How to make space between array values in printing? - c++

I'm interested, how could i get same result in C++. For this C code:
for(i=0;i<n;i++)
printf("%4d",array[i]);
This will create 4 space gap between my values from array.
Is there something similar in C++?

The same code works in C++:
const int n = 10;
int array[n] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
for (int i=0;i<n;i++)
printf("%4d",array[i]);
But if you're looking for more a C++-esque way of doing things, you can use std::cout and std::setw:
#include <iostream> // cout
#include <iomanip> // setw
int main()
{
int array[10] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
for (auto n : array)
{
std::cout << std::setw(4) << n;
}
}

Related

Find unique element in sorted array using c++

I am trying to find unique element from the array these is question
Input : arr[] = {1, 2, 2, 3, 4, 4, 4, 5, 5}
Output : arr[] = {1, 2, 3, 4, 5}
They give me correct output but why they give 0 at the end in output:
these is my output:
{1,2,3,4,5,0}
Code:
#include<iostream>
using namespace std;
int main(){
int arr[] = {1, 2, 2, 3, 4, 4, 4, 5, 5};
int n=sizeof(arr)/sizeof(arr[0]);
int c=0;
for(int j=0;j<=n;j++){
if(arr[j]!=arr[j+1]){
cout<<arr[j];
}
}
}
Except for std::cout, you code is much more C than ++.
std::unique of the C++ Standard Library does exactly what you want. There is no need to re-implement this.
Next there is the erase-remove idiom to delete the superfluous elements.
For the output, you can use std::for_each() or at least a range-based for loop.
And also, you don't want using namespace std;
A more modern solution looks like this:
#include <iostream>
#include <algorithm>
#include <vector>
int main(){
std::vector<int> arr {1, 2, 2, 3, 4, 4, 4, 5, 5};
auto last = std::unique(arr.begin(), arr.end());
arr.erase(last, arr.end());
std::for_each(arr.begin(), arr.end(), [](int n){std::cout << n << std::endl;} );
}
Try it on Godbolt.
problem is in for loop becouse you use less or equal to n.
you need to use just less then n becouse array starts from zero that means you asking for sixth element that do not have alocalizated in memory
now it should be correct
#include<iostream>
using namespace std;
int main() {
int arr[] = {1, 2, 2, 3, 4, 4, 4, 5, 5};
int n=sizeof(arr)/sizeof(arr[0]);
int c=0;
for(int j=0; j<n; j++) {
if (arr[j]!=arr[j+1]) {
cout<<arr[j];
}
}
}

C++ - Sort array in descending order not working

int array[6] = {5, 10, 2, 5, 4, 4}
std::sort(array, array + (sizeof array / sizeof array[0]), std::greater<int>());
I am trying to sort the above array in descending order, but when I run the sort function on it I am getting the following:
{10, 5, 2, 5, 4, 4}
Any ideas?
EDIT: The problem was with surrounding code I had. The code posted here is actually correct.. Sorry.
Based on the example of the reference, what you have should work:
#include <iostream> // std::cout
#include <algorithm> // std::sort
#include <vector> // std::vector
int main (void) {
int array[6] = {5, 10, 2, 5, 4, 4};
std::sort(array, array + (sizeof array / sizeof array[0]), std::greater<int>());
for (int i = 0; i < 6; ++i)
std::cout << array[i] << " ";
std::cout << '\n';
return 0;
}
Output:
10 5 5 4 4 2
As you can see, this is the same as your code. See it yourself in the Live Demo.

printing a 2D array inside a function in c++

I have made the following program in c++. I just want to print an array elements. My code is as follows:
#include <iostream>
#include <cstdio>
using namespace std;
#define n 5
double dist[n][n];
void read_distances()
{
for(int i = 0; i < n ; i++)
{
for (int j = 0 ;j < n; j++)
{
cout<<dist[i][j]<<" ";
}
cout<<"\n";
}
}
main()
{
double dist[n][n] =
{
{0, 20, 30, 10, 11},
{15, 0, 16, 4, 2},
{3, 5, 0, 2, 4},
{19, 6, 18, 0, 3},
{16, 4, 7, 16, 0}
};
read_distances();
}
I just wanted to print the dist[][] array inside the read_distances() function. But here I am getting all the values 0 as output. what's the reason of this?
The reason is because you declared the dist array in main(), and you initialized its contents, but the function read_distances() prints the values of a global array called dist. It happens to have the same name as the dist array in main()'s scope, but is a completely different array, and it is never initialized.
EDIT: you asked how to make it work. The easiest way is to pass it as a parameter. After removing the global declaration:
void read_distances(double dist[n][n])
{
// ...
}
and then in your main():
read_distances(dist);
(technically, the parameter to read_distances() is actually double (*)[n], but that's going to be a topic for another day and I didn't want to make this too confusing).
How about this:
#include <iostream>
#include <cstdio>
using namespace std;
#define n 5
void read_distances(double dist[n][n])
{
for(int i = 0; i < n ; i++)
{
for (int j = 0 ;j < n; j++)
{
cout<<dist[i][j]<<" ";
}
cout<<"\n";
}
}
int main()
{
double dist[n][n] =
{
{0, 20, 30, 10, 11},
{15, 0, 16, 4, 2},
{3, 5, 0, 2, 4},
{19, 6, 18, 0, 3},
{16, 4, 7, 16, 0}
};
read_distances(dist);
}
Your code doesn't work because you overshadowed the global version of dist with the local one you created at main. So you either not use a global one, like I do here, and pass the one you create at main() to your printing function; or you fill that array without creating a new array in main().

