My question is as follows:
Refer to the following array declaration in the main():
const int size = 4;
int x[size][size] = {{1, 2, 3, 4}, {5, 6, 7, 8},
{9, 8, 7, 3}, {2, 1, 7, 1}};
Write a function SwapRows() to swap two rows of the above 2D array. For
example, if the function has been called to swap the first and the second rows of the
above 2D array then the result would be that the first row now becomes {5, 6, 7, 8}
and the second row now becomes {1, 2, 3, 4}. The function receives as parameter the
2D array, the size of the array, and two integers to indicate the rows to swap.
Help,,how can i go about this?????
Note: Using C++ Language
Pseudo code:
SwapRows(x[size][size], row0, row1, size)
for col = 0 to size - 1 do
temp = x[row0][col]
x[row0][col] = x[row1][col]
x[row1][col] = temp
Now all you need to do is convert the pseudo code into C++, then test, debug and document it.
#include <algorithm>
void SwapRows(int arr[][4], int r1, int r2)
{
std::swap(arr[r1],arr[r2]);
}
Related
Recently while going over C++, I dynamically allocated space for an array and tried to initialize it with 8 default values on the next line.
int* intArray = new int[8];
intArray = {1, 2, 3, 4, 5, 6, 7, 8};
Visual Studio didn't like that, and underlined the 2 in red, as if there is a problem there, only to give me the error "too many initializer values"
I don't know if I used incorrect syntax or if you're just not allowed to set the value of an array that way after declaration. Any ideas?
Okay, it seems this also isn't working for regular non-pointer arrays too, I must be just doing something dumb.
intArray is not an array, it's a pointer. A pointer can't be initialized with an initializer list.
Dynamic allocated memory can be initialized at the moment of allocation:
int* intArray = new int[8] {1, 2, 3, 4, 5, 6, 7, 8};
C array can be initialized also at the declaration:
int intArray[8] = {1, 2, 3, 4, 5, 6, 7, 8};
C++ allows static allocation without dimension parameter
int intArray[] = {1, 2, 3, 4, 5, 6, 7, 8};
where for dynamic allocation
int *intArray = new int[8] {1, 2, 3, 4, 5, 6, 7, 8};
the matching dimension must be passed.
Here is an example of what I am trying to do:
int size = 10;
int *data = new int[size];
int *array_1 = &data[0];
int *array_2 = &data[size/2];
//fill array_1 and array_2 with data
sort(array_1, array_1+size/2);
sort(array_2, array_2+size/2);
//now, is it possible to merge the 2 sorted arrays?
For example if array_1 = {1, 4, 7} and array_2 = {3, 5, 6}
I am trying to make data = {1, 3, 4, 5, 6, 7}
You want std::inplace_merge. See http://www.cplusplus.com/reference/algorithm/inplace_merge/
So I have a pointer to a 2D array like so:
int board[3][5] = { 3, 5, 2, 2, 1, 3, 4, 34, 2, 2, 3, 4, 3, 223, 923 };
int* ptr[sizeof(board[0]) / sizeof(board[0][0])] = board;
I'm trying to follow this example. But for some reason I'm getting the error:
IntelliSense: initialization with '{...}' expected for aggregate
object
Any idea what the problem is?
Assign pointer to the first element of the array like below
int (*ptr)[5] = board;
Note: Column size [5] in the pointer declaration should be equal to the original 2 dimension array column size [5].
Declaring row size [3] is optional.
int main() {
int board[3][5] = { 3, 5, 2, 2, 1, 3, 4, 34, 2, 2, 3, 4, 3, 223, 923 };
/*
// 3 Rows 5 Columns Matrix
int board[3][5] = { {3, 5, 2, 2, 1 },
{3, 4, 34, 2, 2 },
{3, 4, 3, 223, 923}
};
*/
// Assign pointer to the first element of the array
int (*ptr)[5] = board;
for(int i=0; i< (3*5); i++) {
std::cout<<(*ptr)[i]<<std::endl;
}
return 0;
}
A 2D array is not the same as an array of pointers. You cannot directly convert one to the other.
I just needed to put () around the *ptr. I have no idea how this fixes it but now I can do ptr[1][2].
