I'm not sure what to call this, so I'm also not sure what to search for, but is there a way to use 'i' as part of a variable name within a for loop? Using C++ by the way.
For example,
int int1, int2, int3;
for(int i = 1; i<=3; i++){
//somehow use i as inti or int+i, etc.
//I was wondering if this is possible?
}
I appreciate any input.
Thanks.
use an array
int ints [3];
for(int i = 0; i<3; i++){
int x = ints[i];
}
Department for insane solutions:
int int1, int2, int3;
int *arr[3] = { &int1, &int2, &int3 };
for(int i = 1; i<=3; i++){
... *arr[i] ...
}
would also work, but not as easy as using an array, of course.
If you are using C++ you should pick up one of the containers from the C++ standard library, as [std::array]1 or [std::vector]2.
Example:
#include <array>
#include <iostream>
int main() {
std::array<int, 3> const ia = {{ 2, 4, 8 }};
for( int i : ia ) {
std::cout << "[" << i << "] ";
}
std::cout << std::endl;
return 0;
}
Related
#include <iostream>
#include <vector>
int i=0; //points at the current stack that we are working with
int box=0; //no. of boxes held by the crane
int64_t H; //max. height of the stacks given in the que.
int main()
{
int n, value; //storing no. of stacks and creating an additional variable value to store operations
std::cin>> n >> H;
int64_t arr[n]; //storing the no. of boxes each stack has in an array
std::vector<int> arr2; //storing the operations we have to perform in a vector
for(int j=0; j<n; j++){std::cin>> arr[j];} //getting arr
while(std::cin>>value) //getting arr2
{
arr2.push_back(value);
}
for(int xy=0; xy<n; xy++){if(arr[xy]>H){return 0;}} //ensuring that all stacks have no.of boxes less than max. height
if(arr2.size()<1 || arr2.size()>10e5 || n<1 || n>10e5 || H<1 || H>10e8){return 0;} //constraints given in the que.
int k=0; //creating a variable to keep count of how many programs we have already executed
while(k<arr2.size()){
if(arr2[k] == 1){MoveLeft();}
else if(arr2[k]==2){MoveRight(n);}
else if(arr2[k]==3){PickBox(arr, i);}
else if(arr2[k]==4){Dropbox(arr, i);}
else if(arr2[k]==0){k=arr2.size();}
k++;
}
for(int j=0; j<n; j++){std::cout<< arr[j] << " ";} //printing the arr after executing the code
return 0;
}
This is a question from a past year ZCO. And the above code is what I wrote to solve the prob.
The four functions Moveleft, MoveRight, Pickbox, Dropbox have been defined in the same file but aren't shown here because I think there's no issue with them.
When I submit the code, all test cases passed except 2. I don't know what is the problem with my code. Pls help me.
I have tried my best to make the code readable. Sorry if the code looks messy.
With the method you're trying to define an array with a user-input length is unfortunately invalid in C++.
But fortunately, there are basically two methods use to allocate arrays dynamically.
Method 1: Using Vectors
Vector is an important part of C++. It has a lot of features (e.g. its size don't need to be defined static unlike a normal array does, can redefine array size, etc.) An example's given:
#include <iostream>
#include <vector>
int main(void) {
std::vector<int> vArray; // vector<> declaration
int size = 0;
int getInput = 0;
std::cout << "Enter an array size: ";
std::cin >> size;
for (int i = 0; i < size; i++) {
std::cout << "Enter a value: ";
std::cin >> getInput;
vArray.push_back(getInput); // inserts one+ container and data in it
}
for (int i = 0; i < vArray.size(); i++) {
// retrieving contained data...
std::cout << vArray[i] << std::endl;
}
return 0;
}
Method 2: Using 'new' Keyword with Pointed Variable
The simple use of new will help you to achieve your requirement. It's less recommended since already there's concept of vectors which actually works efficiently than arrays. Let's take a look into a simple program:
#include <iostream>
int main(void) {
int *pArray;
int size;
std::cout << "Enter an array size: ";
std::cin >> size;
pArray = new int[size]; // initializing array with dynamic size
for (int i = 0; i < size; i++) {
std::cout << "Enter value: ";
std::cin >> pArray[i];
}
for (int i = 0; i < size; i++) {
std::cout << pArray[i] << std::endl;
}
delete[] pArray;
return 0;
}
Both are nice options to work with, but it's recommended by most using vector<>.
i searched a lot here, but there is no right explanation for me, for an advanced newbie in c++. I worked before with vector of structs and now I get segmentation faults...
