Language: C++

using System;


class NumberTheory {
    bool isFact;
    long[] fact;
    public NumberTheory(){
        isFact = false;
    }
    
    public void FactTable(long n, long m){
        isFact = true;
        fact = new long[n+1];
        fact[0] = 1;
        for(long i=1;i<n+1;i++){
            fact[i] = (fact[i-1]*i)%m;
        }
    }
    
    public long GetFact(long n){
        if(isFact && -1<n && n<=fact.Length){
            return fact[n];
        } else {
            return -1;
        }
    }
    
    public long Mod_fact(long n, long p, out long e){
        e = 0;
        if(!isFact){
            Console.WriteLine("Error:FactTable is not created!!");
            return -1;
        }
        if(n==0) return 1;
        long res = Mod_fact(n/p,p, out e);
        e += n/p;
        
        if(n/p%2!=0) return res * (p-fact[n%p])%p;
        return res*fact[n%p]%p;
    }
    
    public long Mod_cmb(long n, long k, long p){
        if(n<0||k<0||n<k) return 0;
        long e1,e2,e3;
        long a1 = Mod_fact(n,p, out e1),a2 = Mod_fact(k,p, out e2),a3 = Mod_fact(n-k,p, out e3);
        if(e1>e2+e3) return 0;
        return a1 * Mod_inverse(a2*a3%p, p)%p;
    }
    
    public long Extgcd(long a, long b, out long x, out long y){
        long d = a;
        if(b!=0){
            d = Extgcd(b,a%b, out y, out x);
            y -= (a/b)*x;
        } else {
            x = 1; y = 0;
        }
        return d;
    }
    
    public long Mod_inverse(long a, long m){
        long x,y;
        Extgcd(a,m, out x, out y);
        return (m+x%m)%m;
    }
    
}

public class Program{
    static void Main(string[] args){
        long N = 1000000007;
        NumberTheory nt = new  NumberTheory();
        string[]  str = Console.ReadLine().Split(' ');
        long H = long.Parse(str[0]);
        long W = long.Parse(str[1]);
        nt.FactTable(H+W,N);
        long A = long.Parse(str[2]);
        long B = long.Parse(str[3]);
        long ans = 0;
        for(int i=1;i<H-A+1;i++){
            ans +=  nt.Mod_cmb(B+i-2,i-1,N) * nt.Mod_cmb(H+W-i-B-1,H-i,N) % N;
            ans = ans % N;
        }
        Console.WriteLine(ans);
    }
}

Compiler output:
a.cc:1:7: error: expected nested-name-specifier before 'System'
    1 | using System;
      |       ^~~~~~
a.cc:6:9: error: expected unqualified-id before '[' token
    6 |     long[] fact;
      |         ^
a.cc:7:11: error: expected ':' before 'NumberTheory'
    7 |     public NumberTheory(){
      |           ^~~~~~~~~~~~~
      |           :
a.cc:11:11: error: expected ':' before 'void'
   11 |     public void FactTable(long n, long m){
      |           ^~~~~
      |           :
a.cc:20:11: error: expected ':' before 'long'
   20 |     public long GetFact(long n){
      |           ^~~~~
      |           :
a.cc:28:11: error: expected ':' before 'long'
   28 |     public long Mod_fact(long n, long p, out long e){
      |           ^~~~~
      |           :
a.cc:28:42: error: 'out' has not been declared
   28 |     public long Mod_fact(long n, long p, out long e){
      |                                          ^~~
a.cc:42:11: error: expected ':' before 'long'
   42 |     public long Mod_cmb(long n, long k, long p){
      |           ^~~~~
      |           :
a.cc:50:11: error: expected ':' before 'long'
   50 |     public long Extgcd(long a, long b, out long x, out long y){
      |           ^~~~~
      |           :
a.cc:50:40: error: 'out' has not been declared
   50 |     public long Extgcd(long a, long b, out long x, out long y){
      |                                        ^~~
a.cc:50:52: error: 'out' has not been declared
   50 |     public long Extgcd(long a, long b, out long x, out long y){
      |                                                    ^~~
a.cc:61:11: error: expected ':' before 'long'
   61 |     public long Mod_inverse(long a, long m){
      |           ^~~~~
      |           :
a.cc:67:2: error: expected ';' after class definition
   67 | }
      |  ^
      |  ;
a.cc: In member function 'void NumberTheory::FactTable(long int, long int)':
a.cc:13:9: error: 'fact' was not declared in this scope; did you mean 'isFact'?
   13 |         fact = new long[n+1];
      |         ^~~~
      |         isFact
a.cc: In member function 'long int NumberTheory::GetFact(long int)':
a.cc:21:33: error: 'fact' was not declared in this scope; did you mean 'isFact'?
   21 |         if(isFact && -1<n && n<=fact.Length){
      |                                 ^~~~
      |                                 isFact
a.cc: In member function 'long int NumberTheory::Mod_fact(long int, long int, long int)':
a.cc:31:13: error: 'Console' was not declared in this scope
   31 |             Console.WriteLine("Error:FactTable is not created!!");
      |             ^~~~~~~
a.cc:35:36: error: 'out' was not declared in this scope
   35 |         long res = Mod_fact(n/p,p, out e);
      |                                    ^~~
a.cc:38:38: error: 'fact' was not declared in this scope; did you mean 'isFact'?
   38 |         if(n/p%2!=0) return res * (p-fact[n%p])%p;
      |                                      ^~~~
      |                                      isFact
a.cc:39:20: error: 'fact' was not declared in this scope; did you mean 'isFact'?
   39 |         return res*fact[n%p]%p;
      |                    ^~~~
      |                    isFact
a.cc: In member function 'long int NumberTheory::Mod_cmb(long int, long int, long int)':
a.cc:45:33: error: 'out' was not declared in this scope
   45 |         long a1 = Mod_fact(n,p, out e1),a2 = Mod_fact(k,p, out e2),a3 = Mod_fact(n-k,p, out e3);
      |                                 ^~~
a.cc:47:33: error: 'a2' was not declared in this scope; did you mean 'a1'?
   47 |         return a1 * Mod_inverse(a2*a3%p, p)%p;
      |                                 ^~
      |                                 a1
a.cc:47:36: error: 'a3' was not declared in this scope; did you mean 'a1'?
   47 |         return a1 * Mod_inverse(a2*a3%p, p)%p;
      |                                    ^~
      |                                    a1
a.cc: In member function 'long int NumberTheory::Extgcd(long int, long int, long int, long int)':
a.cc:53:31: error: 'out' was not declared in this scope
   53 |             d = Extgcd(b,a%b, out y, out x);
      |                               ^~~
a.cc:53:42: error: expected ')' before 'x'
   53 |             d = Extgcd(b,a%b, out y, out x);
      |                                          ^
a.cc:53:23: note: to match this '('
   53 |             d = Extgcd(b,a%b, out y, out x);
      |                       ^
a.cc: In member function 'long int NumberTheory::Mod_inverse(long int, long int)':
a.cc:63:21: error: 'out' was not declared in this scope
   63 |         Extgcd(a,m, out x, out y);
      |                     ^~~
a.cc:63:32: error: expected ')' before 'y'
   63 |         Extgcd(a,m, out x, out y);
      |                                ^
a.cc:63:15: note: to match this '('
   63 |         Extgcd(a,m, out x, out y);
      |               ^
a.cc: At global scope:
a.cc:69:1: error: expected unqualified-id before 'public'
   69 | public class Program{
      | ^~~~~~