This question already has answers here:
Why aren't variable-length arrays part of the C++ standard?
(10 answers)
Closed 1 year ago.
I was asked to create this function:
int * createAndInput(int & size)
The function initializes an array in the size of
the value size, gets the values from the user as input, and returns the allocated array and the size by ref.
Here is the code I have so far:
int *creatAndInput(int& size)
{
int arr1[***size***];
for (int i = 0; i << size; i++)
{
cout << "enter index " << (i + 1) << endl;
cin >> arr1[i];
}
return (arr1);
}
void main()
{
cout << "enter size number" << endl;
int size2 = 10;
int *size1 = &size2;
cout << *creatAndInput(size2);
}
#include <iostream>
int* createAndInput(int& size)
{
int* ptr = new int[size];
for(int i = 0; i < size; i++){
std::cout << i+1 << ". element: ";
std::cin >> ptr[i];
}
return ptr;
}
int main(){
int *ptr, size;
std::cout << "Size: ";
std::cin >> size;
ptr = createAndInput(size);
for(int i = 0; i < size; i++)
std::cout << i+1 << ". element: "<< ptr[i] << std::endl;
delete[] ptr;
return 0;
}
Related
If I try to run program and ititialize only 2 strings (char*), it works OK. But when I try 3, 4 and more strings initialize, then program just stops. What do I miss?
#include <iostream>
#include <cstring>
template <typename T>
T maxn(T*, int);
template <> char* maxn(char**, int);
template <typename T>
void fill_array(T*, int);
int main()
{
using std::cout;
using std::cin;
int N;
cout << "Input size of array of integers: ";
cin >> N;
int *Arr = new int[N];
fill_array(Arr, N);
cout << "\nMax number in your array is " << maxn(Arr, N) << '\n';
delete [] Arr;
cout << "Input size of array of doubles: ";
cin >> N;
double *ArrDouble = new double[N];
fill_array(ArrDouble, N);
cout << "\nMax number in your array is " << maxn(ArrDouble, N) << '\n';
delete [] ArrDouble;
cout << "Input number of strings, that you plan to input: ";
cin >> N;
cin.get();
char **ArrChar = new char*[N];
for (int i=0; i<N; i++)
{
cout << "Input string #" << i+1 << ": ";
cin.getline(ArrChar[i], 40);
}
cout << "The longest string starts at " << reinterpret_cast<void*>(maxn(ArrChar, N)) << " address";
delete [] ArrChar;
return 0;
}
template <typename T>
void fill_array(T* p_T, int N)
{
for (int i=0; i<N; i++)
{
std::cout << "Enter a number #" << i+1 << ": ";
std::cin >> p_T[i];
}
std::cout << "Array was initializated. Well done!\n";
return;
}
template <typename T>
T maxn(T* p_T, int N)
{
T max=p_T[0];
for (int i=0; i<N-1; i++)
{
if (p_T[i]<p_T[i+1]) max=p_T[i+1];
}
return max;
}
template <> char* maxn(char** str, int N)
{
char* max_len=&str[0][0];
for (int i=0; i<N-1; i++)
{
if (strlen(str[i])<strlen(str[i+1])) max_len=&str[i+1][0];
}
return max_len;
}
I suppose, that problem chains with allocate memory, but don't sure. I tried it with fixwd-size array - program breaks after input first string...
Change this
char **ArrChar = new char*[N];
for (int i=0; i<N; i++)
{
cout << "Input string #" << i+1 << ": ";
cin.getline(ArrChar[i], 40);
}
to this
char **ArrChar = new char*[N];
for (int i=0; i<N; i++)
{
ArrChar[i] = new char[40]; // <-- ADD THIS!
cout << "Input string #" << i+1 << ": ";
cin.getline(ArrChar[i], 40);
}
You need to allocate some memory for your strings, getline won't do that for you.
