I am a student who is doing an assignment for C++ and I have encountered something I am very unfamiliar with. I have an int array with no size but a list of numbers. After it's creation, there is a function call inside a function that has that array as a parameter with an index in it.
For example:
for (int x = 0; x < CAPACITY, x++)
functionCall(array[x]);
Now I am supposed to create a function so the call can work. However when I make my function:
void functionCall(int array[]);
It does not work because it cannot turn an int to an int[].
I guess my question is, how am I supposed to get that list of numbers created originally by the array if I have to call it in my function as if it isn't an array.
Right now if I just put as an int but not an array like it wants me to do it just gives me the number 5 but not any of the numbers in the array. For example:
void functionCall(int array);
Sincere thank you for anything and I apologize if this sounds confusing.
functionCall(array[x]);
This passes the xth element in the array to the function, so a single int.
array[2] = 5;
functionCall(array[2]); // This is the same as functionCall(5);
So in the function, you get the current element of the array. Not the array itself.
You cannot get the list inside the function, because you only give a single element of that list each time you call it.
Taking a wild guess, I suspect you are looking for something like the MCVE below:
#include <iostream>
void functionCall(int v) {
std::cout << v << " ";
}
void func(int array[], size_t CAPACITY) {
for (size_t x = 0; x < CAPACITY; x++)
functionCall(array[x]);
}
int main() {
int list[] = { 1,2,3,4,3,0, 42 };
func(list, std::distance(std::begin(list), std::end(list)));
return 0;
}
Related
I am working on a project which requires certain actions be in their own functions. Right now, I must take the random values generated, and output them FROM an array. I have the values stored in numarray , but I don't know how I can call that array in the function to output the values. I have a function set up which seems like it will take the array and output it, but I don't know how to call the function without an argument to pass through it in main. Is this a possible way to output the array, or is there a completely different way this should be done.
PS: I know namespace isn't good, but it's what I have to do to pass the class.
#include <iostream>
#include <fstream>
#include <time.h>
#include <stdlib.h>
#include <cstddef>
using namespace std;
ofstream randomData;
ifstream inputrandomData;
void randomgenerator();
void read();
void printArray(int *numarray);
void randomgenerator() {
srand(time(0));
randomData.open("randomData.txt");
for (int counter = 0; counter < 100; counter++) {
randomData << rand() % 100+1 << endl;
}
randomData.close();
}
void read() {
inputrandomData.open("randomData.txt");
int numarray[100] = {};
for (int i = 0; i < 100; i++) {
inputrandomData >> numarray[i];
}
inputrandomData.close();
}
void printArray(int *numarray) {
for (int index = 0; index < 100; index++) {
cout << numarray[index];
}
}
int main() {
randomgenerator();
read();
printArray();
return 0;
}
The randomgenerator function is what makes the values and stores them in a file.
The read function takes those values and stores them in an array.
printarray is the function where I want to output the array values, and is giving me the problem.
You need to dynamically allocate and return numarray from read. Or even better create numarray like you did here on the stack, but do it in main and pass it as an argument to read, then pass as an argument to printArray.
As it is numarray will go out of scope when read completes, since your allocating it on the stack.
Solution (as per your code): Declare the local array variable in main. Passby pointer to function along with array size as it required to process array inside a passed function. This kind of design is not preferable.
You can design the class as there are some data members involved, on which you can call the method of that class.
You can prefer the std::vector as data member to hold data with a reserve the size as per yours requirement. Because the reserve method of std::vector avoid reallocation as vector size grow. Here, you have size 100. So you can reserve the 100 items of std::vector.
(I'm a student and this is my first time posting so go easy on me.)
I want to create a function that takes a 2D array as an argument and in that array, I'd like to have a variable that I want to modify later in the code. This is the closest thing to an example of what I want:
int size; //the variable I want to change later
void function(int[][size]);
int main(){
cin >> size;
int array[size][size]; //the array I'm using with the variable as a parameter
function(array)
}
void function(int array[][size]){
//Do thing....
}
The code above does give me an error (array bound is not an integer constant) so if I make the variable a constant it will compile as seen here:
const int size = 10;
void function(int[][size]);
int main(){
int array[size][size];
function(array)
}
void function(int array[][size]){
//Do thing....
