I am new to c++ language. I am trying to solve a problem using function. I have to print the pentagon numbers untill the integer input, but when function returns the values, it only prints one value. I would love some help with it.
#include<iostream>
using namespace std;
int pent(int num){
int p;
for(int i=1;i<=num;i++){
p=(i*(3*i-1)/2);
}
return p;
}
int main(){
int num;
cin>>num;
int sender=pent(num);
cout<<sender<<endl;
return 0;
}
Your function returns int, that is a single integer. To return more, you can use std::vector. As you probably are not familiar with it, I will give you some pointers...
The most simple constructor creates a vector with no entries:
std::vector<int> x;
You can reserve space for elements via reserve:
x.reserve(num);
The vector still has no elements, but it already allocated enough space to hold num elements. This is important, because when we will add elements the vector will grow and that potentially requires to copy all elements to a different place in memory. We can avoid such frequent reallocations by reserving enough space upfront.
To add elements to the vector you can use push_back:
x.push_back(42);
Eventually to print all elements of the vector we can use a range-based for loop:
for (auto element : x) std::cout << element << " ";
So you can rewrite your code like this:
#include <iostream>
#include <vector>
std::vector<int> pent(int num){
std::vector<int> result;
result.reserve(num);
for(int i=1;i<=num;i++){
result.push_back(i*(3*i-1)/2);
}
return result;
}
int main(){
int num;
std::cin >> num;
auto sender = pent(num);
for (auto number : sender) std::cout << number << " ";
}
In your program, from your pent() function you are only returning last calculated value. In you ever time, you are overwriting you variable p.
So there is a way which #asmmo is suggesting, to print in pent() function.
Or you can pass a vector to your pent() function and store values in that and print it in main function.
For your ref:
void pent(int num, vector<int> &arr) {
int p;
for (int i = 1; i <= num; i++) {
arr[i-1] = (i*(3 * i - 1) / 2);
}
}
int main() {
int num;
cin >> num;
vector<int> arr(num);
pent(num, arr);
for (int i = 0; i < num; i++) {
cout << arr[i] << endl;
}
return 0;
}
Related
I was trying to store numbers in an array. The first half of the array are numbers that are ascending 1,2,3,4,5 etc and the second half of the array are random numbers. When i run the program it produces the output I wanted but gives me the error please help
#include <iostream>
#include <cstdlib>
using namespace std;
class sorting {
private:
int size, elements;
int arr[NULL];
public:
void sort(){
cout << "Enter number of desired elements" << ">"; cin >> elements;
arr[elements];
half();
}
void half() {
for (int i = 0; i < elements/2; i++) {
arr[i] = i + 1;
}
for (int i = elements / 2; i < elements; i++) {
arr[i] = rand();
}
cout << "This is the elements of the array";
for (int i = 0; i < elements; i++) {
cout << arr[i] << " ";
}
}
};
int main()
{
sorting sortObject;
sortObject.sort();
return 0;
}
As i could see you want the array size to change during run time depending on the input, we need to dynamically allocate a array.so take a integer pointer as a field instead of static array.
then inside the sort function after reading the input, dynamically allocate the memory to pointer.(actually its better if we do it in a constructor).
int *arr;
arr=(int *)malloc(elements*sizeof(int));
Program in C++ that takes 3 numbers and send them to a function and then calculate the average function of these 3 numbers.
I know how to do that without using a function ,for example for any n numbers I have the following program:
#include<stdio.h>
int main()
{
int n, i;
float sum = 0, x;
printf("Enter number of elements: ");
scanf("%d", &n);
printf("\n\n\nEnter %d elements\n\n", n);
for(i = 0; i < n; i++)
{
scanf("%f", &x);
sum += x;
}
printf("\n\n\nAverage of the entered numbers is = %f", (sum/n));
return 0;
}
Or this one which do that using arrays:
#include <iostream>
using namespace std;
int main()
{
int n, i;
float num[100], sum=0.0, average;
cout << "Enter the numbers of data: ";
cin >> n;
while (n > 100 || n <= 0)
{
cout << "Error! number should in range of (1 to 100)." << endl;
cout << "Enter the number again: ";
cin >> n;
}
for(i = 0; i < n; ++i)
{
cout << i + 1 << ". Enter number: ";
cin >> num[i];
sum += num[i];
}
average = sum / n;
cout << "Average = " << average;
return 0;
}
But is it possible to use functions?if yes then how? thank you so much for helping.