Thats why I want to know how such objects actually works and if it is the right the way I am doing!
I have a struct like
struct numberOfSpecies {
int predator;
int prey1;
int prey2;
};
and a vector of it:
std::vector<numberOfSpecies> size;
Before I resize it and fill it with values.
size.resize(100);
what is actually this doing? Is this right for a struct?
It looks like it is initialized with zeros...
Now I am doing this like:
size[t].predator=0;
size[t].prey1=0;
size[t].prey2=0;
for(int k = 0; k < N; ++k){
size[t].predator++;
size[t].prey1++;
size[t].prey2++;
}
Is this right? Where are possible issues? How to do it better?
The easiest and 'correct' solution here is probably to just use the resize() function that belongs to the vector object with aggregate initialization (if you have access to c++11 and on), something like
size.resize(100,{0,0,0}); //aggregate initialization
for(int k = 0; k < N; ++k)
{
size[t].predator++;
size[t].prey1++;
size[t].prey2++;
}
All members of each numberOfSpecies object will be initialized to 0.
This:
size[t].predator=0;
size[t].prey1=0;
size[t].prey2=0;
will write zeros to the tth element of size - that may or may not be useful:
This:
for(int k = 0; k < N; ++k){
size[t].predator++;
size[t].prey1++;
size[t].prey2++;
}
will increment the tth element of size N times. This seems incredibly unlikely to be useful. I think what you want is:
size[0].predator=0; // Technically not needed because .resize()
size[0].prey1=0; // will have initialized it to zero anyway
size[0].prey2=0; // *BUT* explicit is always better than implicit.
// Initialize each element of size to be one greater than previous.
for(int k = 1; k < N; ++k){
size[k].predator = size[k-1].predator + 1;
size[k].prey1 = size[k-1].prey1 + 1;
size[k].prey2 = size[k-1].prey2 + 1;;
}
Use the value parameter for static parameters.
#include <vector>
struct foo{
int g;
int h;
int l;
};
int main()
{
std::vector<foo> manyFoo(10, {0});
manyFoo.resize(60, {0});
}
If you want to grow your vector as you also put arbitrary values into the struct you could ->
#include <iostream>
#include <vector>
struct foo{
foo(int aG,int aH, int aL):g(aG),h(aH),l(aL) {};
int g;
int h;
int l;
};
int main() {
std::vector<foo> lVec;
for (int i=0;i<10;i++) {
lVec.emplace_back(foo(i,i*2,i*4));
}
int lPos=0;
for (auto &rFoo: lVec) {
std::cout << "Item pos" << lPos++ << " g:" << rFoo.g << " h:" << rFoo.h << " l:" << rFoo.l << std::endl;
}
return EXIT_SUCCESS;
}
If you know the size of the vector and you want to populate it you could ->
#include <iostream>
#include <vector>
struct foo{
foo(int aG,int aH, int aL):g(aG),h(aH),l(aL) {};
int g;
int h;
int l;
};
int main() {
std::vector<foo> lVec(10,{0,0,0});
int lPos = 0;
for (auto &rFoo: lVec) {
rFoo = foo(lPos,lPos*2,lPos*4);
lPos++;
}
lPos=0;
for (auto &rFoo: lVec) {
std::cout << "Item pos" << lPos++ << " g:" << rFoo.g << " h:" << rFoo.h << " l:" << rFoo.l << std::endl;
}
return EXIT_SUCCESS;
}
You could add an default constructor to your structure. The new code will look something like this:
struct numberOfSpecies {
numberOfSpecies (): predator(0), prey1(0), prey2(0) { } // default constructor
int predator;
int prey1;
int prey2;
};
That way, your structure will be properly initialized inside your vector when resize is applied.
If i had an array of lets say 15 elements is there anyway for me to make it into a 2d array having it 5x3?
Or if i had a string with 15 letters would it be possible to make it into a 2d array having it 5x3?
