division of array on some criterion [closed] - c++

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in this code i try to divide the a[5] into two arrays on the criterion of stored data in the array .......
and store the index of the array a[5] to other arrays to show these index contain different data elements
but i doesn't work for me
#include <iostream>
using namespace std;
void printarray(int b[], int count)
{
int i;
for(i=0;i<count;i++)
cout<<b[i]<<endl;
}
void main()
{
int a[5]={1,0,0,1,1};
int array[5][5]=
{
{0,5,0,4,0},
{0,0,6,0,7},
{0,0,0,0,8},
{0,0,0,0,10},
{0,0,0,0,0}
};
int count=0;
int counti=0;
int C1=0;
int i;
for(i=0;i<5;i++)
{
if(C1==a[i])
{
count++;
}
else
{
counti++;
}
}
int *b= new int[count];
int *c= new int[counti];
for(i=0;i<5;i++)
{
if(C1==a[i])
{
b[i]=i;
}
else
{
c[i]=i;
}
}
printarray(b,count);
}
the code display the grabage values... plz help me
its show the following result
-842151450
1

The first i was 1 , so b will contain {1, 2}. where ( b[1] = 1, b[2] = 2 )
when you loop through b to print all elements you start from index 0 although b started from index 1.
you can fix index using (j, k instead of i).
int *b = new int[count];
int *c = new int[counti];
int j, k;
j = k = 0;
for (i = 0; i<5; i++)
{
if (C1 == a[i])
{
b[j++] = i;
}
else
{
c[k++] = i;
}
}
printarray(b, count);

Related

Bubble sorting using pointers but I have to use pointers to traverse as well [closed]

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I have to create a bubble sort program using pointers but instead of using i and j for iterations, I have to use pointers.
#include<iostream>
using namespace std;
int main() {
int size = 6;
int size1 = size;
int arr[] = { 8, 6, 11, 3, 15, 5 };
int* myarr = arr;
int* endptr = myarr + size;
int* endptr2 = myarr + size;
for (myarr; myarr < endptr; myarr++) {
for (myarr; myarr < endptr2; myarr++){
if (*myarr > *(myarr + 1)) {
swap(*myarr, *(myarr + 1));
}
}
endptr2--;
}
}
The first loop is working good but I am not able to iterate the second loop for bubble sort.
Something like this?
#include <iostream>
#include <vector>
void bubblesort( int arr[], int N ) {
if ( N<2 ) return;
for ( int* endptr = &arr[N-1]; endptr>arr; --endptr ) {
for ( int* p = arr; p<endptr; ++p ) {
if ( p[0] > p[1] ) {
std::swap(p[0],p[1]);
}
}
}
}
int main() {
std::vector<int> values = {10,3,8,1,2,3,7,9};
bubblesort( values.data(), values.size() );
for ( int value : values ) {
std::cout << value << " ";
}
std::cout << std::endl;
}
Produces
1 2 3 3 7 8 9 10
https://godbolt.org/z/56roK56do

Could someone show me how this is implemented in main()? (question on void pointers) [closed]