As an alternative to using fundamental types to store your values C++ provides std::vector to handle numeric storage (with automatic memory management) instead of plain old arrays, and it provides many tools, like std::accumulate. Using what C++ provides can substantially reduce your function to:
double avg (std::vector<int>& i)
{
/* return sum of elements divided by the number of elements */
return std::accumulate (i.begin(), i.end(), 0) / static_cast<double>(i.size());
}
In fact a complete example can require only a dozen or so additional lines, e.g.
#include <iostream>
#include <vector>
#include <numeric>
double avg (std::vector<int>& i)
{
/* return sum of elements divided by the number of elements */
return std::accumulate (i.begin(), i.end(), 0) / static_cast<double>(i.size());
}
int main (void) {
int n; /* temporary integer */
std::vector<int> v {}; /* vector of int */
while (std::cin >> n) /* while good integer read */
v.push_back(n); /* add to vector */
std::cout << "\naverage: " << avg(v) << '\n'; /* output result */
}
Above, input is taken from stdin and it will handle as many integers as you would like to enter (or redirect from a file as input). The std::accumulate simply sums the stored integers in the vector and then to complete the average, you simply divide by the number of elements (with a cast to double to prevent integer-division).
Example Use/Output
$ ./bin/accumulate_vect
10
20
34
done
average: 21.3333
(note: you can enter any non-integer (or manual EOF) to end input of values, "done" was simply used above, but it could just as well be 'q' or "gorilla" -- any non-integer)
It is good to work both with plain-old array (because there is a lot of legacy code out there that uses them), but equally good to know that new code written can take advantage of the nice containers and numeric routines C++ now provides (and has for a decade or so).
So, I created two options for you, one use vector and that's really comfortable because you can find out the size with a function-member and the other with array
#include <iostream>
#include <vector>
float average(std::vector<int> vec)
{
float sum = 0;
for (int i = 0; i < vec.size(); ++i)
{
sum += vec[i];
}
sum /= vec.size();
return sum;
}
float average(int arr[],const int n)
{
float sum = 0;
for (int i = 0; i < n; ++i)
{
sum += arr[i];
}
sum /= n;
return sum;
}
int main() {
std::vector<int> vec = { 1,2,3,4,5,6,99};
int arr[7] = { 1,2,3,4,5,6,99 };
std::cout << average(vec) << " " << average(arr, 7);
}
This is an example meant to give you an idea about what needs to be done. You can do this the following way:
// we pass an array "a" that has N elements
double average(int a[], const int N)
{
int sum = 0;
// we go through each element and we sum them up
for(int i = 0; i < N; ++i)
{
sum+=a[i];
}
// we divide the sum by the number of elements
// but we first have to multiply the number of elements by 1.0
// in order to prevent integer division from happening
return sum/(N*1.0);
}
int main()
{
const int N = 3;
int a[N];
cin >> a[0] >> a[1] >> a[2];
cout << average(a, N) << endl;
return 0;
}
how to do that without using a function
Quite simple. Just put your code in a function, let's call it calculateAverage and return the average value from it. What should this function take as input?
The list of numbers (array of numbers)
Total numbers (n)
So let's first get the input from the user and put it into the array, you have already done it:
for(int i = 0; i < n; ++i)
{
cout << i + 1 << ". Enter number: ";
cin >> num[i];
}
Now, lets make a small function i.e., calculateAverage():
int calculateAverage(int numbers[], int total)
{
int sum = 0; // always initialize your variables
for(int i = 0; i < total; ++i)
{
sum += numbers[i];
}
const int average = sum / total; // it is constant and should never change
// so we qualify it as 'const'
//return this value
return average
}
There are a few important points to note here.
