_char_array();
static char * array_main;
char * decimalToBinary(int decimal) // tied to array_main
{
WRITEL("Number to convert: " << decimal << "\n");
char * binary_array;
int t = decimal, // for number of digits
digits = 0, // number of digits
bit_count = 0; // total digit number of binary number
static unsigned int array_size = 0;
if(decimal < 0) { t = decimal; t = -t; } // if number is negative, make it positive
while(t > 0) { t /= 10; digits++; } // determine number of digits
array_size = (digits * sizeof(int) * 3); // number of bytes to allocate to array_main
WRITEL("array_size in bytes: " << array_size);
array_main = new char[array_size];
int i = 0; // counter for number of binary digits
while(decimal > 0)
{
array_main[i] = (char) decimal % 2 + '0';
WRITE("decimal % 2 = " << char (decimal % 2 + '0') << " ");
WRITE(array_main[i] << " ");
decimal = decimal / 2;
WRITEL(decimal);
i++;
}
bit_count = i;
array_size = bit_count * sizeof(int) + 1;
binary_array = new char[bit_count * sizeof(int)];
for(int i=0; i<bit_count+1; i++)
binary_array[i] = array_main[bit_count-1-i];
//array_main[bit_count * sizeof(int)] = '\0';
//WRITEL("\nwhole binary_array: "); for(int i=0; i<array_size; i++) WRITE(binary_array[i]); WRITEL("\n");
delete [] array_main;
return binary_array;
}
int main(void)
{
int num1 = 3001;
// 3001 = 101110111001
// 300 = 100101100
// 1000 = 1111101000
// 1200 = 10010110000
// 1000000 = 11110100001001000000
// 200000 = 110000110101000000
array_main = decimalToBinary(num1);
WRITEL("\nMAIN: " << array_main);
cin.get();
delete [] array_main;
return 0;
}
The output:
Number to convert: 3001
array_size in bytes: 48
decimal % 2 = 1 / 1500
decimal % 2 = 0 0 750
decimal % 2 = 0 0 375
decimal % 2 = 1 1 187
decimal % 2 = 1 / 93
decimal % 2 = 1 1 46
decimal % 2 = 0 0 23
decimal % 2 = 1 1 11
decimal % 2 = 1 1 5
decimal % 2 = 1 1 2
decimal % 2 = 0 1 1
decimal % 2 = 1 1 0
MAIN: 1111101/100/
What are those forward slashes in output (1111101/100/)?
Your problem is here:
array_main[i] = (char) decimal % 2 + '0';
You are casting decimal to char and it is swiping off the high-order bits, so that in some cases it becomes negative. % applied to a negative number is negative, hence you get one character before 0 in the ASCII chart, which is /.
I would also like to say that I think your macros WRITEL and WRITE qualify as preprocessor abuse. :-)
It must be array_main[i] = (char) (decimal % 2 + '0'); (note the parentheses). But anyway, the code is horrible, please write it again from scratch.
I haven't tried to analyze all your code in detail, but just glancing at it and seeing delete [] array_main; in two places makes me suspicious. The length of the code makes me suspicious as well. Converting a number to binary should take about two or three lines of code; when I see code something like ten times that long, I tend to think that analyzing it in detail isn't worth the trouble -- if I had to do it, I'd just start over...
Edit: as to how to do the job better, my immediate reaction would be to start with something on this general order:
// warning: untested code.
std::string dec2str(unsigned input) {
std::deque<char> buffer;
while (input) {
buffer.push_front((input & 1)+'0');
input >>= 1;
}
return std::string(&buffer[0], &buffer[0]+buffer.size());
}
While I haven't tested this, it's simple enough that I'd be surprised if there were any errors above the level of simple typos (and it's short enough that there doesn't seem to be room to hide more than one or two of those, at very most).
Related
Given the binary representation of an integer as a string s, return the number of steps to reduce it to 1 under the following rules:
If the current number is even, you have to divide it by 2.
If the current number is odd, you have to add 1 to it.
It is guaranteed that you can always reach one for all test cases.