Having issues with my getPosNums3 function.....all the others work as I need them to. I'm having issues in general understanding pointers, but I am sure that will pass. The aforementioned function spits out the size and address as I need it to, but when I print the newly modified array, it prints out long identical negative integers akin to this: -5476891, -5476891. It'll put out the right amount of integers, which tells me it is a small adjustment that is hanging up my code.....all these functions modify an array down to only its positive values; they just do so via different methods. I appreciate the help
#include <iostream>
using namespace std;
typedef int* IntArrayPtr;
int* getPosNums1(int* arr, int arrSize, int& outPosArrSize);
int* getPosNums2(int* arr, int arrSize, int* outPosArrSizePtr);
void getPosNums3(int* arr, int arrSize, int*& outPosArr, int& outPosArrSize);
void getPosNums4(int* arr, int arrSize, int** outPosArrPtr, int* outPosArrSizePtr);
void printNewArray(int* arr, int arrSize);
void fillArray(int a[], int size);
int main() {
cout << "Fuction 1: " << endl;
int array_size;
cout << "What is the size of the array? ";
cin >> array_size;
IntArrayPtr a;
a = new int[array_size];
fillArray(a, array_size);
int posArraySize;
int* posNums1 = getPosNums1(a, array_size, posArraySize);
cout << "Original array is: ";
printNewArray(a, array_size);
cout << "The new address is " << posNums1 << " and the new size is " << posArraySize << " " << endl;
cout << "New array is: ";
printNewArray(posNums1, posArraySize);
delete[] a;
cout << endl;
cout << "Function 2: " << endl;
int array_size2;
cout << "What is the size of the array? ";
cin >> array_size2;
a = new int[array_size2];
fillArray(a, array_size2);
cout << "Original array is: ";
printNewArray(a, array_size2);
int* posArraySize2 = &array_size2;
int* posNums2 = getPosNums2(a, array_size2, posArraySize2);
cout << "The new address is " << posNums2 << " and the new size is " << *posArraySize2 << " " << endl;
cout << "New array is: ";
printNewArray(posNums2, *posArraySize2);
delete[] a;
cout << endl;
cout << "Function 3: " << endl;
int array_size3;
cout << "What is the size of the array? ";
cin >> array_size3;
a = new int[array_size3];
fillArray(a, array_size3);
cout << "Original array is: ";
printNewArray(a, array_size3);
int* posNums3 = new int[array_size3];
int posArraySize3 = array_size3;
getPosNums3(a, array_size3, posNums3, posArraySize3);
cout << "The new address is " << posNums3 << " and the new size is " << posArraySize3 << endl;
cout << "New array is: ";
printNewArray(posNums3, posArraySize3);
delete[] a;
cout << endl;
cout << "Function 4: " << endl;
int array_size4;
cout << "What is the size of the array? ";
cin >> array_size4;
a = new int[array_size4];
fillArray(a, array_size4);
cout << "Original array is: ";
printNewArray(a, array_size4);
int* posNums4ptr = &array_size4;
int* posNums4 = new int[array_size4];
int** posNums4ptrptr = &posNums4;
getPosNums4(a, array_size4, posNums4ptrptr, posNums4ptr);
cout << "The new address is " << posNums4ptrptr << " and the new size is " << *posNums4ptr << endl;
cout << "New array is: ";
printNewArray(posNums4, *posNums4ptr);
delete[] a;
return 0;
}
int* getPosNums1(int* arr, int arrSize, int& outPosArrSize) {
int* newArray = new int[arrSize];
int counter = 0;
for (int i = 0; i < arrSize; i++) {
if (arr[i] > 0) {
newArray[counter] = arr[i];
counter++;
}
}
outPosArrSize = counter;
return newArray;
}
int* getPosNums2(int* arr, int arrSize, int* outPosArrSizePtr) {
int size = 0, counter = 0;
int newArraySize = 0;
for (int i = 0; i < arrSize; i++) {
if (*(arr + i) > 0) {
newArraySize++;
}
}
int* newArray = new int[newArraySize];
for (int i = 0; i < arrSize; i++) {
if (*(arr + i) > 0) {
newArray[counter] = *(arr + i);
size++;
counter++;
}
}
*outPosArrSizePtr = size;
return newArray;
}
void getPosNums3(int* arr, int arrSize, int*& outPosArr, int& outPosArrSize){