When you pass an array into a function, you will loose size information i.e, how many elements it contains or it can contain. This is because it decays into a pointer. So how do we fix this? There are a couple of ways,
pass the size information in the function, like we passed total
Use an std::vector (when you don't know how many elements the user will enter). std::vector is a dynamic array, it will grow as required. If you know the number of elements beforehand, you can use std::array
A few problems with your code:
using namespace std;
Don't do this. Instead if you want something out of std, for e.g., cout you can do:
using std::cout
using std::cin
...
or you can just write std::cout everytime.
int n, i;
float num[100], sum=0.0, average;
Always initialize your variables before you use them. If you don't know the value they should be initialized to, just default initialize using {};
int n{}, i{};
float num[100]{}, sum=0.0, average{};
It is not mandatory, but good practice to declare variables on separate lines. This makes your code more readable.
I need help with this code.
What I want is to make a parametric constructor and initialise/set the value of array in it.
Question: Make a class with arrays of integers and initialise it in a constructor. Then find the smallest and largest numbers using functions.
But I am stuck at how to initialise the array in the constructor.
I want to take data input in both ways
(1) By user, using cin
(2) By giving my own values
class Numbers
{
int Arr[3];
public:
Numbers() //default constructor
{
for (int i=0 ; i<=2 ; i++)
{
Arr[i]=0;
}
}
Numbers(int arr[]) //parameteric constructor
{
for (int i=0;i<=2;i++)
{
Arr[i]=arr[i];
}
}
};
int main()
{
int aro[3] = {0,10,5};
Numbers obj (aro);
return ;
}
The solution is pretty simple. I've made a new program from start again (for sake of understanding). According to your requirement, you wants to get input of array elements from the user dynamically and assign them to a constructor and use a method to print the highest value.
Consider the following code:
#include <iostream>
using namespace std;
const int N = 100;
class Numbers
{
int largest = 0;
public:
Numbers(int, int[]);
void showHighest(void)
{
cout << largest << endl;
}
};
Numbers::Numbers(int size, int arr[])
{
for (int i = 0; i < size; i++)
{
if (arr[i] > largest)
{
largest = arr[i];
}
}
}
int main(void)
{
int arrays[N], total;
cout << "How many elements? (starts from zero) ";
cin >> total;
for (int i = 0; i < total; i++)
{
cout << "Element " << i << ": ";
cin >> arrays[i];
}
Numbers n(total, arrays);
n.showHighest();
return 0;
}
Output
How many elements? (starts from zero) 3
Element 0: 12
Element 1: 16
Element 2: 11
16
Note: I've initialized a constant number of maximum elements, you can modify it. No vectors, etc. required to achieve so. You can either use your own values by removing the total and its followed statements and use only int arrays[<num>] = {...} instead. You're done!
Enjoy coding!
I suggest to use std::vector<int> or std::array<int>.
If you want initialize with custom values you can do std::vector<int> m_vec {0, 1, 2};
Thank you so much for your help. I was basically confused about how to use arrays in a constructor and use setters/getters for arrays in a class. But you all helped a lot. Thanks again.