Step 1) 13 is odd, add 1 and obtain 14.
Step 2) 14 is even, divide by 2 and obtain 7.
Step 3) 7 is odd, add 1 and obtain 8.
Step 4) 8 is even, divide by 2 and obtain 4.
Step 5) 4 is even, divide by 2 and obtain 2.
Step 6) 2 is even, divide by 2 and obtain 1.
My input = 1111011110000011100000110001011011110010111001010111110001
Expected output = 85
My output = 81
For the above input, the output is supposed to be 85. But my output shows 81. For other test cases it
seems to be giving the right answer. I have been trying all possible debugs, but I am stuck.
#include <iostream>
#include <string.h>
#include <vector>
#include <bits/stdc++.h>
using namespace std;
int main()
{
string s =
"1111011110000011100000110001011011110010111001010111110001";
long int count = 0, size;
unsigned long long int dec = 0;
size = s.size();
// cout << s[size - 1] << endl;
for (int i = 0; i < size; i++)
{
// cout << pow(2, size - i - 1) << endl;
if (s[i] == '0')
continue;
// cout<<int(s[i])-48<<endl;
dec += (int(s[i]) - 48) * pow(2, size - 1 - i);
}
// cout << dec << endl;
// dec = 278675673186014705;
while (dec != 1)
{
if (dec % 2 == 0)
dec /= 2;
else
dec += 1;
count += 1;
}
cout << count;
return 0;
}
This line:
pow(2, size - 1 - i)
Can face precision errors as pow takes and returns doubles.
Luckily, for powers base 2 that won't overflow unsigned long longs, we can simply use bit shift (which is equivalent to pow(2, x)).
Replace that line with:
1LL<<(size - 1 - i)
So that it should look like this:
dec += (int(s[i]) - 48) * 1ULL<<(size - 1 - i);
And we will get the correct output of 85.
Note: as mentioned by #RSahu, you can remove (int(s[i]) - 48), as the case where int(s[i]) == '0' is already caught in an above if statement. Simply change the line to:
dec += 1ULL<<(size - 1 - i);
The core problem has already been pointed out in answer by #Ryan Zhang.
I want to offer some suggestions to improve your code and make it easier to debug.
The main function has two parts -- first part coverts a string to number and the second part computes the number of steps to get the number to 1. I suggest creating two helper functions. That will allow you to debug each piece separately.
int main()
{
string s = "1111011110000011100000110001011011110010111001010111110001";
unsigned long long int dec = stringToNumber(s);
cout << "Number: " << dec << endl;
// dec = 278675673186014705;
int count = getStepsTo1(dec);
cout << "Steps to 1: " << count << endl;
return 0;
}
Iterate over the string from right to left using std::string::reverse_iterator. That will obviate the need for size and use of size - i - 1. You can just use i.
unsigned long long stringToNumber(string const& s)
{
size_t i = 0;
unsigned long long num = 0;
for (auto it = s.rbegin(); it != s.rend(); ++it, ++i )
{
if (*it != '0')
{
num += 1ULL << i;
}
}
return num;
}
Here's the other helper function.
int getStepsTo1(unsigned long long num)
{
long int count = 0;
while (num != 1 )
{
if (num % 2 == 0)
num /= 2;
else
num += 1;
count += 1;
}
return count;
}
Working demo: https://ideone.com/yerRfK.
To generate a UFI number, I use a bitset of size 74. To perform step 2 of UFI generation, I need to convert this number:
9 444 732 987 799 592 368 290
(10000000000000000000000000000101000001000001010000011101011111100010100010)
into:
DFSTTM62QN6DTV1
by converting the first representation to base 31 and getting the equivalent chars from a table.
#define PAYLOAD_SIZE 74
// payload = binary of 9444732987799592368290
std::bitset<PAYLOAD_SIZE> bs_payload(payload);
/*
perform modulo 31 to obtain:
12(D), 14(F), 24(S), 25(T), 25, 19, 6, 2, 22, 20, 6, 12, 25, 27, 1
*/
Is there a way to perform the conversion on my bitset without using an external BigInteger library?
