Given an array of integers, find the sum of its elements. where is the error?

Question

For some reason I am not getting the desired answer and I can't fathom where the error is.

For example, given the array ar = [1,2,3], 1+2+3 = 6, so return 6, but I am getting 650462183 instead.

#include <iostream>
#include <algorithm>
#include <vector>
#include <ctime>
#include <cstdlib>
#include <cctype>
 
using namespace std;
 
int main ()
{
 int i;
 
 cout << "enter the value of i" << endl;
 
 cin >> i;
 
 int arr[i];
 
 cout << "enter the value of yout arr\n";
 
 cin >> arr[i];
 
 int count = 0;
 
 for (int j = 0; j <= i; j++)
 {
 count += arr[j];
 }
 
 cout << count << endl;
 
 return 0;
}

• Remy Lebeau: Well, for starters, int arr[i]; is non-standard C++, you should be using std::vector instead. And cin >> arr[i]; is writing a single value out of bounds of the array. You are not actually filling the array with any values at all before entering your count loop. Also, FYI, the standard C++ library has a function for summing the values of a range, such as from an array: std::accumulate()
• Andreas Wenzel: What do you expect the line cin >> arr[i]; to do? Do you expect it to read several numbers and fill them into the array? If that is what you want, then you will need a loop instead.
• Swift - Friday Pie: You didn't input an array.. you had requested value for a single element arr[i] which is outside of array's bounds. Also j<=i is incorrect for same reason
• user4581301: Addendum: A <= in a for loop condition is so often wrong that if you see it when reviewing code, yours or anyone's, take a closer look at the loop because it's probably a bug.
• Abhishek Dutt: Please do read more about Array basics. You really need to do that.

Answer 1

The array int arr[i]; has only i elements: arr[0] to arr[i-1].

Therefore, the condition of the loop should be j < i, not j <= i.

cin >> arr[i]; is also wrong. You should use another loop to read i elements instead of readling only one to an out-of-range element like this.

#include <iostream>
#include <algorithm>
#include <vector>
#include <ctime>
#include <cstdlib>
#include <cctype>
using namespace std;
int main ()
{
 int i;
 cout << "enter the value of i" << endl;
 cin >> i;
 int arr[i];
 cout << "enter the value of yout arr\n";
 for (int j = 0; j < i; j++)
 {
 cin >> arr[j];
 }
 int count = 0;
 for (int j = 0; j < i; j++)
 {
 count += arr[j];
 }
 cout << count << endl;
 return 0;
}

Note that variable-length arrays (VLA) like int arr[i]; is not supported in the standard C++. You should use std::vector instead. You can do this by changing int arr[i]; to std::vector<int> arr(i); in this case.

Another choice is not using arrays and summing what are entered directly:

#include <iostream>
#include <algorithm>
#include <vector>
#include <ctime>
#include <cstdlib>
#include <cctype>
using namespace std;
int main ()
{
 int i;
 cout << "enter the value of i" << endl;
 cin >> i;
 cout << "enter the value of yout arr\n";
 int count = 0;
 for (int j = 0; j < i; j++)
 {
 int element;
 cin >> element;
 count += element;
 }
 cout << count << endl;
 return 0;
}