}
This does compile like I said, but now I can't modify the variable and need to declare its value in the code beforehand. I assume that the variable needs to be global so that I can use it in the function, and with that said, I can't get pointers to work either most likely because it's a global variable and not a local one. Here's an example of something I tried, but got an error (invalid conversion from ‘const int*’ to ‘int*’):
const int size = 10;
void function(int[][size]);
int main(){
int *other = &size;
*other = 5;
}
Any help would be appreciated, thanks.
Plain ol' arrays aren't resizeable in C++. Even more frustrating, their size has to be a constant - you can't make the size a variable that gets set at runtime. Ever more frustrating, the size you put in an array that's a function parameter is a constraint, and it's not even enforced. It's just decor.
As it was hinted in the comments, std::vector<TYPE> is the go-to "resizeable array" in C++. You can create a vector like this:
#include <vector>
int main() {
std::vector<int> my_int_array;
}
And you can resize it like this:
int new_size = 42;
my_int_array.resize(new_size);
And you can pass it to a function by reference(see the &) so that changes to myint_array inside the function affect it outside the function.
void my_awesome_function(std::vector<int>& int_array);
my_awesome_function(my_int_array);
So let's say you have a 2D matrix, implemented as a vector of vectors:
std::vector<std::vector<int>> matrix = { { 1,2,3 }, { 4,5,6 } }
If you want to change the number of columns, you have to resize each row array:
int new_column_count = 10;
for (auto& row : matrix) {
row.resize(new_column_count );
}
You can pass around matrix by reference (e.g. std::vector<std::vector<int>>&) and resize it when you need to.
I am trying to return an array Data Member from one smaller 2D Array Object, and trying to insert the array into a larger 2D array object. But when attempting this, I came into two problems.
First problem is that I want to return the name of the 2D array, but I do not know how to properly syntax to return 2D Array name.
This is what my 2D Array data member looks like
private:
int pieceArray[4][4];
// 2D Smaller Array
and I want to return this array into a function, but this one causes a compiler error:
int Piece::returnPiece()
{
return pieceArray; //not vaild
// return the 2D array name
}
I tired using this return type and it worked:
int Piece::returnPiece()
{
return pieceArray[4][4];
}
But I am unsure if this is what I want, as I want to return the array and all of it's content.
The other problem is the InsertArray() function, where I would put the returnPiece() function in the InsertArray()'s argument.
The problem with the InsertArray() is the argument, heres the code for it:
void Grid::InsertArray( int arr[4][4] ) //Compiler accepts, but does not work
{
for(int i = 0; i < x_ROWS ; ++i)
{
for (int j = 0; j < y_COLUMNS ; ++j)
{
squares[i][j] = arr[i][j];
}
}
}
The problem with this is that it does not accept my returnPiece(), and if i remove the "[4][4]", my compiler does not accept.
Mostly all these are syntax errors, but how do I solve these problems?
Returning the whole pieceArray in returnPiece()
The correct syntax for the argument in InsertArray()
The argument of InsertArray() accepting the returnPiece()
These 3 are the major problems that I need help with, and had the same problem when I attempt to use the pointer pointer method. Does anyone know how to solve these 3 problems?
When passing your array around, you have to decide whether or not you want to make a copy of the array, or if you just want to return a pointer to the array. For returning arrays, you can't (easily) return a copy - you can only return a pointer (or reference in C++). For example:
// Piece::returnPiece is a function taking no arguments and returning a pointer to a
// 4x4 array of integers
int (*Piece::returnPiece(void))[4][4]
{
// return pointer to the array
return &pieceArray;
}
To use it, call it like so:
int (*arrayPtr)[4][4] = myPiece->returnPiece();
int cell = (*arrayPtr)[i][j]; // cell now stores the contents of the (i,j)th element
Note the similarity between the type declaration and using it - the parentheses, dereferencing operator *, and brackets are in the same places.
Your declaration for Grid::InsertArray is correct - it takes one argument, which is a 4x4 array of integers. This is call-by-value: whenever you call it, you make a copy of your 4x4 array, so any modification you make are not reflected in the array passed in. If you instead wanted to use call-by-reference, you could pass a pointer to an array instead:
// InsertArray takes one argument which is a pointer to a 4x4 array of integers
void Grid::InsertArray(int (*arr)[4][4])
{
for(int i = 0; i < x_ROWS; i++)
{
for(int j = 0; j < y_COLUMNS ; j++)
squares[i][j] = (*arr)[i][j];
}
}
These type declarations with pointers to multidimensional arrays can get really confusing fast. I recommend making a typedef for it like so:
// Declare IntArray4x4Ptr to be a pointer to a 4x4 array of ints
typedef int (*IntArray4x4Ptr)[4][4];
Then you can declare your functions much more readable:
IntArray4x4Ptr Piece::returnPiece(void) { ... }
void Grid::InsertArray(IntArray4x4Ptr arr) { ... }
You can also use the cdecl program to help decipher complicated C/C++ types.
