Replace element in array by average - c++

I have a question about the exercise from my course:
Write a program that takes array of real numbers as parameter and replaces each element that is smaller than average of the first and last element, by this average. This is my code:
#include <iostream>
#include <string>
using namespace std;
void replaverage(int arr[], int n)
{
for (int i; i < 6; i++) {
cout << "Enter the numbers" << endl;
cin >> arr[i];
}
int f = arr[0];
int l = arr[n - 1];
double av = f + l / 2;
for (int i; i < n; i++) {
if (arr[i] < av) {
arr[i] = av;
}
}
}
int main()
{
int n;
int arr[n];
replaverage(arr, n);
cout << arr << " " << endl;
return 0;
}
Code is working, however as an output, it is giving some kind of address "0x7fff2306a5c0". I'm beginner so I apologize, maybe my error is stupid but I don't know how to fix it. Thanks for helping!

#include <iostream>
#include <string>
using namespace std;
void replaverage(int arr[], int n)
{
for (int i = 0; i < n; i++) {
cout << "Enter the number: ";
cin >> arr[i];
cout << endl;
}
int f = arr[0];
int l = arr[n - 1];
double av = (f + l) / 2;
for (int i = 0; i < n; i++) {
if (arr[i] < av) {
arr[i] = av;
}
}
}
int main()
{
int n = 6; // Making 6 since you had it hardcoded
int arr[n];
replaverage(arr, n);
for (int i = 0; i < n; i++) {
cout << arr[i] << endl;
}
return 0;
}
First problem: Initialize your loop counters to 0;
Second problem: Initialize n in main being passed as parameter to
something
Third problem: Your average calculation is incorrect. It should be (f+l) / 2. Otherwise it will be doing l/2 + f, which is incorrect.
Fourth problem: You need to loop over your array to see all the
elements

Related

swap alternate in an array

You have been given an array/list(ARR) of size N. You need to swap every pair of alternate elements in the array/list.
You don't need to print or return anything, just change in the input array itself.
#include <iostream>;
using namespace std;
void printArr(int arr[], int n)
{
for (int i = 0; i < n; i++)
cout << arr[i]<<i;
}
void UpdateArr(int arr[], int n)
{
int i = 0, j = n - 1;
while (i < j) {
int temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
i += 2;
j -= 2;
}
cout<<' printArr(arr[], n)';
}
int main()
{
int t;
cin>> t;
int n;
cin>> n;
int input[100];
for(int i=0; i<n; i++) {
cin >>input[i];
}
int arr[100] ;
n = sizeof(arr) / sizeof(arr[0]);
UpdateArr(arr, n);
return 0;
}
I'm not sure what are you exactly expecting the output to be (pls edit it and show the expected output) but I think this is what you need to do
#include <iostream>
#include <iomanip>
using namespace std;
void UpdateArray(int Arr[], size_t n) {
for (size_t i = 0; i < n / 2; i++) {
int Holder = Arr[i];
Arr[i] = Arr[~i + n];
Arr[~i + n] = Holder; } }
int main() {
int Arr[7] = { 1,2,3,4,5,6,7 };
UpdateArray(Arr, 7);
for (int i = 0; i < 7; i++) {
std::cout << Arr[i] << "\n"; }
return 0; }
size_t is like an int but it can't go into negative, but it can take bigger positive numbers, you can replace it with int, it shouldn't make a difference.
so we loop through half the array, replacing first items with last, the [~i + n] flips the value to the other side, so like index 4 in a array size of 20 will become 15

A number K and an Array of size N is given, check whether we can get the sum of any two elements of array equal to K

I tried to solve the problem but my code still contains some bugs. Why isn't it running?
Here is the link of the question website: https://www.hackerearth.com/practice/data-structures/hash-tables/basics-of-hash-tables/practice-problems/algorithm/pair-sums/?
#include <iostream>
#include <bits/stdc++.h>
using namespace std;
const int n = 1e7 + 10;
int hsh[n];
int main()
{
int n, k;
cin >> n >> k;
int A[n];
for (int i = 0; i < n; i++)
{
cin >> A[i];
}
for (int i = 0; i < n; i++)
{
hsh[A[i]] = k - A[i];
}
int t = 0;
for (int i = 0; i < n; i++)
{
if (hsh[A[i]] == k - hsh[hsh[A[i]]])
{
cout << "YES";
t = 1;
break;
}
}
if (t == 0)
{
cout << "NO";
}
return 0;
}
The problem is that while hsh[A[i]] is always valid, hsh[hsh[A[i]] is not.
Consider the following input:
1 1
10000
This does the following:
A[0] = 10000;
...
hsh[10000] = 1 - 10000; // = -99999
...
if (hsh[10000] == 1 - hsh[-99999]) {...}
So your code is reading out of bounds of the array hsh[]. Make sure you check first if hsh[A[i]] >= 0.
Note that your code is more complicated than necessary; you can do a single loop over the input to check if there is a matching pair:
#include <iostream>
static constexpr int max_k = 2e6;
static bool seen[max_k + 1];
int main()
{
int n, k;
std::cin >> n >> k;
for (int i = 0; i < n; ++i)
{
int A;
std::cin >> A;
if (A <= k && seen[k - A]) {
std::cout << "YES\n";
return 0;
}
seen[A] = true;
}
std::cout << "NO\n";
}

