goorm 뱀이 지나간 자리, 피보나치 수열, 소수의 개수 구하기

#include <iostream>
using namespace std;
int main(void){
	int n, m;
	cin >> n >> m;
	int i=0;
	while(1){
		i++; //1
		if(i>n)
			break;
		for(int j = 0; j<m; j++)
			cout<<"#";
		cout<<endl;
		
        i++;
		if(i>n)
			break;
		for(int j=1; j<m; j++)
			cout<<".";
		cout<<"#"<<endl;
		
		i++;
		if(i>n)
			break;
		for(int j = 0; j<m;j++)
			cout<<"#";
		cout<<endl;
        
		i++;
		if(i>n)
			break;
		cout<<"#";
		for(int j=1; j<m; j++)
			cout<<".";
		cout<<endl;
	}
	return 0;
}

 

#include <iostream>
using namespace std;
int main(void) {
	int input;
	cin >> input;
	int a = 0;
	int b = 1;
	int c;
	int sum = 1;
	for(int i =1; i < input; i++){
		c = a + b;
		sum += c;
		a = b;
		b = c;
	}
	cout << sum;
	return 0;
}

 

#include <iostream>
using namespace std;
int main(void) {
	int n;
	cin >> n;
	int cnt=0;
	int sum;
	for(int i = 2; i <= n; i++){
		sum =0;
		for(int j = 2; j <i; j++){
			if(i%j==0)
				sum++;
		}
		if(sum==0)
				cnt++;
	}
	cout<<cnt;
	return 0;
}