Edit: I finally done a BigInteger class even if the Cheers and hth. - Alf's solution works like a charm
To get modulo 31 of a number you just need to sum up the digits in base 32, just like how you calculate modulo 3 and 9 of a decimal number
unsigned mod31(std::bitset<74> b) {
unsigned mod = 0;
while (!b.none()) {
mod += (b & std::bitset<74>(0x1F)).to_ulong();
b >>= 5;
}
while (mod > 31)
mod = (mod >> 5) + (mod & 0x1F);
return mod;
}
You can speedup the modulo calculation by running the additions in parallel like how its done here. The similar technique can be used to calculate modulo 3, 5, 7, 15... and 231 - 1
C - Algorithm for Bitwise operation on Modulus for number of not a power of 2
Is there any easy way to do modulus of 2^32 - 1 operation?
Logic to check the number is divisible by 3 or not?
However since the question is actually about base conversion and not about modulo as the title said, you need to do a real division for this purpose. Notice 1/b is 0.(1) in base b + 1, we have
1/31 = 0.000010000100001000010000100001...32 = 0.(00001)32
and then N/31 can be calculated like this
N/31 = N×2-5 + N×2-10 + N×2-15 + ...
uint128_t result = 0;
while (x)
{
x >>= 5;
result += x;
}
Since both modulo and division use shift-by-5, you can also do both them together in a single loop.
However the tricky part here is how to round the quotient properly. The above method will work for most values except some between a multiple of 31 and the next power of 2. I've found the way to correct the result for values up to a few thousands but yet to find a generic way for all values
You can see the same shift-and-add method being used to divide by 10 and by 3. There are more examples in the famous Hacker's Delight with proper rounding. I didn't have enough time to read through the book to understand how they implement the result correction part so maybe I'll get back to this later. If anyone has any idea to do that it'll be grateful.
One suggestion is to do the division in fixed-point. Just shift the value left so that we have enough fractional part to round later
uint128_t result = 0;
const unsigned num_fraction = 125 - 75 // 125 and 75 are the nearest multiple of 5
// or maybe 128 - 74 will also work
uint128_t x = UFI_Number << num_fraction;
while (x)
{
x >>= 5;
result += x;
}
// shift the result back and add the fractional bit to round
result = (result >> num_fraction) + ((result >> (num_fraction - 1)) & 1)
Note that your result above is incorrect. I've confirmed the result is CEOPPJ62MK6CPR1 from both Yaniv Shaked's answer and Wolfram alpha unless you use different symbols for the digits
This code seems to work. To guarantee the result I think you need to do additional testing. E.g. first with small numbers where you can compute the result directly.
Edit: Oh, now I noticed you posted the required result digits, and they match. Means it's generally good, but still not tested for corner cases.
#include <assert.h>
#include <algorithm> // std::reverse
#include <bitset>
#include <vector>
#include <iostream>
using namespace std;
template< class Type > using ref_ = Type&;
namespace base31
{
void mul2( ref_<vector<int>> digits )
{
int carry = 0;
for( ref_<int> d : digits )
{
const int local_sum = 2*d + carry;
d = local_sum % 31;
carry = local_sum / 31;
}
if( carry != 0 )
{
digits.push_back( carry );
}
}
void add1( ref_<vector<int>> digits )
{
int carry = 1;
for( ref_<int> d : digits )
{
const int local_sum = d + carry;
d = local_sum % 31;
carry = local_sum / 31;
}
if( carry != 0 )
{
digits.push_back( carry );
}
}
void divmod2( ref_<vector<int>> digits, ref_<int> mod )
{
int carry = 0;
for( int i = int( digits.size() ) - 1; i >= 0; --i )
{
ref_<int> d = digits[i];
const int divisor = d + 31*carry;
carry = divisor % 2;
d = divisor/2;
}
mod = carry;
if( digits.size() > 0 and digits.back() == 0 )
{
digits.resize( digits.size() - 1 );
}
}
}
int main() {
bitset<74> bits(
"10000000000000000000000000000101000001000001010000011101011111100010100010"
);
vector<int> reversed_binary;
for( const char ch : bits.to_string() ) { reversed_binary.push_back( ch - '0' ); }