I am unable to get my code to get the stride of 7 to work properly C++

The question I am trying to solve is the following:
Write a function that traverses (and prints) the element of an array with stride =7. To do this the update part in the loop will be i= (i+7) % n, where n is the array size.
Would this function visit all elements of the array? Try different array sizes to check when it is impossible to traverse all elements.
The code that I wrote below doesn't print the correct values in the arry even if the value of i is correct.
Can anyone help, I would really appreciate it.
#include <fstream>
#include <stdlib.h>
using namespace std;
int* CreateArray(int n);
void StrideArray(int arr[], int n);
int main()
{
int* arr = new int[3];
arr = CreateArray(3);
cout << "The Elements In The Array Are: " << endl;
for (int i = 0; i < 3; i++)
{
cout << arr[i] << " ";
}
cout << endl;
StrideArray(arr, 3);
cout << "The Elements In The Array Stride 7 Are: " << endl;
for (int i = 0; i < 3; i++)
{
cout << arr[i] << " ";
}
delete[] arr;
return 0;
}
int* CreateArray(int n)
{
int* arr = new int[n];
for (int i = 0; i < n; i++)
{
arr[i] = (rand() % 100);
}
return arr;
}
void StrideArray(int arr[], int n)
{
int i = 0;
for (int j = 0; j < n; j++)
{
i = (i + 7) % n;
arr[j] = arr[i];
}
}
The problem is in StrideArray you read back the modified values of arr.
void StrideArray(int arr[], int n)
{
int i = 0;
int puffer=new int[n];
for (int j = 0; j < n; j++)
{
i = (i + 7) % n;
puffer[j] = arr[i];
}
for (int j = 0; j < n; j++){
puffer[j] = arr[j];
}
debete[] puffer;
}
Is a good way to write the function.
Also it visits all element only if n isn't dividable by 7. So if n is not 7,14,21,...
Also to use cout you have to #include <iostream>
Your StrideArray function needs fixing; you are iterating over j but using i to index, which remains constant; and you are reassigning value at one index to another where as you are supposed to print it:
void StrideArray(int arr[], int n)
{
int i = 0;
for (int j = 0; j < n; j=j+7)
{
cout << arr[j] << endl;
}
}
I modified the rest of your code for demo:
#include <iostream>
#include <stdlib.h>
using namespace std;
int* CreateArray(int n);
void StrideArray(int arr[], int n);
int main()
{
int* arr = new int[3];
arr = CreateArray(21);
cout << "The Elements In The Array Are: " << endl;
for (int i = 0; i < 21; i++)
{
cout << arr[i] << " ";
}
cout << endl;
StrideArray(arr, 21);
delete[] arr;
return 0;
}
int* CreateArray(int n)
{
int* arr = new int[n];
for (int i = 0; i < n; i++)
{
arr[i] = (rand() % 100);
}
return arr;
}

What's wrong with factorial function code in this Pascal triangle?

can anyone explain why first fact() function code doesn't give me correct output but second one does?
what's wrong with the commented factorial function code???
#include <iostream>
using namespace std;
// int fact(int n){
// for (int i = n-1; i > 0; i--){
// n = n * i;
// }
// return n;
// }
int fact(int n){
int temp=1;
for (int i = 2; i <=n; i++){
temp= temp * i;
}
return temp;
}
int nCr(int n, int r){
int temp=(fact(n) / (fact(n - r) * fact(r)));
return temp;
}
int main(){
int n;
cout << "enter no: ";
cin >> n;
for (int i = 0; i < n;i++){
for (int k = 1; k < (n - i);k++)
cout << " ";
for (int j = 0; j <= i; j++)
{
cout << nCr(i, j) << " ";
}
cout << endl;
}
return 0;
}
The second fact function correctly returns 1 when n = 0, but the first one wrongly returns 0 when n = 0.
Adding check for this case will make the first function work well.
int fact(int n){
if (n == 0) return 1; // check for n = 0 case
for (int i = n-1; i > 0; i--){
n = n * i;
}
return n;
}

How to implement insertion sort algorithm in C++ with arrays and pointers?

I am trying to learn C++, arrays and pointers. I decided to implement the insertion sort algorithm. So, here is my code and my wrong output. What should I do to correct it? Can you please tell me what is my mistake and what should I avoid if it is a common error?
My code:
// InsertionSort.cpp
#include "stdafx.h"
#include <iostream>
int DeclareAnInteger();
int* DeclareAndShowTheArray(int n);
int* InsertionSort(int *A, int n);
int main()
{
int n = DeclareAnInteger();
int *A;
A = DeclareAndShowTheArray(n);
int *B;
B = InsertionSort(A, n);
system("PAUSE");
return 0;
}
int DeclareAnInteger()
{
int n;
std::cout << "Please enter a positive integer n: ";
std::cin >> n;
return n;
}
int* DeclareAndShowTheArray(int n)
{
int *A;
A = (int *)alloca(sizeof(int) * n);
for (int i = 0; i < n; i++)
{
std::cout << "Please enter the value of A[" << i + 1 << "]: ";
std::cin >> A[i];
}
std::cout << "The unsorted array is: ";
for (int i = 0; i < n; i++)
{
std::cout << A[i];
std::cout << "\t";
}
std::cout << "\n";
return A;
}
int* InsertionSort(int *A, int n)
{
int k;
//int *A = new int[n];
for (k = 1; k < n; k++)
{
int key = A[k];
int m = k - 1;
while (m >= 0 & A[m] > key)
{
A[m + 1] = A[m];
m = m - 1;
}
A[m + 1] = key;
}
std::cout << "The sorted array is: ";
for (int i = 0; i < n; i++)
{
std::cout << A[i];
std::cout << "\t";
}
std::cout << "\n" << std::endl;
return A;
}
My output:
This here is a big problem:
A = (int *)alloca(sizeof(int) * n);
The alloca function allocates on the stack, and it will be lost when the function returns which gives you a stray pointer and undefined behavior when you dereference this pointer.
If you're programming C++ then use new, if you program C then use malloc.