Language: C

#include <iostream>
#include <string>
#include <algorithm>
#include <vector>
#include <cmath>
#include <numeric>
#include <set>
#include <list>
#include <map>
#include <unordered_map>
#include<queue>
#include <stack>
#include<iomanip>
#include <math.h>
#include <functional>
 
const long long int INF = 1 << 60;
const long long MOD = 1000000007;
const double pi = 3.141592;
using namespace std;
using Graph = vector<vector<int>>;
 
template<class T> bool chmin(T &a, T b) { if (a > b) { a = b; return 1; }return 0; }
template<class T> bool chmax(T &a, T b) { if (a < b) { a = b; return 1; }return 0; }
template<class T, class U> using P = pair<T, U>;
 
vector<int> seen(50,-1);
int counter_for_dfs = 0;
void dfs(Graph &G, int v) {
	seen[v] = counter_for_dfs;
	counter_for_dfs++;
	for (auto v_next : G[v]) {
		if (seen[v_next]>=0)continue;
 
		dfs(G, v_next);
	}
}
 
void bfs(Graph &G) {
	vector<int> dist(G.size(), -1);
	queue<int> que;
	
	dist[0] = 0;
	que.push(0);
	while (!que.empty()) {
		int v = que.front();
		que.pop();
 
		for (int g : G[v]) {
			if (dist[g] != -1)continue;
			dist[g] = dist[v] + 1;
			que.push(g);
		}
	}
	for (auto i : dist) {
		cout << i << " ";
	}
}
 
int counter[200005] = {};
void bfs2(Graph &G,int p,int x) {
	vector<int> dist(G.size() , -1);
	queue<int> que;
	
	dist[p] = 0;
	que.push(p);
	while (!que.empty()) {
		int v = que.front();
		que.pop();
 
		for (int g : G[v]) {
			if (dist[g] != -1)continue;
			dist[g] = dist[v] + 1;
			que.push(g);
			counter[g] += x;
		}
	}
}
long long int gcd(long long int a, long long int b) {
	long long int c = std::min(a, b);
	a = std::max(a, b);
	b = c;
	while (true) {
		c = a % b;
		a = b;
		b = c;
		if (c == 0)break;
	}
	return a;
}
long long int factorial(int start,int end = 1) {
	if (start == 0)return 1;
	return start == end ? end : start * factorial(start - 1,end);
}
long long int npr(int n, int r) {
	return factorial(n) / factorial(n - r);
}
 
long long int ncr(int n, int r) {
	return npr(n, r) / factorial(r);
}
 
static unsigned long _XorShift_x = 123456789;
static unsigned long _XorShift_y = 362436069;
static unsigned long _XorShift_z = 521288629;
static unsigned long _XorShift_w = 88675123;
double XorShift() {
	unsigned long t = (_XorShift_x ^ (_XorShift_x << 11));
	_XorShift_x = _XorShift_y; _XorShift_y = _XorShift_z; _XorShift_z = _XorShift_w;
	_XorShift_w = (_XorShift_w ^ (_XorShift_w >> 19)) ^ (t ^ (t >> 8));
	double res = ((_XorShift_x + 0.5) / 4294967296.0 + _XorShift_w) / 4294967296.0;
	return res;
}
 
//double SAniealing() {
//	double x;
//	double T;
//	double f, fd;
//	srand((unsigned int)time(NULL));
//	x = (rand() + 0.5) / RAND_MAX;
//	T = 100;
//	f = x * x * x * x  + x * (x-2) -1;
//	double p = 0;
//	while (T > 0.01) {
//		int i = XorShift() > 0.5 ? 1 : -1;
//		double tempx;
//		if (T > 0.03) {
//			tempx = x + i * XorShift();
//		}
//		else {
//			tempx = x + i * XorShift() * 0.001;
//		}
//		fd = tempx * tempx * tempx * tempx + tempx * (tempx-2) - 1 ;
//		if (fd < f) {
//			f = fd;
//			x = tempx;
//		}
//		else {
//			p = exp(-(fd - f) / T);
//			if (p > 0.5) {
//				f = fd;
//				x = tempx;
//			}
//		}
//		T *= 0.9999;
//		
//		//cout << "T=" << T << ":p=" << p <<":f - fd ="<<f - fd<<":x=" << x << endl;
//	}
//
//	return x;
//}
 
int main(){
 
	char alpha; cin >> alpha;
	char rslt;

	if (isupper(alpha)) {
		rslt = 'A';
	}
	else {
		rslt = 'a';
	}
	cout << rslt;

	return 0;
}

Compiler output:
main.c:1:10: fatal error: iostream: No such file or directory
    1 | #include <iostream>
      |          ^~~~~~~~~~
compilation terminated.