It seems like you need to read up more on pointers in C++ and on pass by reference vs. pass by value.
Your returnPiece method is defined as returning the value of a single cell. Given the index (e.g., [4][4]) you return a copy of the contents of that cell, so you won't be able to change it, or more correctly, changing it would change the copy.
I'm sure someone will give you the correct syntax, but I would really recommend learning this stuff since otherwise you may use the code that you do get incorrectly.
Here is how I would do it:
class Array {
public:
Array() {
for (int i = 0; i < 4; ++i)
{
for (int j = 0; j < 4; ++j)
{
(*this)(i, j) = 0;
}
}
}
int &operator()(int i, int j)
{
return pieceArray[i][j];
}
private:
int pieceArray[4][4];
};
You can then do something like:
Array x; // create 4x4 array
x(1, 2) = 3; // modify element
Trouble with Adam Rosenfield's arrayPtr in that Piece::pieceArray can change out from under you. (Copy-by-reference vs Copy-by-value.)
Copy-by-value is inefficient. But if you really want to do it, just cheat:
struct FOO { int piece [4][4]; };
FOO Piece::returnPiece()
{
FOO f;
memcpy( f.piece, pieceArray, sizeof(pieceArray) );
return f;
}
void Grid::InsertArray( const FOO & theFoo )
{
// use theFoo.piece[i][j]
}
Of course, a better, more Object-Oriented solution, would be to have returnPiece() create and return a Piece or Array object. (As Juan suggested...)
I need to pass different array of structures to function, but I don't know how to do it. Each time, I'm getting an error. I go through the Internet but all examples I found are about passing specific or only one array of structure to function (Passing array of structures to function c++) but what if I have different structures each time and I want to pass it to the same function.
So I'm not sure if what I want to do is applicable or not.
To clarify more if I have the following structures:
struct EVRL_Mapping2 {
double avgMap2;
int permutationMap2[2];
};
struct EVRL_Mapping3 {
double avgMap3;
int permutationMap3[3];
};
struct EVRL_Mapping4 {
double avgMap4;
int permutationMap4[4];
};
EVRL_Mapping2 EVRL_Map2[2]; //Mapping2: AC3,AC2 (2 mapping)
EVRL_Mapping3 EVRL_Map3[2]; //Mapping3: AC3,AC2,AC1 (2 mapping)
EVRL_Mapping4 EVRL_Map4[1]; //Mapping4: AC3,AC2,AC1,AC0 (1 mapping)
Now in the .CC code, if I have an array of two elements of EVRL_Mapping2 (EVRL_Map2[2]) and I want to find the maximum of avgMap2 between the two elements of structure and return the index/location of that element. Is it going to be like this:
if yes, does it mean for each structure I need to define a separate function!?
int findMax(struct EVRL_Mapping2 myarray[], int size){
for(int i=0;i<size;i++){
// printf("myarray[%d]=%d\n",i,myarray[i]);
}
double max = myarray[0].avgMap2;
int index = 0;
for(int i = 1; i<size; i++)
{
if(myarray[i] > max){
max = myarray[i].avgMap2;
index = i;
printf("Inside if(): index=%d\n",index);
}
}
return index;
printf("Inside findMax(): index=%d\n",index);
}
Now calling and passing to this function:
findMax(EVRL_Map2,2);
However, I have an error with the above function definition and the code doesn't compile.So can you advise?
Thanks for your help in advance.
I am trying to return an array Data Member from one smaller 2D Array Object, and trying to insert the array into a larger 2D array object. But when attempting this, I came into two problems.
First problem is that I want to return the name of the 2D array, but I do not know how to properly syntax to return 2D Array name.
This is what my 2D Array data member looks like
private:
int pieceArray[4][4];
// 2D Smaller Array
and I want to return this array into a function, but this one causes a compiler error:
int Piece::returnPiece()
{
return pieceArray; //not vaild
// return the 2D array name
}
I tired using this return type and it worked:
int Piece::returnPiece()
{
return pieceArray[4][4];
}
But I am unsure if this is what I want, as I want to return the array and all of it's content.