int counter = 0, size = 0;
for (int i = 0; i < arrSize; i++) {
if (*(arr + i) > 0) {
size++;
}
}
int *newArray = new int[size];
for (int i = 0; i < arrSize; i++) {
if (*(arr + i) > 0) {
newArray[counter] = *(arr + i);
counter++;
}
}
delete[] outPosArr;
outPosArr = newArray;
outPosArrSize = size;
delete[] newArray;
newArray = nullptr;
}
void getPosNums4(int* arr, int arrSize, int** outPosArrPtr, int* outPosArrSizePtr){
int size = 0, counter = 0, newArraySize = 0;
for (int i = 0; i < arrSize; i++) {
if (*(arr + i) > 0) {
newArraySize ++;
}
}
int* temp = new int[newArraySize];
for (int i = 0; i < arrSize; i++) {
if (*(arr + i) > 0) {
temp[counter] = arr[i];
size++;
counter++;
}
}
*outPosArrSizePtr = size;
*outPosArrPtr = temp;
}
void printNewArray(int* arr, int arrSize) {
for (int i = 0; i < arrSize; i++)
cout << arr[i] << " ";
cout << endl;
}
void fillArray(int a[], int size) {
cout << "Enter " << size << " integers." << endl;
for (int i = 0; i < size; i++)
cin >> a[i];
}
The code in question is
void getPosNums3(int* arr, int arrSize, int*& outPosArr, int& outPosArrSize){
// [snip] count number of positive entries in arr and call it "size"
int *newArray = new int[size];
// [snip] copy positive entries in arr into newArray
delete[] outPosArr;
outPosArr = newArray;
outPosArrSize = size;
delete[] newArray;
newArray = nullptr;
}
First of all, it's not a good idea for this function to delete[] outPosArr because that presumes that outPosArr is either nullptr or something that was previously allocated with new[]. If it isn't one of those two things then this function has undefined behavior.
Somebody calling a function to copy numbers into an array is not typically going to also want the function to clean up some previous thing that may or may not have been in that array.
But your real problem is that you allocate memory for an array via int *newArray = new int[size], copy stuff in, and then immediately deallocate that memory by calling delete[] newArray. This leaves outPosArr to point to what used to be an array.
Also, assigning nullptr to newArray at the end of the function does nothing, because newArray is going out of scope anyway.
I need to write a C++ program where it swaps between two 1-dimensional
arrays using pointers and functions. Firstly, a void function named showValues to display both arrays before swapping takes and also a void function named swap to swap the elements between both arrays.
My question is: I'm supposed to swap the function but for some reason it wont run and I am not sure where is the error in my code
#include <iostream>
#include <iomanip>
using namespace std;
const int SIZE = 5;
void showValues(int[],int[]);
void swap(int[],int[]);
int main() {
int array1[SIZE] = {10,20,30,40,50};
int array2[SIZE] = {60,70,80,90,100};
showValues (array1, array2);
swap(array1, array2);
return 0;
}
void showValues(int array1[], int array2[]){
cout<<"The original arrays are as shown below: " << endl;
cout << " Array 1 is: ";
for (int i = 0; i < 5; ++i) {
cout << array1[i] << " ";
}
cout << "\n Array 2 is: ";
for (int i = 0; i < 5; ++i) {
cout << array2[i] << " ";
}
}
void swap(int array1[], int array2[])
{
int temp,i;
for(i=0; i<5; ++i)
{
temp = array1[SIZE];
array1[SIZE] = array2[SIZE];
array2[SIZE] = temp;
}
cout << "\nThe swapped arrays are as shown below: " << endl;
cout << " Array 1 is: ";
for (int i = 0; i < 5; ++i) {
cout << array1[i] << " ";
}
cout << "\n Array 2 is: ";
for (int i = 0; i < 5; ++i) {
cout << array2[i] << " ";
}
}
This part of your code doesn't make sense:
temp = array1[SIZE];
array1[SIZE] = array2[SIZE];
array2[SIZE] = temp;
SIZE is 5. So, you are accessing array1[5] and array2[5], i.e. the 6th element of the array. Yet, your arrays have only 5 elements to begin with (array1[0] to array1[4], same for array2), so you are accessing elements beyond the end of the array, which is undefined behavior that is probably just corrupting memory somewhere!