vector<int> base31;
for( const int bit : reversed_binary )
{
base31::mul2( base31 );
if( bit != 0 )
{
base31::add1( base31 );
}
}
{ // Check the conversion to base31 by converting back to base 2, roundtrip:
vector<int> temp31 = base31;
int mod;
vector<int> base2;
while( temp31.size() > 0 )
{
base31::divmod2( temp31, mod );
base2.push_back( mod );
}
reverse( base2.begin(), base2.end() );
cout << "Original : " << bits.to_string() << endl;
cout << "Reconstituted: ";
string s;
for( const int bit : base2 ) { s += bit + '0'; cout << bit; }; cout << endl;
assert( s == bits.to_string() );
}
cout << "Base 31 digits (msd to lsd order): ";
for( int i = int( base31.size() ) - 1; i >= 0; --i )
{
cout << base31[i] << ' ';
}
cout << endl;
cout << "Mod 31 = " << base31[0] << endl;
}
Results with MinGW g++:
Original : 10000000000000000000000000000101000001000001010000011101011111100010100010
Reconstituted: 10000000000000000000000000000101000001000001010000011101011111100010100010
Base 31 digits (msd to lsd order): 12 14 24 25 25 19 6 2 22 20 6 12 25 27 1
Mod 31 = 1
I did not compile the psuedo code, but you can get the generate understanding of how to convert the number:
// Array for conversion of value to base-31 characters:
char base31Characters[] =
{
'0',
'1',
'2',
...
'X',
'Y'
};
void printUFINumber(__int128_t number)
{
string result = "";
while (number != 0)
{
var mod = number % 31;
result = base31Characters[mod] + result;
number = number / 31;
}
cout << number;
}
I would like to count the number of decimal digits after the radix point of a floating point number.
The problem obviously raise when the real number doesn't have a representation in the binary system, like 3.5689113.
I am wondering - if for example someone write this real in a source code - if it is possible to get the number 7 namely the number of digits after the radix point
the naive following code for example doesn't work :
int main()
{
double num = 3.5689113;
int count = 0;
num = abs(num);
num = num - int(num);
while ( abs(num) >
0.0000001 )
{
num = num * 10;
count = count + 1;
num = num - int(num);
}
std::cout << count; //48
std::cin.ignore();
}
When something like that doesn't work, you try to print the numbers.
I did so here, and I found you had some floating number precision issues.
I changed the int rounding to ceil rounding and it worked like a charm.
Try putting the ints back and you'll see :)
EDIT: a better strategy than using ceils (which can give the same rounding problems) is to just round the numbers to the nearest integer. You can do that with floor(myNumber+0.5).
Here's the modified code
int main()
{
double num = 3.56891132326923333;
// Limit to 7 digits
num = floor(num*10000000 + 0.5)/10000000;
int count = 0;
num = abs(num);
num = num - floor(num+0.5);
while ( abs(num) >
0.0000001 )
{
cout << num << endl;
num = num * 10;
count = count + 1;
num = num - floor(num+0.5);
}
std::cout << count; //48
std::cin.ignore();
return 0;
}
To prevent the errors introduced by floating point approximation, convert the number to an integer at the earliest possible opportunity and work with that.
double num = 3.5689113;
int count = 7; // a maximum of 7 places
num = abs(num);
int remainder = int(0.5 + 10000000 * (num - int(num)));
while ( remainder % 10 == 0 )
{
remainder = remainder / 10;
--count;
}
For a floating point type T you can get up to std::numeric_limits<T>::digits10 digits restored exactly. Thus, to determine the position of the last non-zero fractional digits you'd use this value as a precision and format the number. To avoid the output using exponent notation you need to set the formatting flags to std::ios_base::fixed and account for the number of non-fractional digits:
std::ostringstream out;
int non_fraction(std::abs(value) < std::numeric_limits<double>::epsilon()
? 1: (1 + std::log(std::abs(value)) / std::log(10)));
out << std::setprecision(std::numeric_limits<double>::digits10 - non_fraction)
<< std::fixed
<< value;
If there is a decimal point, you just need to count the number of digits up to the trailing sequence of zeros.
