Language: C++

#include<bits/stdc++.h>
#define mod 1000000007
#define pb push_back
#define ff first
#define ss second
#define ii pair<int,int>
#define vi vector<int>

#define mii map<int,int>
#define int long long
#define inf 2000000000000000000
#define re(i,x,n) for(i=x;i<=n;i++)
typedef long long ll;
using namespace std;
void c_p_c()
{
	ios_base::sync_with_stdio(0);
	cin.tie(0);
	cout.tie(0);
#ifndef  ONLINE_JUDGE
	freopen("input.txt", "r", stdin);
	freopen("output.txt", "w", stdout);
#endif
}
struct edge
{
	int a;
	int b;
	int w;
};
edge ar[100000];
int par[10001];
bool comp(edge a, edge b)
{
	if (a.w < b.w)
		return true;
	else
		return false;
}
int find(int a)
{
	if (par[a] == -1)
		return a;
	else
		return par[a] = find(par[a]);
}
void merge(int a, int b)
{
	par[a] = b;
}
void Sieve(int  n)
{
	int i;
	bool primes[n + 1];
	memset(primes, true, sizeof(primes));
	int j;
	for (i = 2; i * i <= n; i++)
	{
		if (primes[i])
		{
			for (j = i * i; j <= n; j += i)
				primes[j] = false;
		}
	}
	int a[n + 1];
	int k = -1;
	for (i = 2; i <= n; i++)
		if (primes[i]) {
			//cout << i << " ";
			a[++k] = i;
		}
//	cout << endl;
	int count = 0;


	int r = 0;
	bool be = false;
	for (i = 6; i <= n; i++)
	{
		for (j = 0; j <= k; j++)
		{
			if (i % a[j] == 0)
				count++;
			if (count == 2) {

				be = true;
				break;
			}
		}
		if (be) {
			r++;

			be = false;
		}
		count = 0;
	}
	// cout << endl;
	cout << r << endl;

}
void SieveOfEratosthenes(int n, bool prime[],
                         bool primesquare[], int a[])
{
	// Create a boolean array "prime[0..n]" and
	// initialize all entries it as true. A value
	// in prime[i] will finally be false if i is
	// Not a prime, else true.
	for (int i = 2; i <= n; i++)
		prime[i] = true;

	// Create a boolean array "primesquare[0..n*n+1]"
	// and initialize all entries it as false. A value
	// in squareprime[i] will finally be true if i is
	// square of prime, else false.
	for (int i = 0; i <= (n * n + 1); i++)
		primesquare[i] = false;

	// 1 is not a prime number
	prime[1] = false;

	for (int p = 2; p * p <= n; p++) {
		// If prime[p] is not changed, then
		// it is a prime
		if (prime[p] == true) {
			// Update all multiples of p
			for (int i = p * 2; i <= n; i += p)
				prime[i] = false;
		}
	}

	int j = 0;
	for (int p = 2; p <= n; p++) {
		if (prime[p]) {
			// Storing primes in an array
			a[j] = p;

			// Update value in primesquare[p*p],
			// if p is prime.
			primesquare[p * p] = true;
			j++;
		}
	}
}

// Function to count divisors
int countDivisors(int n)
{
	// If number is 1, then it will have only 1
	// as a factor. So, total factors will be 1.
	if (n == 1)
		return 1;

	bool prime[n + 1], primesquare[n * n + 1];

	int a[n]; // for storing primes upto n

	// Calling SieveOfEratosthenes to store prime
	// factors of n and to store square of prime
	// factors of n
	SieveOfEratosthenes(n, prime, primesquare, a);

	// ans will contain total number of distinct
	// divisors
	int ans = 1;

	// Loop for counting factors of n
	for (int i = 0;; i++) {
		// a[i] is not less than cube root n
		if (a[i] * a[i] * a[i] > n)
			break;

		// Calculating power of a[i] in n.
		int cnt = 1; // cnt is power of prime a[i] in n.
		while (n % a[i] == 0) // if a[i] is a factor of n
		{
			n = n / a[i];
			cnt = cnt + 1; // incrementing power
		}

		// Calculating number of divisors
		// If n = a^p * b^q then total divisors of n
		// are (p+1)*(q+1)
		ans = ans * cnt;
	}

	// if a[i] is greater than cube root of n

	// First case
	if (prime[n])
		ans = ans * 2;

	// Second case
	else if (primesquare[n])
		ans = ans * 3;

	// Third casse
	else if (n != 1)
		ans = ans * 4;

	return ans; // Total divisors
}
int32_t main()
{

	//c_p_c();
	int n;
	cin >> n;
	int count = 0;
	int i;
	for (i = 1; i <= n; i++)
	{
		for (j = 1; j <= n; j++)
		{
			if (i % j == 0)
				count += i;
		}
	}
	cout << count;

}

Compiler output:
a.cc: In function 'int32_t main()':
a.cc:212:22: error: 'j' was not declared in this scope
  212 |                 for (j = 1; j <= n; j++)
      |                      ^