How do I pass an array to a constructor?

I want to pass an array to a constructor, but only the first value is passed--the rest looks like garbage.
Here's a simplified version of what I'm working on:
#include <iostream>
class board
{
public:
int state[64];
board(int arr[])
{
*state = *arr;
}
void print();
};
void board::print()
{
for (int y=0; y<8; y++)
{
for (int x=0; x<8; x++)
std::cout << state[x + y*8] << " ";
std::cout << "\n";
}
}
int main()
{
int test[64] = {
0, 1, 2, 3, 4, 5, 6, 7,
1, 2, 3, 4, 5, 6, 7, 8,
2, 3, 4, 5, 6, 7, 8, 9,
3, 4, 5, 6, 7, 8, 9,10,
4, 5, 6, 7, 8, 9,10,11,
5, 6, 7, 8, 9,10,11,12,
6, 7, 8, 9,10,11,12,13,
7, 8, 9,10,11,12,13,14 };
board b(test);
b.print();
std::cin.get();
return 0;
}
Can someone explain why this doesn't work and how to properly pass an array? Also, I don't want to copy the array. (And do I really have to indent every line by 4 spaces for code? That's pretty tedious.)
In this case it might be best to use a reference to the array:
class board
{
int (&state)[64];
public:
board(int (&arr)[64])
: state(arr)
{}
// initialize use a pointer to an array
board(int (*p)[64])
: state(*p)
{}
void print();
};
A couple of advantages - no copying of the array, and the compiler will enforce that the correct size array is passed in.
The drawbacks are that the array you initialize the board object with needs to live at least as long as the object and any changes made to the array outside of the object are 'reflected' into the object's state. but those drawbacks occur if you use a pointer to the original array as well (basically, only copying the array will eliminate those drawbacks).
One additional drawback is that you can't create the object using a pointer to an array element (which is what array function parameters 'decay' to if the array size isn't provided in the parameter's declaration). For example, if the array is passed through a function parameter that's really a pointer, and you want that function to be able to create a board object referring to that array.
Attempting to pass an array to a function results in passing a pointer to the first element of the array.
You can't assign arrays, and taking a parameter like T[] is the same as T*. So
*state = *arr;
Is dereferencing the pointers to state and arr and assigning the first element of arr to the first element of state.
If what you want to do is copy the values from one array to another, you can use std::copy:
std::copy(arr, arr + 64, state); // this assumes that the array size will
// ALWAYS be 64
Alternatively, you should look at std::array<int>, which behaves exactly like you were assuming arrays behave:
#include <array>
#include <algorithm>
#include <iostream>
class board
{
public:
std::array<int, 64> state;
board(const std::array<int, 64> arr) // or initialiser list : state(arr)
{
state = arr; // we can assign std::arrays
}
void print();
};
void board::print()
{
for (int y=0; y<8; y++)
{
for (int x=0; x<8; x++)
std::cout << state[x + y*8] << " ";
std::cout << "\n";
}
}
int main()
{
// using this array to initialise the std::array 'test' below
int arr[] = {
0, 1, 2, 3, 4, 5, 6, 7,
1, 2, 3, 4, 5, 6, 7, 8,
2, 3, 4, 5, 6, 7, 8, 9,
3, 4, 5, 6, 7, 8, 9,10,
4, 5, 6, 7, 8, 9,10,11,
5, 6, 7, 8, 9,10,11,12,
6, 7, 8, 9,10,11,12,13,
7, 8, 9,10,11,12,13,14 };
std::array<int, 64> test(std::begin(arr), std::end(arr));
board b(test);
b.print();
std::cin.get();
return 0;
}
#include <iostream>
class board
{
public:
int * state; //changed here, you can also use **state
board(int *arr) //changed here
{
state = arr;
}
void print();
};
void board::print()
{
for (int y=0; y<8; y++)
{
for (int x=0; x<8; x++)
std::cout << *(state + x + y*8) << " "; //changed here
std::cout << "\n";
}
}
int main()
{
int test[64] = {
0, 1, 2, 3, 4, 5, 6, 7,
1, 2, 3, 4, 5, 6, 7, 8,
2, 3, 4, 5, 6, 7, 8, 9,
3, 4, 5, 6, 7, 8, 9,10,
4, 5, 6, 7, 8, 9,10,11,
5, 6, 7, 8, 9,10,11,12,
6, 7, 8, 9,10,11,12,13,
7, 8, 9,10,11,12,13,14 };
board b(test);
b.print();
std::cin.get();
return 0;
}
or you can use it as:
class board
{
public:
int state[64];
board(int arr[])
{
for(int i=0;i<64;++i)
state[i] = arr[i];
}
void print();
};
EDIT 1:
stable solution
class board
{
public:
int * state; //changed here, you can also use **state
board(int *arr) //changed here
{
state = new int[64];
for(int i=0;i<64;++i)
state[i] = arr[i];
}
void print();
};
*arr gives the value that is stored at arr[0] . In c++ , the name of the array is a pointer to the first element in the array.
So when you do *state = *arr , you store the value at arr[0] in the variable state.
Now , if you want to pass the array without having to copy each element explicitly , I suggest that you make another array of the same size in the method which you are calling and then pass the name of the array from the caller , in essence :
methodWhereArrayisPassed(int *arrayName)
{
int arrCopy[64];
arrCopy = arrayName;
// Do more stuff here
}
methodWhichPassesArray()
{
// do stuff here
int arr[] = {
0, 1, 2, 3, 4, 5, 6, 7,
1, 2, 3, 4, 5, 6, 7, 8,
2, 3, 4, 5, 6, 7, 8, 9,
3, 4, 5, 6, 7, 8, 9,10,
4, 5, 6, 7, 8, 9,10,11,
5, 6, 7, 8, 9,10,11,12,
6, 7, 8, 9,10,11,12,13,
7, 8, 9,10,11,12,13,14 };
methodWhereArrayisPassed(arr);
// do stuff here
}
The name of an array is the address of the first element in it.
Hence the line *state = *arr will set state[0] to arr[0].
Since right now you have defined state as int state[64];, state is const pointer of type int whose address cannot be changed.
You can change it to int *state; and then state = arr will work.
*state = *arr; is using dereferencing, which returns the value at the address of the pointer.
This is the same as state[0] = *arr; because *arr is an int.
See this article for info on pointers. See the deference section.
To solve this problem you want to do this:
for (int i = 0; i < 64; i++) state[i] = arr[i]