I would recommend converting to a string, then looping over it and counting how many chars occur after you hit the period. Below is a sample (may need some minor tinkering, been awhile since I've done this in C++);
bool passedRadix = false
int i = 0; // for counting decimals
std::ostringstream strs;
strs << dbl; // dbl is 3.415 or whatever you're counting
std::string str = strs.str();
for(char& c : str) {
if (passedRadix == true)
i++;
if (c == '.')
passedRadix = true;
}
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, visit the help center.
Closed 11 years ago.
An interview question:
Make a program which takes input 'N'(unsigned long) and prints two columns, 1st column prints numbers from 1 to N (in hexadecimal format) and second column prints the number of 1s in the binary representation of the number in the left column. Condition is that this program should not count 1s (so no computations 'per number' to get 1s/ no division operators).
I tried to implement this by leveraging fact that No of 1s in 0x0 to 0xF can be re-used to generate 1s for any number. I am pasting code ( basic one without error checking.) Its giving correct results but I am not happy with space usage. How can I improve on this?
( Also I am not sure if its what interviewer was looking for).
void printRangeFasterWay(){
uint64_t num = ~0x0 ;
cout << " Enter upper number " ;
cin >> num ;
uint8_t arrayCount[] = { 0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4} ;
// This array will store information needed to print
uint8_t * newCount = new uint8_t[num] ;
uint64_t mask = 0x0 ;
memcpy(newCount, &arrayCount[0], 0x10) ;
uint64_t lower = 0;
uint64_t upper = 0xF;
uint64_t count = 0 ;
uint32_t zcount= 0 ;
do{
upper = std::min(upper, num) ;
for(count = lower ; count <= upper ; count++){
newCount[count] = (uint32_t)( newCount[count & mask] + newCount[(count & ~mask)>>(4*zcount)]) ;
}
lower += count ;
upper |= (upper<<4) ;
mask = ((mask<<4) | 0xF ) ;
zcount++ ;
}while(count<=num) ;
for(uint64_t xcount=0 ; xcount <= num ; xcount++){
cout << std::hex << " num = " << xcount << std::dec << " number of 1s = " << (uint32_t)newCount[xcount] << endl;
}
}
Edited to add sample run
Enter upper number 18
num = 0 number of 1s = 0
num = 1 number of 1s = 1
num = 2 number of 1s = 1
num = 3 number of 1s = 2
num = 4 number of 1s = 1
num = 5 number of 1s = 2
num = 6 number of 1s = 2
num = 7 number of 1s = 3
num = 8 number of 1s = 1
num = 9 number of 1s = 2
num = a number of 1s = 2
num = b number of 1s = 3
num = c number of 1s = 2
num = d number of 1s = 3
num = e number of 1s = 3
num = f number of 1s = 4
num = 10 number of 1s = 1
num = 11 number of 1s = 2
num = 12 number of 1s = 2
I have a slightly different approach which should solve your memory problem. Its based on the fact that the bitwise operation i & -i gives you the smallest power of two in the number i. For example, for i = 5, i & -i = 1, for i = 6, i & -i = 2. Now, for code:
void countBits(unsigned N) {
for (int i = 0;i < N; i ++)
{
int bits = 0;
for (int j = i; j > 0; j= j - (j&-j))
bits++;
cout <<"Num: "<<i <<" Bits:"<<bits<<endl;
}
}
I hope I understood your question correctly. Hope that helps
Edit:
Ok, try this - this is dynamic programming without using every bit in every number:
void countBits(unsigned N) {
unsigned *arr = new unsigned[N + 1];
arr[0]=0;
for (int i = 1;i <=N; i ++)
{
arr[i] = arr[i - (i&-i)] + 1;
}
for(int i = 0; i <=N; i++)
cout<<"Num: "<<i<<" Bits:"<<arr[i]<<endl;
}
Hopefully, this works better
Several of the answers posted so far make use of bit shifting (just another word for division by 2) or
bit masking. This stikes me as a bit of a cheat. Same goes for using the '1' bit count in a 4 bit pattern then
matching by chunks of 4 bits.
