Language: C++

//include
//------------------------------------------
#include <vector>
#include <list>
#include <map>
#include <set>
#include <deque>
#include <stack>
#include <bitset>
#include <algorithm>
#include <functional>
#include <numeric>
#include <utility>
#include <sstream>
#include <iostream>
#include <iomanip>
#include <cstdio>
#include <cmath>
#include <cstdlib>
#include <cctype>
#include <string>
#include <cstring>
#include <ctime>

using namespace std;

//conversion
//------------------------------------------
inline int toInt(string s) {int v; istringstream sin(s);sin>>v;return v;}
template<class T> inline string toString(T x) {ostringstream sout;sout<<x;return sout.str();}

//math
//-------------------------------------------
template<class T> inline T sqr(T x) {return x*x;}

//typedef
//------------------------------------------
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<string> VS;
typedef pair<int, int> PII;
typedef long long LL;

//container util
//------------------------------------------
#define ALL(a)  (a).begin(),(a).end()
#define RALL(a) (a).rbegin(), (a).rend()
#define PB push_back
#define MP make_pair
#define SZ(a) int((a).size())
#define EACH(i,c) for(typeof((c).begin()) i=(c).begin(); i!=(c).end(); ++i)
#define EXIST(s,e) ((s).find(e)!=(s).end())
#define SORT(c) sort((c).begin(),(c).end())

//repetition
//------------------------------------------
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define REP(i,n)  FOR(i,0,n)

//constant
//--------------------------------------------
const double EPS = 1e-10;
const double PI  = acos(-1.0);

//clear memory
#define CLR(a) memset((a), 0 ,sizeof(a))

//debug
#define dump(x)  cerr << #x << " = " << (x) << endl;
#define debug(x) cerr << #x << " = " << (x) << " (L" << __LINE__ << ")" << " " << __FILE__ << endl;

int main(){
    char S;
    char V;
    cin >> S;
    if(S=="Sunnny") V = "Cloudy";
    if(S=="Cloudy") V = "Rainy";
    if(S=="Rainy") V = "Sunny";

    cout << V << endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:76:9: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   76 |     if(S=="Sunnny") V = "Cloudy";
      |        ~^~~~~~~~~~
a.cc:76:25: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   76 |     if(S=="Sunnny") V = "Cloudy";
      |                         ^~~~~~~~
      |                         |
      |                         const char*
a.cc:77:9: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   77 |     if(S=="Cloudy") V = "Rainy";
      |        ~^~~~~~~~~~
a.cc:77:25: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   77 |     if(S=="Cloudy") V = "Rainy";
      |                         ^~~~~~~
      |                         |
      |                         const char*
a.cc:78:9: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
   78 |     if(S=="Rainy") V = "Sunny";
      |        ~^~~~~~~~~
a.cc:78:24: error: invalid conversion from 'const char*' to 'char' [-fpermissive]
   78 |     if(S=="Rainy") V = "Sunny";
      |                        ^~~~~~~
      |                        |
      |                        const char*