This is what i have(using variables but using 5 as a and 3 as b in console)
void finishMap(string map, int a, int b)
{
string finalMap[a][b];
for(int i = 0; b>i; i++)
{
for(int x = 0; a>x; x++)
{
finalMap[a][b] += {{map[x]}, {i}};
}
}
}
Also pretty new to c++ so if you see anything i shouldn't be please tell me :3
I'm using char arrays (c strings) in my answer because I think they are useful to illustrate how arrays work - and thre really isn't a point in using std::string in your case. std::string hides a lot of the underlying nuts and bolts so I would generally recommend to play around with C strings first to understand how std::string works. Also, check out this tutorial: http://www.cplusplus.com/doc/tutorial/arrays/
A 2-dimensional array has the same memory layout as a 1-d array. In terms of memory layout, char[3][5] is the same as char[3*5] is the same as char[15]. You can use a 1-d array as a 2-d array using char[column+row*width]. The only difference if you use subscripts is that the compiler remembers how many dimensions there are and will do the whole column+row*width calculation for you.
Take this example:
char temp[5] = "abcd"; //need 5 for string termination char `\0`
for(int i = 0; i < 4; ++i) {
std::cout << temp[i];
}
std::cout << "\n\n";
for(int i = 0; i < 2; ++i) {
for(int j = 0; j < 2; ++j) {
std::cout << temp[j+2*i];
}
std::cout << std::endl;
}
Will print:
abcd
ab
cd
You can always access an array in strides. Here's a possible example using templates to restride a 1D array as a 2D array:
template <typename T, unsigned int N1, unsigned int N2>
struct strider
{
using array_type = T[N1 * N2];
array_type & data_;
Strider(array_type & data) : data_(data) {}
T & operator()(std::size_t i1, std::size_t i2)
{
return data_[i1 * N2 + i2];
}
};
template <unsigned int N1, unsigned int N2, T>
strider<T, N1, N2> stride(T (&a)[N1, N2]) { return {a}; }
Usage:
int a[15] = {};
strider<int, 3, 5> s(a);
s(1, 2) = 20;
assert(a[7] == 20);
stride<5, 3>(a)(4, 2) = 10;
assert(a[14] == 10);
I've overloaded operator() for the strided access, since unlike operator[] it can have arbirary signatures.
With some more work you could make the rank of the strided view variadic.
Okey so i used something a bit different then what i mentioned. What i did was have the user enter 3 lines of 5 length letters, which i figured out how to add into the 2d array. If your having the same issue as me, heres my code:
int main()
{
string path;
int a, b;
cin >> a >> b;
string finalMap[a][b];
for(int i = 0; b>i; i++){
cin >> path;
for(int x = 0; a>x; x++){
finalMap[x][i] = (path[x]);
}
}
for(int x = 0; b>x; x++)
{
for(int y = 0; a>y; y++)
{
cout << finalMap[y][x];
}
cout << endl;
}
return 0;
}
Thanks for trying tho, really appreciate it ^.-
You can try to use reinterpret_cast. Complete example:
#include <iostream>
using namespace std;
typedef char mtrx[5][3];
int main(){
char data[15] = "Some String";
mtrx &m = *reinterpret_cast<mtrx*>(&data);
m[1][2] = '*';
cout << data << endl;
return 0;
}
I need to compare two arrays and output another array that shows common elements.
The output I'm expecting with my code is: 0000056789.
Help will be appreciated.
#include <iostream>
using namespace std;
const int CE = 10;
const int TOP = CE-1;
int iArr1[CE]={0,1,2,3,4,5,6,7,8,9};
int iArr2[CE]={5,6,7,8,9,10,11,12,13,14};
int iArr3[CE]={0,0,0,0,0,0,0,0,0,0};
void main()
{
int i;
int j;
int iCarr3 = 0;
for(i=0; i<=TOP; i++)
{
for (j=0; j<=TOP; j++)
{
if (iArr1[i]==iArr2[j])
{
iCarr3++;
iArr3[iCarr3]=iArr2[j];
}
}
}
cout << iCarr3 << endl;
cout << iArr3;
getchar();
}
you are printing the address of your array
to print the elements of an array
for (int i = 0; i < size; i++) // keep track of the size some how
cout<<iArr3[i]<<" ";
P.S: consider sorting the arrays first, and ckecking if iArr1[i] > iArr2[j]that way you won't need to scan all the elements on eavh pass
C++ has a set_intersection algorithm in the Standard Library:
#include <iostream>
#include <algorithm>
int main()
{
const int CE = 10;
int iArr1[CE] = {0,1,2,3,4,5,6,7,8,9};
int iArr2[CE] = {5,6,7,8,9,10,11,12,13,14};
int iArr3[CE] = {0,0,0,0,0,0,0,0,0,0};
std::set_intersection(std::begin(iArr1), std::end(iArr1),
std::begin(iArr2), std::end(iArr2),
std::begin(iArr3));
std::copy(std::begin(iArr3), std::end(iArr3), std::ostream_iterator<int>(std::cout, " "));
}
Output
5 6 7 8 9 0 0 0 0 0
Note
If your arrays aren't already sorted, you could put the data into a std::set first, since std::set_intersection() requires the inputs to be sorted.