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I got the below snippet from Algorithms in a nut shell
void sortPointers (void **ar, int n,
int (*cmp)(const void *, const void *)) {
int j;
for (j = 1; j < n; j++) {
int i = j-1;
void *value = ar[j];
while (i >= 0 && cmp (ar[i], value) > 0) {
ar[i+1] = ar[i];
i--;
}
ar[i+1] = value;
}
}
https://www.amazon.com/Algorithms-Nutshell-OReilly-George-Heineman/dp/059651624X
They do not provide the main() implementation of
sortPointers
so i have some problems figuring out what does **ar do
when i attempted to do a test code on
**arrPtr = x
it returns the error that you cannot cast void ** on a int *.
this surprises me as the book clearly says you feed an array into the function.
int main()
{
var x[3] = { 2 , 4 , 3};
void **arrPtr = x[0];
return 0;
}
a side question as well.
void *value = ar[j];
is this a unneeded step? the CMP function was able to take ar[i] as a argument, shouldnt it be able to take ar[j] as is?
In C we have the function qsort which is a generic function to sort arrays. It can sort all kind of arrays (e.g. arrays of int, arrays of double and even arrays of custom structs). All it requires is that the user provide a "compare" function for comparing two elements.
The sortPointers seems to be pretty much the same except it does not sort arrays of elements but instead sorts an array of pointers to elements.
As far a I can see the idea is to use it like:
#include <stdio.h>
#include <stdlib.h>
int cmp(const void * a, const void * b)
{
int* pa = (int*)a;
int* pb = (int*)b;
if (*pa > *pb) return 1;
if (*pa < *pb) return -1;
return 0;
}
void sortPointers (void **ar, int n,
int (*cmp)(const void *, const void *))
{
int j;
for (j = 1; j < n; j++) {
int i = j-1;
void *value = ar[j];
while (i >= 0 && cmp (ar[i], value) > 0) {
ar[i+1] = ar[i];
i--;
}
ar[i+1] = value;
}
}
void pp(int **ar, int n)
{
for(int i=0; i<n; ++i)
printf("Address %p holds the value %p and points to %d, i.e. arr[%d] points to %d\n", (void*)(&ar[i]), (void*)ar[i], *ar[i], i, *ar[i]);
}
#define ELEM 3
int main(void)
{
int* arr[3];
for(int i=0; i<ELEM; ++i) arr[i] = malloc(sizeof(int));
*arr[0] = 5;
*arr[1] = 8;
*arr[2] = 2;
pp(arr, ELEM);
sortPointers((void**)arr, ELEM, cmp);
printf("------------------------\n");
pp(arr, ELEM);
for(int i=0; i<ELEM; ++i) free(arr[i]);
return 0;
}
Output:
Address 0x7fff9a7d0270 holds the value 0xeeb010 and points to 5, i.e. arr[0] points to 5
Address 0x7fff9a7d0278 holds the value 0xeeb030 and points to 8, i.e. arr[1] points to 8
Address 0x7fff9a7d0280 holds the value 0xeeb050 and points to 2, i.e. arr[2] points to 2
------------------------
Address 0x7fff9a7d0270 holds the value 0xeeb050 and points to 2, i.e. arr[0] points to 2
Address 0x7fff9a7d0278 holds the value 0xeeb010 and points to 5, i.e. arr[1] points to 5
Address 0x7fff9a7d0280 holds the value 0xeeb030 and points to 8, i.e. arr[2] points to 8
However, the whole function seems to be a waste of time. The standard qsort can do this for you so why write a special function? As written above qsort can sort all kind of arrays so it can also sort an array of pointers. The compare function just needs to be a bit different. Simply use qsort like:
// Compare function
int cmp_qsort(const void * a, const void * b)
{
int** pa = (int**)a;
int** pb = (int**)b;
if (**pa > **pb) return 1;
if (**pa < **pb) return -1;
return 0;
}
// Call from main like:
qsort(arr, ELEM, sizeof(int*), cmp_qsort);
The output will be the same (except for the address that change every time you run it) and you don't need a custom sort function like sortPointers.

newbie ask about decimal to binary in c++ [closed]

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this program suppose to convert decimal to binary but somehow i screw it up
can some one point out the error for me?
thanks a lot
#include<conio.h>
#include<stdio.h>
int main(){
int a;
int b[20];
int q = 0;
printf("decimal : ");scanf("%d",&a);
while(a>0)) {
b[q]=a%2;
a=a/2;
q++;
}while(a>0);
printf("binary : ");
for (int i = q-1; i>=0;i--){
printf("%d",b[q]);
}
}
Corrected code is:
#include<conio.h>
#include<stdio.h>
int main(){
int a;
int b[20];
int q = 0;
printf("decimal : ");scanf("%d",&a);
while(a>0) {
b[q]=a%2;
a=a/2;
q++;
}
printf("binary : ");
for (int i = q-1; i>=0;i--){
printf("%d",b[i]);
}
}
You were printing b[q] instead of b[i]
There are some problems with your code:
you added an extra ")" of the first while;
the second 'while' is useless (the code is being repeated due to the first one)
you are not printing the elements you want (you should use var 'i'), what you are really printing is the value after the last 0/1 (because you are using 'q')
code should look like this:
#include <conio.h>
#include <stdio.h>
int main() {
int a;
int b[20];
int q = 0;
printf("decimal: ");
scanf("%d", &a);
while (a > 0) {
b[q] = a % 2;
a = a / 2;
q++;
}
printf("binary: ");
for (int i = q - 1; i >= 0; i--) {
printf("%d", b[i]);
}
}