You probably meant to use i here, not SIZE, then the code makes sense. Instead, it would be useful to replace the "magic number" 5 with SIZE:
for(i = 0; i < SIZE; ++i)
{
temp = array1[i];
array1[i] = array2[i];
array2[i] = temp;
}
The void swap(int array1[], int array2[]) function is where you are having trouble. You actually don't even need to have another function for the swapping. You could just use std::swap() which is defined in the #include <utility> header. Since both arrays have the same size.
For example you could do something along these lines:
#include <iostream>
#include <iomanip>
#include <utility>
const int SIZE = 5;
void showValues(int[], int[]);
void swap(int[], int[]);
int main() {
int array1[SIZE] = { 10,20,30,40,50 };
int array2[SIZE] = { 60,70,80,90,100 };
int n = sizeof(array1) / sizeof(array2[0]);
showValues(array1, array2);
std::swap(array1, array2);
std::cout << "\n\nThe swapped arrays are as shown below:\n ";
std::cout << "\nArray 1 is: ";
for (int i = 0; i < n; i++)
std::cout << array1[i] << ", ";
std::cout << "\nArray 2 is: ";
for (int i = 0; i < n; i++)
std::cout << array2[i] << ", ";
return 0;
}
void showValues(int array1[], int array2[]) {
std::cout << "The original arrays are as shown below: " << std::endl;
std::cout << "\nArray 1 is: ";
for (int i = 0; i < 5; ++i) {
std::cout << array1[i] << " ";
}
std::cout << "\nArray 2 is: ";
for (int i = 0; i < 5; ++i) {
std::cout << array2[i] << " ";
}
}
Also consider not using using namespace std;.
In visual studio program crashes: error debug assertion failed. What is wrong in my code? There is no syntax errors. Only warning: deletion of array expression,conversion to pointer suplied When i run it with cmd standart compiler it works fine.
#include "stdafx.h"
#include <stdio.h>
#include <iostream>
using namespace std;
#define max_size 100
class my_array{
int* arr[max_size];
public:
my_array() {}
my_array(int size) {
if (size <= 0 || size > max_size) {
exit(1);
}
for (int i = 0; i < size; i++) {
arr[i] = new int;
cout << "Enter element [" << i + 1 << "] = ";
cin >> *arr[i];
}
}
~my_array() {
delete[] arr;
}
void operator[](int n) {
cout << endl;
for (int i = 0; i < n; i++) {
cout << "Enter element [" << i << "] = " << *arr[i] << endl;
}
}
};
int main() {
my_array array(6);
array[5];
return 0;
}
You are deleting arr here:
delete[] arr;
while arr has never been allocated by new. In your original program arr is a fixed size array of pointers to int.
You probably want this:
class my_array {
int *arr;
public:
my_array() {}
my_array(int size) {
if (size <= 0 || size > max_size) { // BTW this test isn't really necessary, as we
// can allocate as much memory as available
// anyway much more than just 100
exit(1);
}
arr = new int[size]; // allocate array of size size
for (int i = 0; i < size; i++) {
cout << "Enter element [" << i + 1 << "] = ";
cin >> arr[i];
}
}
~my_array() {
delete[] arr; // delete array allocated previously
}
void operator[](int n) {
cout << endl;
for (int i = 0; i < n; i++) {
cout << "Enter element [" << i << "] = " << arr[i] << endl;
}
}
};
Instead of having a fixed size array of pointers to int, you have a dynamic array of ints.
There is still room for improvement though. For example the my_array() constructor is pointless here, And it's odd to use the [] operator for printing the content, and the text "Enter element [" in the [] operator is also questionable.
I am Having Problem with Passing a 2D array to a c++ Function. The function is supposed to print the value of 2D array. But getting errors.
In function void showAttributeUsage(int)
Invalid types for int(int) for array subscript.
I know the problem is with the syntax in which I am passing the particular array to function but I don't know how to have this particular problem solved.
