Return reference [closed] - c++

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My expected output of the following code is "1 -1 3 4 5 6".
(arr[1]=2 should change to arr[1]=-1). When I run this code,
nothing changes, and I can't understand why.
What would be the difference if parameter "seek" will be received by "find" function by value and not by reference?
When I declare that "seek" is a value, the program not running (0xC0000005)... but why does this happen?
#include <iostream>
int& find (int arr[], int size, int& seek)
{
for (int i; i<size; i++) {
if (arr[i]==seek) return arr[i];
}
return seek;
}
void print (int arr[], int size)
{
for (int i=0; i<size; i++) {
std::cout << arr[i] << " ";
}
std::cout << std::endl;
}
int main ()
{
int arr[]={1,2,3,4,5,6};
int size = sizeof arr / sizeof *arr;
int seek=2;
find (arr, size, seek) = -1;
print(arr, size);
return 0;
}

for (int i; i<size; i++) {
You need to initialise i here
for (int i = 0; i<size; i++) {
As for the second part - see #Some programmer dude's comment

Related

sum of array elements using recursion [closed]

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#include<iostream>
using namespace std;
int getSum(int *arr, int size) {
if(size == 0) {
return 0;
}
if(size == 1 )
{
return arr[0];
}
int remainingPart = getSum(arr+1, size-1);
int sum = arr[0] + remainingPart;
return sum;
}
int main() {
int arr[100], n;
cin >> n;
for(int i = 0; i < n; i++){
cin >> arr[n];
}
int sum = getSum(arr, n);
cout << "Sum is " << sum << endl;
return 0;
}
OUTPUT
3
1
2
3
Sum is -1827678256
When i run the code with custom input it gives the correct output. But when i input data from the user it gives an incorrect answer. Why so?
cin >> arr[n];
should be
cin >> arr[i];

my program wont work properly and my function keeps throwing segmentation fault [closed]

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Closed 3 years ago.
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so I have this code that with a function is supposed to take all the numbers in a 2D array and print them to the second power but my code keeps throwing segmentation fault and i don't know why
#include <bits/stdc++.h>
using namespace std;
void er(int arr[][100000000], int, int);
int main()
{
int n, m;
cin >> n >> m;
int arr[n][100000000];
er(arr, n, m);
return 0;
}
void er(int arr[][100000000], int n, int m)
{
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cin >> arr[i][j];
arr[i][j] *= arr[i][j];
}
}
for (int i = 0; i < n; i++) {
for (int j = 0; j < m; j++) {
cout << arr[i][j];
}
}
}
Using
int arr[n][100000000];
is problematic on two accounts.
VLAs are not standard C++. It is supported by some compilers as an extension.
The size 100000000 is too large for a variable on the stack. Changing that to 100 and making sure that m is less than or equal to 100 will most likely work as long as your compiler supports VLAs.
A better alternative would be to use std::vector.
int n, m;
cin >> n >> m;
std::vector<std::vector<int>> arr(n, std::vector<int>(m));
Of course, that will require you to change the function er accordingly.
In addition, please don't use
#include <bits/stdc++.h>
See Why should I not #include <bits/stdc++.h>? for further details.

Code is printing only one multiple instead of 3 [closed]

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I was writing a code which displayed first three multiples of an integer using functions. But here when I run this it shows only the first multiple.
#include <iostream>
#include <vector>
// Defined first_three_multiples() here:
std::vector <int> first_three_multiples(int num) {
std::vector <int> output;
for (int i=1; i<4; i++) {
output.push_back(num*i);
return output;
}
}
int main() {
for (int element : first_three_multiples(8)) {
std::cout << element << "\n";
}
}
Expected Output: 8 16 24
Actual Output: 8
You have put the return statement inside the for loop. It is advised to follow proper code indentations in order to avoid these kind of errors from happening again.
#include <iostream>
#include <vector>
std::vector<int> first_three_multiples(int num)
{
std::vector<int> output;
for (int i = 1; i < 4; i++) {
output.push_back(num * i);
# you put a return statement here, which returns only 8
}
return output; # this would return all three values
}
int main()
{
for (int element : first_three_multiples(8)) {
std::cout << element << "\n";
}
}
Simple error
for (int i=1; i<4; i++) {
output.push_back(num*i);
return output;
}
should be
for (int i=1; i<4; i++) {
output.push_back(num*i);
}
return output;
It pays to get your indentation right as it makes errors like this much easier to spot (and avoid in the first place).

Problem with calculating Primes within a given Range in C++ [closed]

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Closed 3 years ago.
Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question.
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Im trying to create a program that does various math operations, and i wanted to start with calculating prime numbers within a given range. However, when i try to execute the code, it just returns exit status -1. What is wrong with the program and how do i fix it?
#include <iostream>
#include <vector>
using namespace std;
void getPrimes(int min, int max) {
int range = max - min;
std::vector< int > possible_values;
for (int q = 0; q < range; q++) {
possible_values.push_back(min + q);
}
for (int i = 0; i < range; i++) {
int num_of_factors = 0;
int num = possible_values.at(i);
for (int c = 0; c < num; c++) {
if (num % c == 0) {
num_of_factors++;
}
}
if (num_of_factors == 0) {
std::cout << num << endl;
}
}
}
int main() {
int min, max;
std::cout << "min: ";
std::cin >> min;
std::cout << "max: ";
std::cin >> max;
getPrimes(min, max);
}
this loop should start from 2 because :
c%0 is undefined behavior
every number %1 is 0 so you can see why num_of_factors is never 0
for (int c = 2; c < num; c++) {
if (num % c == 0) {
num_of_factors++;
}
}

issue with std vector in c++ [closed]

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Closed 7 years ago.
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I have an issue with my code, I can fill the table but when I display it, it display 0 for me, here is my code
#include<iostream>
#include<vector>
using namespace std;
int n;
void lire_tab(vector<int> A);
void tri_tab(vector<int> A);
void aff_tab(vector<int> A);
int main()
{
cout<<"donnez la taille du tableau: ";
cin>>n;
vector<int> A(n);
lire_tab(A);
aff_tab (A);
tri_tab (A);
aff_tab (A);
return 0;
}
void lire_tab(vector<int> A)
{
for(int i=0;i<n;i++)
{
cout<<"A["<<i<<"]= ";
cin>>A[i];
}
cout<<"________________________"<<endl;
}
void tri_tab(vector<int> A)
{
int temp;
temp=0;
for(int i=0; i<n; i++)
{
for(int j=0; j<n; j++){
if(A[i]<A[j])
{
temp = A[i];
A[i] = A[j];
A[j] = temp;
}
}
}
}
Can you help me please, I'm really lost in this, I don't really figure out why it print 0
Your functions are using passing by value, therefore, a copy is seen within the function.
Please read about passing by reference
void lire_tab(vector<int>& A);
Instead of accepting the vector by value
void lire_tab(vector<int> A)
You want to accept the vector by reference
void lire_tab(vector<int>& A)
Otherwise you are only modifying a function-local copy of your vector, not the original vector that was passed in.