C++ unclear output [closed]

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Closed 7 years ago.
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I'm trying to find all the divisors of a number (n) and to add to the array those divisors that are at the 1st power (that appear only once), but I get in output just zeros, what's wrong with my code?
#include<iostream>
using namespace std;
int k,A[100000],n,p,d=2,pozitia=0;
int main()
{
cin>>n;
while(n>1)
{
p=0;
while(n%d==0)
{
p=p+1;
n=n/d;
}
if (p==1) { A[pozitia]=d; pozitia++; }
d=d+1;
}
for (int i=0;i<=pozitia;i++) cout<<A[pozitia]<<" ";
return 0;
}
You print always the same value:
for (int i=0;i<=pozitia;i++)
cout<<A[pozitia]<<" ";
It should be
for (int i=0;i<pozitia;i++)
cout<<A[i]<<" ";
Also pay attention that it should be i<pozitia and not i<=pozitia because you increment pozitia each time you insert a new value so at the end pozitia will point to a not initialized value in A.
I couldn't follow your logic for computing the divisors. It seems to be much simpler than you make it out to be.
int stop = n/2 + 1;
for ( ; d < stop; ++d )
{
if ( n % d == 0 )
{
A[pozitia]=d;
pozitia++;
}
}
Here's a program that uses that logic.
#include<iostream>
using namespace std;
void printDivisors(int A[], int pozitia)
{
for (int i=0;i<pozitia;i++) cout<<A[i]<<" ";
}
void fun(int n)
{
int A[100000];
int d = 2;
int pozitia=0;
int stop = n/2 + 1;
for ( ; d < stop; ++d )
{
if ( n % d == 0 )
{
A[pozitia]=d;
pozitia++;
}
}
printDivisors(A, pozitia);
}
int main()
{
int n;
cin>>n;
fun(n);
return 0;
}
The output for input of 100:
2 4 5 10 20 25 50

How to make all array elements accessible [closed]

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I've been trying to make the elements of an array accessible, but I've had no success so far. This is the code, and I've created it due to the given assignment.
#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;
class Matrix_1D
{
private:
int *p2values;
int num_elements;
public:
Matrix_1D(int *p2v, int n); // CTOR
~Matrix_1D(); // DTOR
void show();
};
Matrix_1D::Matrix_1D(int *p2v, int n)
{
n = sizeof(p2v)/sizeof(int); // the problem comes from the fact that sizeof(p2v) = 4 bytes, and not the length of the entire array!!!
num_elements = n;
p2values = new int [n];
for(int i = 0; i<num_elements; i++)
p2values[i] = p2v[i];
}
Matrix_1D::~Matrix_1D()
{
delete [] p2values;
}
void Matrix_1D::show()
{
for(int i=0; i<num_elements; i++)
cout << p2values[i] << endl;
}
int main()
{
int array_a[] = {5,3,5};
Matrix_1D fkt_1D_a(array_a, sizeof(array_a)/sizeof(int));
fkt_1D_a.show();
system("pause");
return 0;
}
Matrix_1D::Matrix_1D(int *p2v, int n)
{
n = sizeof(p2v)/sizeof(int); // the problem comes from the fact that sizeof(p2v) = 4 bytes, and not the length of the entire array!!!
num_elements = n;
p2values = new int [n];
for(int i = 0; i<num_elements; i++)
p2values[i] = p2v[i];
}
As you state the sizeof p2v is the size of the pointer so you have no idea how large the array is. Instead, use the parameter that is passed in and don't overwrite it:
Matrix_1D::Matrix_1D(int *p2v, int n)
{
// you don't need the first line at all.
num_elements = n;
p2values = new int [n];
for(int i = 0; i<num_elements; i++)
p2values[i] = p2v[i];
}
The proper C++ way to get the size of your int array is to use a template:
template <typename T, size_t N>
size_t size(T (&)[N]) {
return N; // size of array
}