The other problem is the InsertArray() function, where I would put the returnPiece() function in the InsertArray()'s argument.
The problem with the InsertArray() is the argument, heres the code for it:
void Grid::InsertArray( int arr[4][4] ) //Compiler accepts, but does not work
{
for(int i = 0; i < x_ROWS ; ++i)
{
for (int j = 0; j < y_COLUMNS ; ++j)
{
squares[i][j] = arr[i][j];
}
}
}
The problem with this is that it does not accept my returnPiece(), and if i remove the "[4][4]", my compiler does not accept.
Mostly all these are syntax errors, but how do I solve these problems?
Returning the whole pieceArray in returnPiece()
The correct syntax for the argument in InsertArray()
The argument of InsertArray() accepting the returnPiece()
These 3 are the major problems that I need help with, and had the same problem when I attempt to use the pointer pointer method. Does anyone know how to solve these 3 problems?
When passing your array around, you have to decide whether or not you want to make a copy of the array, or if you just want to return a pointer to the array. For returning arrays, you can't (easily) return a copy - you can only return a pointer (or reference in C++). For example:
// Piece::returnPiece is a function taking no arguments and returning a pointer to a
// 4x4 array of integers
int (*Piece::returnPiece(void))[4][4]
{
// return pointer to the array
return &pieceArray;
}
To use it, call it like so:
int (*arrayPtr)[4][4] = myPiece->returnPiece();
int cell = (*arrayPtr)[i][j]; // cell now stores the contents of the (i,j)th element
Note the similarity between the type declaration and using it - the parentheses, dereferencing operator *, and brackets are in the same places.
Your declaration for Grid::InsertArray is correct - it takes one argument, which is a 4x4 array of integers. This is call-by-value: whenever you call it, you make a copy of your 4x4 array, so any modification you make are not reflected in the array passed in. If you instead wanted to use call-by-reference, you could pass a pointer to an array instead:
// InsertArray takes one argument which is a pointer to a 4x4 array of integers
void Grid::InsertArray(int (*arr)[4][4])
{
for(int i = 0; i < x_ROWS; i++)
{
for(int j = 0; j < y_COLUMNS ; j++)
squares[i][j] = (*arr)[i][j];
}
}
These type declarations with pointers to multidimensional arrays can get really confusing fast. I recommend making a typedef for it like so:
// Declare IntArray4x4Ptr to be a pointer to a 4x4 array of ints
typedef int (*IntArray4x4Ptr)[4][4];
Then you can declare your functions much more readable:
IntArray4x4Ptr Piece::returnPiece(void) { ... }
void Grid::InsertArray(IntArray4x4Ptr arr) { ... }
You can also use the cdecl program to help decipher complicated C/C++ types.
It seems like you need to read up more on pointers in C++ and on pass by reference vs. pass by value.
Your returnPiece method is defined as returning the value of a single cell. Given the index (e.g., [4][4]) you return a copy of the contents of that cell, so you won't be able to change it, or more correctly, changing it would change the copy.
I'm sure someone will give you the correct syntax, but I would really recommend learning this stuff since otherwise you may use the code that you do get incorrectly.
Here is how I would do it:
class Array {
public:
Array() {
for (int i = 0; i < 4; ++i)
{
for (int j = 0; j < 4; ++j)
{
(*this)(i, j) = 0;
}
}
}
int &operator()(int i, int j)
{
return pieceArray[i][j];
}
private:
int pieceArray[4][4];
};
You can then do something like:
Array x; // create 4x4 array
x(1, 2) = 3; // modify element
Trouble with Adam Rosenfield's arrayPtr in that Piece::pieceArray can change out from under you. (Copy-by-reference vs Copy-by-value.)
Copy-by-value is inefficient. But if you really want to do it, just cheat:
struct FOO { int piece [4][4]; };
FOO Piece::returnPiece()
{
FOO f;
memcpy( f.piece, pieceArray, sizeof(pieceArray) );
return f;
}
void Grid::InsertArray( const FOO & theFoo )
{
// use theFoo.piece[i][j]
}
Of course, a better, more Object-Oriented solution, would be to have returnPiece() create and return a Piece or Array object. (As Juan suggested...)