Language: C++

    #include<bits/stdc++.h>
#define mdw 1000000007
#define mdd 998244353
#define m18 1e18+1
#define ll long long 
#define forr(i,a,n) for(int i=a;i<n;i++)
#define forrll(i,a,n) for(long long i=a;i<n;i++)
#define forrlle(i,a,n) for(long long i=a;i<=n;i++)
#define forrllr(i,n,a) for(long long i=n-1;i>=a;i--)
#define pb push_back
#define vi vector<int>
#define mi unordered_map<int,int>
#define vll vector<long long>
#define vs vector<string>
#define mll unordered_map<long long,long long>
#define mp make_pair
#define gcd __gcd
#define umap unordered_map
// #define maxe *max_element
// #define mine *min_element
#define lb lower_bound
#define ub upper_bound
#define endll "\n"
#define N 500000
 using namespace std;

ll bpo(ll a,ll b) {
    if (b == 0)
        return 1;
    ll res = bpo(a, b / 2);
    if (b % 2)
        return res * res * a;
    else
        return res * res;
}

ll po(ll x,ll y,ll m){
    if(y==0){
        return 1;
    }
    ll temp=po(x,y/2,m);
    if(y%2==0){
        return ((temp%m)*(temp%m))%m;
    }else{
        return (((x%m)*(temp%m))%m*(temp)%m)%m;
    }
    
}

ll modinverse(ll a,ll m){
    return po(a,m-2,m);
}

ll myncr(int n, int r, int p) 
{ 
   if (r==0) 
      return 1;  
    ll fac[n+1]; 
    fac[0] = 1; 
    for (ll i=1 ; i<=n; i++) 
        fac[i] = fac[i-1]*i%p; 
  
    return (fac[n]* modinverse(fac[r], p) % p * 
            modinverse(fac[n-r], p) % p) % p; 
}

ll lcm(ll a, ll b){ 
    return (a*b)/(gcd(a, b));
}
ll max(ll a, ll b){
  if (a > b)
    return a;
  return b;
}
ll min(ll a, ll b){
  if (a < b)
    return a;
  return b;
}

bool comp(pair<ll,ll> a,pair<ll,ll> b){
    return a.second>b.second;
}

bool comp2(ll a,ll b){
    return a>b;
}


vector<int> parent(N), siz(N);
int find_set(int v) {
    if (v == parent[v])
        return v;
    return parent[v] = find_set(parent[v]);
}

void make_set(int v) {
    parent[v] = v;
    siz[v] = 1;
}

void union_sets(int a, int b) {
    a = find_set(a);
    b = find_set(b);
    if (a != b) {
        if (siz[a] < siz[b])
            swap(a, b);
        parent[b] = a;
        siz[a] += siz[b];
    }
}

ll bin(string s){
    reverse(s.begin(),s.end());
    ll n=0,k=1;
    forrll(i,0,s.size()){
        n+=(k*(s[i]-48));
        k*=2;
    }
    return n;
}

bool isv(ll a,ll b,ll n){
    return a>=0&&a<n&&b>=0&&b<n;
}


bool compp(pair<ll,ll>a,pair<ll,ll>b){
    if(a.first!=b.first)return a.first<b.first;
    else return a.second>b.second;
}

bool compi(ll a,ll b){
    return a>b;
}

bool isperfect(ll n){
    if(n<0) return false;
    ll a=(int)sqrt(n);
    return a*a==n;
}

#define PI 3.14159265358979323846

bool isPrime(int x) {
    for (int d = 2; d * d <= x; d++) {
        if (x % d == 0)
            return false;
    }
    return true;
}

bool compg(ll a,ll b){
    return a>b;
}



int main()
{
   
    ios::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
    
    ll t,q;
    cin>>t;
    //   t=1;
    
    while(t--){

      string s,t;
        cin>>s>>t;
        ll c=0;
        forrll(i,0,n){if(s[i]!=t[i])c++;}
        cout<<c<<endll;
        
   }
}


Compiler output:
a.cc: In function 'int main()':
a.cc:175:20: error: 'n' was not declared in this scope
  175 |         forrll(i,0,n){if(s[i]!=t[i])c++;}
      |                    ^
a.cc:7:43: note: in definition of macro 'forrll'
    7 | #define forrll(i,a,n) for(long long i=a;i<n;i++)
      |                                           ^