Code:
#include <iostream>
using namespace std;
void showAttributeUsage(int);
int main()
{
int qN, aN;
cout << "Enter Number of Queries : ";
cin >> qN;
cout << "\nEnter Number of Attributes : ";
cin >> aN;
int attVal[qN][aN];
cout << "\nEnter Attribute Usage Values" << endl;
for(int n = 0; n < qN; n++) { //for looping in queries
cout << "\n\n***************** COLUMN " << n + 1 << " *******************\n\n";
for(int i = 0; i < aN; i++) { //for looping in Attributes
LOOP1:
cout << "Use(Q" << n + 1 << " , " << "A" << i + 1 << ") = ";
cin >> attVal[n][i];
cout << endl;
if((attVal[n][i] > 1) || (attVal[n][i] < 0)) {
cout << "\n\nTHE VALUE MUST BE 1 or 0 . Please Re-Enter The Values\n\n";
goto LOOP1; //if wrong input value
}
}
}
showAttributeUsage(attVal[qN][aN]);
cout << "\n\nYOUR ATTRIBUTE USAGE MATRIX IS\n\n";
getch();
return 0;
}
void showAttributeUsage(int att)
{
int n = 0, i = 0;
while(n != '\0') {
while(i != '\0') {
cout << att[n][i] << " ";
i++;
}
cout << endl;
n++;
}
}
I really suggest to use std::vector : live example
void showAttributeUsage(const std::vector<std::vector<int>>& att)
{
for (std::size_t n = 0; n != att.size(); ++n) {
for (std::size_t i = 0; i != att.size(); ++i) {
cout << att[n][i] << " ";
}
cout << endl;
}
}
And call it that way:
showAttributeUsage(attVal);
Looking at your code, I see no reason why you can't use std::vector.
First, your code uses a non-standard C++ extension, namely Variable Length Arrays (VLA). If your goal is to write standard C++ code, what you wrote is not valid standard C++.
Second, your initial attempt of passing an int is wrong, but if you were to use vector, your attempt at passing an int will look almost identical if you used vector.
#include <iostream>
#include <vector>
#include <algorithm>
#include <iterator>
typedef std::vector<int> IntArray;
typedef std::vector<IntArray> IntArray2D;
using namespace std;
void showAttributeUsage(const IntArray2D&);
int main()
{
int qN, aN;
cout << "Enter Number of Queries : ";
cin >> qN;
cout << "\nEnter Number of Attributes : ";
cin >> aN;
IntArray2D attVal(qN, IntArray(aN));
//... Input left out ...
showAttributeUsage(attVal);
return 0;
}
void showAttributeUsage(const IntArray2D& att)
{
for_each(att.begin(), att.end(),
[](const IntArray& ia) {std::copy(ia.begin(), ia.end(), ostream_iterator<int>(cout, " ")); cout << endl;});
}
I left out the input part of the code. The vector uses [] just like a regular array, so no code has to be rewritten once you declare the vector. You can use the code given to you in the other answer by molbdnilo for inputing the data (without using the goto).
Second, just to throw it into the mix, the showAttributeUsage function uses the copy algorithm to output the information. The for_each goes throw each row of the vector, calling std::copy for the row of elements. If you are using a C++11 compliant compiler, the above should compile.
You should declare the function like this.
void array_function(int m, int n, float a[m][n])
{
for (int i = 0; i < m; i++)
for (int j = 0; j < n; j++)
a[i][j] = 0.0;
}
where you pass in the dimensions of array.
This question has already been answered here. You need to use pointers or templates. Other solutions exists too.
In short do something like this:
template <size_t rows, size_t cols>
void showAttributeUsage(int (&array)[rows][cols])
{
for (size_t i = 0; i < rows; ++i)
{
std::cout << i << ": ";
for (size_t j = 0; j < cols; ++j)
std::cout << array[i][j] << '\t';
std::cout << std::endl;
}
}
You're using a compiler extension that lets you declare arrays with a size determined at runtime.
There is no way to pass a 2D array with such dimensions to a function, since all but one dimension for an array as a function parameter must be known at compile time.