How about a simple recursive solution using an imaginary binary tree of bits. each left branch contains a '0', each
right branch contains a '1'. Then do a depth first traversal counting the number of 1 bits on the way down. Once
the bottom of the tree is reached add one to the counter, print out the number of 1 bits found so far, back out
one level and recurse again.
Stop the recursion when the counter reaches the desired number.
I am not a C/C++ programmer, but here is a REXX solution that should translate without much imagination. Note
the magic number 32 is just the number of bits in an Unsigned long. Set it to anything
/* REXX */
SAY 'Stopping number:'
pull StopNum
Counter = 0
CALL CountOneBits 0, 0
return
CountOneBits: PROCEDURE EXPOSE Counter StopNum
ARG Depth, OneBits
If Depth = 32 then Return /* Number of bits in ULong */
if Counter = StopNum then return /* Counted as high as requested */
call BitCounter Depth + 1, OneBits /* Left branch is a 0 bit */
call BitCounter Depth + 1, OneBits + 1 /* Right branch is a 1 bit */
Return
BitCounter: PROCEDURE EXPOSE Counter StopNum
ARG Depth, OneBits
if Depth = 32 then do /* Bottom of binary bit tree */
say D2X(Counter) 'contains' OneBits 'one bits'
Counter = Counter + 1
end
call CountOneBits Depth, OneBits
return
Results:
Stopping number:
18
0 contains 0 one bits
1 contains 1 one bits
2 contains 1 one bits
3 contains 2 one bits
4 contains 1 one bits
5 contains 2 one bits
6 contains 2 one bits
7 contains 3 one bits
8 contains 1 one bits
9 contains 2 one bits
A contains 2 one bits
B contains 3 one bits
C contains 2 one bits
D contains 3 one bits
E contains 3 one bits
F contains 4 one bits
10 contains 1 one bits
11 contains 2 one bits
This answer is resonably efficient in time and space.
Can be done relatively trivially in constant time with the appropriate bit switching. No counting of 1s and no divisions. I think you were on the right track with keeping the array of known bit values:
int bits(int x)
{
// known bit values for 0-15
static int bc[16] = {0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4};
// bit "counter"
int b = 0;
// loop iterator
int c = 0;
do
{
// get the last 4 bits in the number
char lowc = static_cast<char>(x & 0x0000000f);
// find the count
b += bc[lowc];
// lose the last four bits
x >>= 4;
++c;
// loop for each possible 4 bit combination,
// or until x is 0 (all significant bits lost)
}
while(c < 8 && x > 0);
return b;
}
Explanation
The following algorithm is like yours, but expands on the idea (if I understood your approach correctly.) It does not do any computation 'per number' as directed by the question, but instead uses a recursion that exists between sequences of lengths that are powers of 2. Basically, the observation is that for the sequence 0, 1,..,2^n-1 , we can use the sequence 0, 1, ...,2^(n-1)-1 in the following way.
Let f(i) be the number of ones in number i then f(2^(n-1)+i)=f(i)+1 for all 0<=i<2^(n-1). (Verify this for yourself)
Algorithm in C++
#include <stdio.h>
#include <stdlib.h>
int main( int argc, char *argv[] )
{
const int N = 32;
int* arr = new int[N];
arr[0]=0;
arr[1]=1;
for ( int i = 1; i < 15; i++ )
{
int pow2 = 1 << i;
int offset = pow2;
for ( int k = 0; k < pow2; k++ )
{
if ( offset+k >= N )
goto leave;
arr[offset+k]=arr[k]+1;
}
}
leave:
for ( int i = 0; i < N; i++ )
{
printf( "0x%8x %16d", i, arr[i] );
}
delete[] arr;
return EXIT_SUCCESS;
}
Note that in the for loop
for ( int i = 0; i < 15; i++ )
there may be overflow into negative numbers if you go higher than 15, otherwise use unsigned int's if you want to go higher than that.