Numbers(int arr[])
{
for (int i=0;i<=9;i++)
{
Arr[i]=arr[i];
}
Largest=Arr[0];
Smallest=Arr[0];
}
void Largest_Number()
{
header_top("Largest Number");
Largest=Arr[0]; //Using this so we make largest value as index zero
for (int i=0 ; i<=9 ; i++)
{
if(Arr[i]>Largest)
{
setLargest( Arr[i] );
}
}
cout<<"Largest Number: "<<getLargest()<<endl;
}
I have to find the minimum and maximum value of elements in a array using divide and conquer. I have written a code but it is not working for more then 6 elements in array. I don't know whats the problem
#include<iostream>
using namespace std;
int minimum=999,maximum,mi,ma;
void result(int mi,int ma)
{
if(maximum<ma)
{
maximum=ma;
}
if(minimum>mi)
{
minimum=mi;
}
}
void maxmin(int arr[],int i,int j)
{
cout<<" i ="<<i<<" j= "<<j<<endl;
if(i==j)
{
mi=ma=arr[i];
result(mi,ma);
}
else if(i==j-1)
{
if(arr[i]>arr[j])
{
ma=arr[i];
mi=arr[j];
}
else
{
mi=arr[i];
ma=arr[j];
}
result(mi,ma);
}
else
{
int mid=i+j/2;
maxmin(arr,i,mid);
maxmin(arr,mid+1,j);
}
}
int main()
{
int arr[10],n;
cin>>n;
for(int i=0;i<n;i++)
{
cin>>arr[i];
}
maxmin(arr,0,n-1);
cout<<" max "<<maximum<<" min "<<minimum<<endl;
return 0;
}
Your code has a few mistakes
Your code reads n from the user input, but you provided only 10 sized array, and user can try to input 10+ numbers, so we will have an undefined behavior in that case.
You write it very bad and unreadable. If you want somebody else to read your code, check in the your favourite book or in the internet information about how to write beautiful and readable code.
You implemented that algorithm yourself. It is a bad habit, use the standard library algorithms and you will not encounter such mistake.
.
#include <iostream> // std::cin, std::cout
#include <cstddef> // std::size_t
#include <algorithm> // std::min_element, std::max_element
int main ()
{
std::size_t array_size;
std::cin >> array_size;
int *some_array = new int[array_size]; // Allocate memory dynamically
for(std::size_t i = 0; i < array_size; ++i)
{
std::cin >> some_array[i];
}
/* Standard library operate on iterators, they are special classes
* that have interface that is similar in many cases to pointers (so we can use pointers as iterators).
* std::min/max_element needs one iterator for the sequence beginning
* and one iterator after the end. It returns iterator to a found element.
*/
int min = *std::min_element(some_array, some_array + array_size);
int max = *std::max_element(some_array, some_array + array_size);
delete[] some_array;
std::cout << "Min = " << min << std::endl << "Max = " << max;
std::cout << std::endl;
}
Code isn't well written and first dry run your code, you will find the problem easily.
Change
else
{
int mid=i+j/2;
maxmin(arr,i,mid);
maxmin(arr,mid+1,j);
}
To
else
{
int mid=(i+j)/2; /*** Adding brackets ***/
maxmin(arr,i,mid);
maxmin(arr,mid+1,j);
}
And check the logic for calling the result function (because according to your logic the two subsets are individually calculating MIN and MAX in itself not in whole array)
#include <iostream>
using namespace std;
int main(){
int findMax(int *);
const int MAX = 100;
int values[MAX];
char ivals[256];
// Get the space-separated values from user input.
cin.getline(ivals, 256, '0');
char *helper;
// Clean input array and transfer it to values.
for(int i = 0; i < (MAX) && ivals[i] != 0; i++){
helper = ivals[i * 2];
values[i] = atoi(helper);
}
int mval = findMax(values);
cout << values << endl << mval;
return 0;
}
//Function to find the maximum value in the array
int findMax(int arr[]){
int localmax = 0;
for(int i = 0; i < (sizeof(arr)/sizeof(int)); i++){
if(arr[i] > localmax){
localmax = arr[i];
}
}
return localmax;
}
The purpose of this program is for the user to input a space-separated series of values ended by a 0. That array is then to be analyzed to find the max. I figured out how to convert what is originally a char[] into an int[] so that I can use the findMax() function on it without error but the sorting loop seems to have a problem of its own and when "cout << values << endl << mval;" is called, it returns only a memory address instead of what should be a non-spaced sequence of ints. Can anybody explain what I am doing wrong? It seems that I may have made some mistake using the pointers but I cannot figure out what.
Printing values won't print the contents of the array as you expect, it will print the memory location of the first element of the array.