You can use fixed dimensions and use the values read as limits that you pass to the function:
const int max_queries = 100;
const int max_attributes = 100;
void showAttributeUsage(int array[max_queries][max_attributes], int queries, int attributes);
int main()
{
int attVal[max_queries][max_attributes];
int qN = 0;
int aN = 0;
cout << "Enter Number of Queries (<= 100) : ";
cin >> qN;
cout << "\nEnter Number of Attributes (<= 100) : ";
cin >> aN;
cout << "\nEnter Attribute Usage Values" << endl;
for (int n = 0; n < qN; n++)
{
cout << "\n\n***************** COLUMN " << n + 1 <<" *******************\n\n";
for (int i = 0; i < aN; i++)
{
bool bad_input = true;
while (bad_input)
{
bad_input = false; // Assume that input will be correct this time.
cout << "Use(Q" << n + 1 << " , " << "A" << i + 1 << ") = ";
cin >> attVal[n][i];
cout << endl;
if (attVal[n][i] > 1 || attVal[n][i] < 0)
{
cout << "\n\nTHE VALUE MUST BE 1 or 0 . Please Re-Enter The Values\n\n";
bad_input = true;
}
}
}
}
cout << "\n\nYOUR ATTRIBUTE USAGE MATRIX IS\n\n";
showAttributeUsage(attVal, qN, aN);
getch();
return 0;
}
void showAttributeUsage(int att[max_queries][max_attributes], int queries, int attributes)
{
for (int i = 0; i < queries; i++)
{
for (int j = 0; j < attributes; j++)
{
cout << att[i][j] << " ";
}
cout << endl;
}
}
For comparison, the same program using std::vector, which is almost identical but with no size limitations:
void showAttributeUsage(vector<vector<int> > att);
int main()
{
cout << "Enter Number of Queries (<= 100) : ";
cin >> qN;
cout << "\nEnter Number of Attributes (<= 100) : ";
cin >> aN;
vector<vector<int> > attVal(qN, vector<int>(aN));
cout << "\nEnter Attribute Usage Values"<<endl;
for (int n = 0; n < qN; n++)
{
cout<<"\n\n***************** COLUMN "<<n+1<<" *******************\n\n";
for (int i = 0; i < aN; i++)
{
bool bad = true;
while (bad)
{
bad = false;
cout << "Use(Q" << n + 1 << " , " << "A" << i + 1 << ") = ";
cin >> attVal[n][i];
cout << endl;
if (attVal[n][i] > 1 || attVal[n][i] < 0)
{
cout << "\n\nTHE VALUE MUST BE 1 or 0 . Please Re-Enter The Values\n\n";
bad = true;
}
}
}
}
cout << "\n\nYOUR ATTRIBUTE USAGE MATRIX IS\n\n";
showAttributeUsage(attVal);
getch();
return 0;
}
void showAttributeUsage(vector<vector<int> > att);
{
for (int i = 0; i < att.size(); i++)
{
for (int j = 0; j < att[i].size(); j++)
{
cout << att[i][j] << " ";
}
cout << endl;
}
}
The Particular Logic worked for me. At last found it. :-)
int** create2dArray(int rows, int cols) {
int** array = new int*[rows];
for (int row=0; row<rows; row++) {
array[row] = new int[cols];
}
return array;
}
void delete2dArray(int **ar, int rows, int cols) {
for (int row=0; row<rows; row++) {
delete [] ar[row];
}
delete [] ar;
}
void loadDefault(int **ar, int rows, int cols) {
int a = 0;
for (int row=0; row<rows; row++) {
for (int col=0; col<cols; col++) {
ar[row][col] = a++;
}
}
}
void print(int **ar, int rows, int cols) {
for (int row=0; row<rows; row++) {
for (int col=0; col<cols; col++) {
cout << " | " << ar[row][col];
}
cout << " | " << endl;
}
}
int main () {
int rows = 0;
int cols = 0;
cout<<"ENTER NUMBER OF ROWS:\t";cin>>rows;
cout<<"\nENTER NUMBER OF COLUMNS:\t";cin>>cols;
cout<<"\n\n";
int** a = create2dArray(rows, cols);
loadDefault(a, rows, cols);
print(a, rows, cols);
delete2dArray(a, rows, cols);
getch();
return 0;
}
if its c++ then you can use a templete that would work with any number of dimensions
template<typename T>
void func(T& v)
{
// code here
}
int main()
{
int arr[][7] = {
{1,2,3,4,5,6,7},
{1,2,3,4,5,6,7}
};
func(arr);
char triplestring[][2][5] = {
{
"str1",
"str2"
},
{
"str3",
"str4"
}
};
func(triplestring);
return 0;
}