Language: C++

#include "bits/stdc++.h"

using namespace std;
  
typedef unsigned long long ULL;
typedef long long LL;
typedef pair<int, int> pr;
typedef pair<LL, LL> lpr;
typedef pair<double, double> dpr;
typedef pair<long double, long double> ldpr;
typedef double db;
typedef long double ld;
typedef complex<double> cp;
// typedef pair<ld,ld> pt;
  
#define dbgs(x) #x << " = " << x
#define dbgs2(x, y) dbgs(x) << ", " << dbgs(y)
#define dbgs3(x, y, z) dbgs2(x, y) << ", " << dbgs(z)
#define dbgs4(w, x, y, z) dbgs3(w, x, y) << ", " << dbgs(z)
 
#define mst(s, x) memset(s, x, sizeof(s))
#define fi first
#define se second
#define pb push_back
#define pf push_front
#define ppb pop_back
#define ppf pop_front
#define mp make_pair
#define all(x) x.begin(), x.end()
#define unq(x) x.erase(unique(x.begin(), x.end()), x.end())
#define rg register
#define fp(i, a, b) for (rg int i = (a), I = (b) + 1; i < I; ++i)
#define fd(i, a, b) for (rg int i = (a), I = (b)-1; i > I; --i)
#define ub upper_bound
#define lb lower_bound
#define bitcount __builtin_popcount
#define sqr(x) ((x)*(x))
 
#define go(u) for (rg int i = pre[u], v = e[i].v; i; i = e[i].next, v = e[i].v)
#define gow(u) for (rg LL i = pre[u], v = e[i].v, w = e[i].w; i; i = e[i].next, v = e[i].v, w = e[i].w)
#define EDGE(N,M) struct edge{int u,v,w,next;}e[M];int pre[N],edge_cnt=0;void addedge(int u,int v,int w=0){edge_cnt=edge_cnt+1,e[edge_cnt].u=u,e[edge_cnt].v=v,e[edge_cnt].w=w,e[edge_cnt].next=pre[u],pre[u]=edge_cnt;}
#define CLEAR_EDGE(N) {edge_cnt=0,memset(pre,0,sizeof(int)*(N+1));}
 
#define MAXSIZE (1 << 20)
#define isdigit(x) (x >= '0' && x <= '9')
 
#define MC int _CASE;scanf("%d",&_CASE);fp(case_num,1,_CASE)
  
const int next_x[8] = {0, 1, -1, 0, 1, 1, -1, -1};
const int next_y[8] = {1, 0, 0, -1, 1, -1, -1, 1};
const int inf = 1e9+5;//7;
const LL linf = 1e18;
const double PI = acos(-1.0);
  
const int MAXN = 1e5+5;
const int N    = 1e6+5;

#define mid ((l+r)/2)
#define ls ((cnt<<1))
#define rs ((cnt<<1|1))
  
/*----------head----------*/

int n,m,a,b,c;
int a[MAXN];
int work()
{
    int l,r,d;
    int ans=0;
    cin >> l >> r >> d;
    fp(i,l,r)
    {
        ans+=(i%d==0);
    }
    cout << ans << endl;
    return 0;
}


// 小数 二分/三分 注意break条件
// 浮点运算 sqrt(a^2-b^2) 可用 sqrt(a+b)*sqrt(a-b) 代替，避免精度问题
// long double -> %Lf 别用C11 (C14/16)
// 控制位数 cout << setprecision(10) << ans;
// reverse vector 注意判空 不然会re
// 分块注意维护块上标记 来更新块内数组a[]
// vector+lower_bound常数 < map/set
// map.find不会创建新元素 map[]会 注意空间
// 别对指针用memset
// 用位运算表示2^n注意加LL  1LL<<20
// 注意递归爆栈
// 注意边界
// 注意memset 多组样例会T
  
//#define ONLINE_JUDGE

int main()
{
    // ios::sync_with_stdio(false);
    // cin.tie(0);
#ifdef ONLINE_JUDGE
    //freopen("triatrip.in", "r",stdin );
    //freopen("triatrip.out","w",stdout);
#endif // ONLINE_JUDGE
#ifndef ONLINE_JUDGE
    int size = 512 << 20; // 512MB  
    char *p = (char*)malloc(size) + size;  
    __asm__("movl %0, %%esp\n" :: "r"(p));
    freopen("input.txt", "r", stdin);
    // freopen("output.txt", "w", stdout);
#endif
    // make();
    work();
#ifndef ONLINE_JUDGE
    cout << "time:" << clock() << "ms" << endl;
    freopen("CON", "r", stdin);
    freopen("CON", "w", stdout);
    system("pause");
    fflush(stdout);
#endif
    return 0;
}

Compiler output:
a.cc:65:5: error: conflicting declaration 'int a [100005]'
   65 | int a[MAXN];
      |     ^
a.cc:64:9: note: previous declaration as 'int a'
   64 | int n,m,a,b,c;
      |         ^
a.cc: In function 'int work()':
a.cc:71:8: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   71 |     fp(i,l,r)
      |        ^
a.cc:32:33: note: in definition of macro 'fp'
   32 | #define fp(i, a, b) for (rg int i = (a), I = (b) + 1; i < I; ++i)
      |                                 ^
a.cc:32:42: warning: ISO C++17 does not allow 'register' storage class specifier [-Wregister]
   32 | #define fp(i, a, b) for (rg int i = (a), I = (b) + 1; i < I; ++i)
      |                                          ^
a.cc:71:5: note: in expansion of macro 'fp'
   71 |     fp(i,l,r)
      |     ^~