A+B problem

#include <bits/stdc++.h>
using namespace std;

#define ll long long
const int N = 1010;

int RAND_1(ll a,ll b){
    ll n = a + b;
    return n;
}

int RAND_2(string a, string b, int n[500], int m[500], int ans[501]){
    for(int i = 0; i < a.size(); i++)
		n[i] = a[a.size() - i - 1] - '0';
	for(int i = 0; i < b.size(); i++)
		m[i] = b[b.size() - i - 1] - '0';
	int len_maxn = max(a.size(), b.size()) + 1;
	for(int i = 0; i < len_maxn; i++)
	{
		ans[i] = n[i] + m[i] + ans[i];
		if(ans[i] > 9)
		{
			ans[i + 1]++;
			ans[i] = ans[i] % 10;
		}
	}
	while(ans[len_maxn - 1] == 0 && len_maxn > 0) len_maxn--;
	for(int i = len_maxn - 1; i >= 0; i--) cout << ans[i];
	return 0;
}

int RAND_3(ll a, ll b){
	ll ans = 0;
	for(int i = 0; i < a; i ++ ) {
		ans ++;
	}
	for(int i = 0; i < b; i ++ ) {
		ans ++;
	}
	return ans;
}

int n[1010], m[1010],c[1010];
int main(){
	srand(time(0));
    ll a , b;
    string z , y;
    int x;
    x = 1 + rand() % 3;
    if(x == 1){
    	cin >> a >> b;
    	int ans = RAND_1(a,b);
    	cout << ans;
	}
    if(x == 2){
    	cin >> z >> y;
    	RAND_2(z , y , n , m, c);
	}
	if(x == 3){
		cin >> a >> b;
		int ans = RAND_3(a, b);
		cout << ans;
	}
    return 0;
}