So I want to initialize an int 2d array very quickly, but I can't figure out how to do it. I've done a few searches and none of them say how to initialize a 2D array, except to do:
int [SOME_CONSTANT][ANOTHER_CONSTANT] = {{0}};
Basically, I've got 8 vertices, and I'm listing the 4 vertices of each face of a cube in an array. I've tried this:
int[6][4] sides = {{0, 1, 2, 3}, {4, 5, 6, 7}, {0, 4, 7, 3}, {7, 6, 2, 3}, {5, 1, 2, 6}, {0, 1, 5, 4}};
But that tells me that there's an error with 'sides', and that it expected a semi-colon. Is there any way to initialize an array quickly like this?
Thanks!
You have the [][] on the wrong side. Try this:
int sides[6][4] = {{0, 1, 2, 3}, {4, 5, 6, 7}, {0, 4, 7, 3}, {7, 6, 2, 3}, {5, 1, 2, 6}, {0, 1, 5, 4}};
Keep in mind that what you really have is:
int **sides
(A pointer to a pointer of ints). It's sides that has the dimensions, not the int. Therefore, you could also do:
int x, y[2], z[3][4], ...;
I think You meant to say
int sides[6][4] = {{0, 1, 2, 3}, {4, 5, 6, 7}, {0, 4, 7, 3}, {7, 6, 2, 3}, {5, 1, 2, 6}, {0, 1, 5, 4}};
int array[n][m] behaves just like int array[n * m].
In fact, array[i][j] = array[m * i + j] for all i, j.
So int array[2][3] = {1, 2, 3, 4, 5, 6}; is a valid declaration and, for example,
array[1][1] = array[3 * 1 + 1] = array[4] = 5.
int sides[6][4] = {{0, 1, 2, 3}, {4, 5, 6, 7}, {0, 4, 7, 3}, {7, 6, 2, 3}, {5, 1, 2, 6}, {0, 1, 5, 4}};
I'm not a regular c++ programmer but I looks like int sides[6][4] seems to compile while int[6][4] sides fails. Languages like C# lets you have the [][] on either sides but apparently c++ doesn't.
int sides[6][4] = ... should do the trick. This sounds like you may be coming from a Java (or other language) background so I do recommend a C++ book The Definitive C++ Book Guide and List for more details.
Yes, the intended type of sides is int[6][4], but C++ has confusing syntax sometimes. The way to declare said array is:
int sides[6][4] = {/*stuff*/};
You run into this with function pointers too, but even worse:
int (*myfuncptr)(int); //creates a function pointer called myfuncptr
With function pointers though, you can do this:
typedef int (*func_ptr_type)(int);
func_ptr_type myfuncptr;
Unfortunately, there's no corresponding magic trick for arrays.
i would make a array outside of function and just assign it it to your local. this will very likely invoke memcpy or just inline memory copying loop
this is the fastest you can get
How to initialize a 2 dimensional vector<int> in C++?
For instance I have 4 arrays each of length 8 ints, like the below
int a1[] = {1,2,3,4,5,6,7,8};
int a2[] = {1,2,3,4,9,10,11,12};
int a3[] = {1,2,5,6,9,10,13,14};
int a4[] = {1,3,5,7,9,11,13,15};
and I have this
vector< vector <int> > aa (4);
aa[i] (a1,a1+8);
But this gives error. I even tried supplying the array a1 to v1 and passed v1 to aa[i] , still it fails.
So what would be the proper way of initializing the elements of a 2 dimensional vector<int>
aa[i].assign(a1,a1+8);
int arr[4][8] =
{
{1, 2, 3, 4, 5, 6, 7, 8},
{1, 2, 3, 4, 9, 10, 11, 12},
{1, 2, 5, 6, 9, 10, 13, 14},
{1, 3, 5, 7, 9, 11, 13, 15},
};
std::vector<std::vector<int> > vec(4, std::vector<int>(8));
for (int i = 0; i < 4; ++i)
{
vec[i].assign(arr[i], arr[i] + 8);
}
The initialization of aa also initialized all four of the contained vector<int> objects, using the default constructor for vector<int>. So you'll need to add data to those empty vectors, not initialize them.
Try for example:
std::copy(a1, a1+8, std::back_inserter(aa[i]));