array copy reversal in c++

Is there a way to copy an array to another way in reverse order by using a while loop in c++??
I'm pretty sure I know how to do one with a for loop, but I'm curious if anyone knows of a way by using a while loop
Why not something like this?
#include <algorithm>
int src[] = {1, 2, 3, 4, 5};
int dst[5];
std::reverse_copy(src, src+5, dst);
int anArray = {1, 2, 3, 4, 5};
int reverseArray[5];
int count = 4;
int place = 0;
while(place < 5) {
reverseArray[place] = anArray[count];
count--;
place++;
}
As you said that you have done using for loop, you can follow following steps to convert it to while loop.
for(int i = sizeof(arr) - 1; i >= 0; i--)
{
// your logic
}
now convert it to,
int i = sizeof(arr);
for(; i >= 0; )
{
// your logic
i--;
}
simply replace for with while and remove ; within the braces.
int i = sizeof(arr);
while(i >= 0)
{
// your logic
i--;
}
You can use std::reverse for reversing the same array and std::reverse_copy for reversing to another output array as:
int main() {
int a[]= {1,2,3,4,5,6,7,8,9,10};
const int size = sizeof(a)/sizeof(int);
int b[size];
//copying reverse to another array
reverse_copy(a, a + size, b);
cout << "b = {";
copy(b, b + size, ostream_iterator<int>(cout, ", "));
cout << "}" << endl;
//reverse the same array
reverse(a, a + size);
cout << "a = {";
copy(a, a + size, ostream_iterator<int>(cout, ", "));
cout << "}" << endl;
return 0;
}
Output:
b = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1, }
a = {10, 9, 8, 7, 6, 5, 4, 3, 2, 1, }
Demo : http://www.ideone.com/Fe5uj
There's been a few questions similar to this recently. I wonder if it is homework or an interview question somewhere. Here's one answer:
#define ELEMENT_COUNT(a) (sizeof((a))/sizeof((a)[0]))
int anArray[] = { 1, 2, 3, 4, 5 };
int reverseArray[ELEMENT_COUNT(anArray)];
int n = ELEMENT_COUNT(anArray);
int i = 0;
while(n--)
reverseArray[i++] = anArray[n];
I think it might be probing to see if you understand when expression like i++ and n-- are evaluated.