Ok I hope this is not homework. The way you have it, the output will be 5678900000. For the output to be as you want change your code to be as such:
for(i=0; i<=TOP; i++)
{
for (j=0; j<=TOP; j++)
{
if (iArr1[i]==iArr2[j])
{
iArr3[iCarr3]=iArr2[j];
}
}
iCarr3++;
}
Then for the output do this:
for(int k = 0; k <= iCarr3; k++)
std::cout << iArr3[iCarr3] << " ";
As your array are sorted, use std::set_intersection. Otherwise you just have to std::sort them before.
But never forget to use the STD library, the code is a lot more compact and readable... And most of the time less buggy and faster that what you'll come with.
http://ideone.com/c3xE3m
#include <algorithm>
#include <iostream>
#include <iterator>
const size_t CE = 10;
int iArr1[CE]={0,1,2,3,4,5,6,7,8,9};
int iArr2[CE]={5,6,7,8,9,10,11,12,13,14};
int iArr3[CE]={0,0,0,0,0,0,0,0,0,0};
int main(int argc, char const *argv[])
{
auto end_elemnt =
std::set_intersection(iArr1, iArr1 + CE,
iArr2, iArr2 + CE,
iArr3);
std::copy(iArr3, end_elemnt, std::ostream_iterator<int>(std::cout, ", "));
return 0;
}
Here is the output:
$ ./a.exe
5, 6, 7, 8, 9,
I have this array:
array[0] = 18;
array[1] = -10;
array[2] = 2;
array[3] = 4;
array[4] = 6;
array[5] = -12;
array[6] = -8;
array[7] = -6;
array[8] = 4;
array[9] = 13;
how do I sort the array in asc/desc mode in C++?
To sort an array in ascending, use:
#include <algorithm>
int main()
{
// ...
std::sort(array, array+n); // where n is the number of elements you want to sort
}
To sort it in descending, use
#include <algorithm>
#include <functional>
int main()
{
// ...
std::sort(array, array+n, std::greater<int>());
}
You can pass custom comparison functor to the std::sort function.
Well first I'm hoping your array assignment was just an error when posting but all your numbers are being assigned to the same memory location. There's nothing to sort.
After that, you can use the sort() function. The example linked shows an easy method for using it. Note that there is a third parameter that's not being used that will specify how to compare the elements. By default if you don't specify the parameter it uses 'less-than' so you get an ascending order sort. Change this to specify 'greater-than' comparator to get a descending order sort.
#include <iostream>
#include <stdlib.h>
using namespace std;
int main (int argc, char *argv[])
{
int num[10]={18,-10,2,4,6,-12,-8,-6,13,-1};
int temp;
cout << "Ascending Sort : \n\n";
for(int i=0; i<=10; i++)
{
for(int j=i+1; j<=10; j++)
{
if(num[i]>num[j])
{
temp=num[i];
num[i]=num[j];
num[j]=temp;
}
}
cout << num[i] << "\n";
}
cout << "\nDescending Sort : \n\n";
for(int i=0; i<=10; i++)
{
for(int j=i+1; j<=10; j++)
{
if(num[i]<num[j])
{
temp=num[j];
num[j]=num[i];
num[i]=temp;
}
}
cout << num[i] << "\n";
}
return 0;
}
Generally, you can just swap the two variables in
http://www.cplusplus.com/reference/algorithm/sort/
Change
bool myfunction (int i,int j) { return (i<j); }
to
bool myfunction (int i,int j) { return (j<i); }
you can rename it to something else so that you have two comparison functions to use when the result needs to be ascending or descending.
If the function body has complicated expressions and involves i and j multiple times, then it is easier to swap the i and j in the parameter list instead of every i and j in the body:
bool myfunction (int j,int i) { return (i<j); }
The same goes for
http://www.cplusplus.com/reference/clibrary/cstdlib/qsort/