Try something like this instead:
#include <iterator>
#include <algorithm>
// ...
copy(&values[0], &values[MAX], ostream_iterator(cout, " "));
Sorry I can't post actual working code, but your original post is a mess with many syntax and syntactic errors.
EDIT: In the interest of being more complete and more approachable & understandable to beginners, I've written a small program that illustrates 4 ways to accomplish this.
Method 1 uses copy with an ostream_iterator as I've done above.
Method 2 below is probably the most basic & easiest to understand.
Method 3 is a C++0x method. I know the question is tagged C++, but I thought it might be educational to add this.
Method 4 is a C++ approach using a vector and for_each. I've implemented a functor that does the dumping.
Share & Enjoy
#include <iostream>
#include <iterator>
#include <algorithm>
#include <functional>
#include <vector>
using namespace std;
struct dump_val : public unary_function<int,void>
{
void operator()(int val)
{
cout << val << " ";
}
};
int main(){
int vals[5] = {1,2,3,4,5};
// version 1, using std::copy and ostream_iterator
copy(&vals[0], &vals[5], ostream_iterator<int>(cout, " "));
cout << endl;
// version 2, using a simple hand-written loop
for( size_t i = 0; i < 5; ++i )
cout << vals[i] << " ";
cout << endl;
// version 3, using C++0x lambdas
for_each(&vals[0], &vals[5], [](int val)
{
cout << val << " ";
}
);
cout << endl;
// version 4, with elements in a vector and calling a functor from for_each
vector<int> vals_vec;
vals_vec.push_back(1);
vals_vec.push_back(2);
vals_vec.push_back(3);
vals_vec.push_back(4);
vals_vec.push_back(5);
for_each( vals_vec.begin(), vals_vec.end(), dump_val() );
cout << endl;
}
When you pass around an array of X it's really a pointer to an array of X that you're passing around. So when you pass values to cout it only has the pointer to print out.
You really should look into using some of the standard algorithms to make your life simpler.
For example to print all the elements in an array you can just write
std::copy(values, values+MAX, std::ostream_iterator<int>(std::cout, "\n"));
To find the max element you could just write
int mval = *std::max_element(values, values+MAX);
So your code becomes
#include <iostream>
using namespace std;
int main(){
const int MAX = 100;
int values[MAX];
char ivals[256];
// Get the space-separated values from user input.
cin.getline(ivals, 256, '0');
char *helper;
// Clean input array and transfer it to values.
for(int i = 0; i < (MAX) && ivals[i] != 0; i++){
helper = ivals[i * 2];
values[i] = atoi(helper);
}
copy(values, values+MAX, ostream_iterator<int>(cout, "\n"));
cout << *std::max_element(values, values+MAX);
return 0;
}
Doing this removes the need for your findMax method altogether.
I'd also re-write your code so that you use a vector instead of an array. This makes your code even shorter. And you can use stringstream to convert strings to numbers.
Something like this should work and is a lot less code than the original.
int main(){
vector<int> values;
char ivals[256];
// Get the space-separated values from user input.
cin.getline(ivals, 256, '0');
int temp = 0;
stringstream ss(ivals);
//read the next int out of the stream and put it in temp
while(ss >> temp) {
//add temp to the vector of ints
values.push_back(temp);
}
copy(values.begin(), values.end(), ostream_iterator<int>(cout, "\n"));
cout << *std::max_element(values.begin(), values.end());
return 0;
}
Array of int is promoted to a pointer to int when passed to a function. There is no operator << taking ordinary array. If you want to use operator << this way, you need to use std::vector instead.
Note: it is possible technically to distinguish array when passed to a function using template, but this is not implemented for standard operator <<.
for(int i = 0; i < (sizeof(arr)/sizeof(int)); i++){
sizeof(arr) here is the size of the pointer to the array. C++ will not pass the actual array, that would be grossly inefficient. You'd typically only get one pass through the loop. Declare your function like this:
int findMax(int* arr, size_t elements) {
//...
}
But, really, use a vector.
Oh, hang on, the question. Loop through the array and print each individual element.