Efficiency
This algorithm runs in O(N) and uses O(N) space.
Here is an approach that has O(nlogn) time complexity and O(1) memory usage. The idea is to get the Hex equivalent of the number and iterate over it to get number of ones per Hex digit.
int oneCount[] = { 0,1,1,2,1,2,2,3,1,2,2,3,2,3,3,4};
int getOneCount(int n)
{
char inStr[70];
sprintf(inStr,"%X",n);
int i;
int sum=0;
for(i=0; inStr[i];i++)
{
if ( inStr[i] > '9' )
sum += oneCount[inStr[i]-'A' + 10];
else
sum+= oneCount[inStr[i] -'0'];
}
return sum;
}
int i,upperLimit;
cin>>upperLimit;
for(i=0;i<=upperLimit;i++)
{
cout << std::hex << " num = " << i << std::dec << " number of 1s = " << getOneCount(i) << endl;
}
enum bit_count_masks32
{
one_bits= 0x55555555, // 01...
two_bits= 0x33333333, // 0011...
four_bits= 0x0f0f0f0f, // 00001111....
eight_bits= 0x00ff00ff, // 0000000011111111...
sixteen_bits= 0x0000ffff, // 00000000000000001111111111111111
};
unsigned int popcount32(unsigned int x)
{
unsigned int result= x;
result= (result & one_bits) + (result & (one_bits << 1)) >> 1;
result= (result & two_bits) + (result & (two_bits << 2)) >> 2;
result= (result & four_bits) + (result & (four_bits << 4)) >> 4;
result= (result & eight_bits) + (result & (eight_bits << 8)) >> 8;
result= (result & sixteen_bits) + (result & (sixteen_bits << 16)) >> 16;
return result;
}
void print_range(unsigned int low, unsigned int high)
{
for (unsigned int n= low; unsigned int n<=high; ++n)
{
cout << std::hex << " num = " << xcount << std::dec << " number of 1s = " << popcount32(n) << endl;
}
}
Could anyone please tell me how to check what number I've got from a * b? Which is I would like to know every part of this number so for example if the result from this expression would be 25 I would like to know that first digit is two and second digit is five.
perhaps a little overkill... but even works with doubles
#include <sstream>
#include <iostream>
int main()
{
double a = 5.2;
double b = 7;
double z = a*b;
std::stringstream s;
s << z;
for (int i = 0; i < s.str().length(); i++)
std::cout << i << ": " << s.str()[i] << std::endl;
return 0;
}
a mod 10 == last digit of a
a / 10 == a without its last digit
So, for 25:
25 % 10 == 5 => 5 is the last digit of 25
25 / 10 == 2
2 % 10 == 2 => 2 is the first digit of 25
You can use these in a while loop to get each digit.
while (num > 0)
{
digit = num % 10;
// digit is now the current digit, counting from the right towards the left.
num /= 10;
}
int val = res;
while( val > 0 )
{
std::cout << val % 10 << endl;
val /= 10;
}
You have to get the result of the integer division by the appropriate power of ten.
int exp = std::floor( std::log10( num ) );
int first_digit = num / int( std::pow( 10.0, exp ) );
This is an (inefficient) way to get the first digit directly. It would be better to iterate starting from the last.
char str[30];
sprintf(str,"%d",a*b);
int ndigits = strlen(str);
There you have all digits of your value in the string, and the number of digits in ndigits.
e.g. if a*b = 25 you get
ndigits==2
str[ndigits-1]=='5'
str[ndigits-2]=='2'
What do you want this for?
There's probably an underlying misunderstanding here. The result of the multiplication will most likely be 0x00000019. (Number of leading zeroes will differ). The second step, converting it to canonical decimal will yield "25".
It's important to realize that computers, unlike normal humans, don't do their math in decimal but in binary. Hence, if you want to check a property like "last decimal digit of a number", it's not directly available to them.
Just remember, that e.g. 2101 is basically just 2*10^3 + 1*10^2 + 0*10^1 + 1*10^0.