//#include <iostream>
//#include <cstdint>
//#include <time.h>
#include <bits/stdc++.h>
using namespace std;

#define ll long long
#define ld long double

const int limit = 1e8 + 8;

namespace bitsetSieve {
	uint64_t p[limit / 64 + 11];

	bool test(int idx) {
		return (p[idx / 64] & (1ULL << (idx % 64))) == 0;
	}

	void mark(int idx) {
		p[idx / 64] |= (1ULL << (idx % 64));
	}

	void sieve() {
		mark(0);
		mark(1);
		for (int i = 3; i * i < limit; i += 2) {
			if (test(i)) {
				for (int j = i * i; j < limit; j += i * 2) {
					mark(j);
				}
			}
		}
	}
}

namespace bitsetSieve2 {
	uint32_t p[limit / 32 + 11];

	bool test(int idx) {
		return (p[idx >> 5] & (1 << (idx % 32)));
	}

	void mark(int idx) {
		p[idx >> 5] &= ~(1 << (idx % 32));
	}

	void sieve() {
		const uint32_t bit1 = ~0;
		memset(p, bit1, sizeof p);
		p[0] = bit1 - 3;
		register uint32_t* pointer = bitsetSieve2::p;
		for (int i = 3; i * i < limit; i += 2) {
			register int i2 = i % 32;
			if(i2 == 1) {
				++pointer;
			}
			if ((*pointer) & (1 << i2)) {
				for (int j = i * i; j < limit; j += i * 2) {
					p[j >> 5] &= ~(1 << (j % 32));
				}
			}
		}
	}
}

namespace boolSieve {
	bool p[limit];
	
	void sieve() {
		memset(p, 1, sizeof p);
		p[0] = p[1] = 0;
		for (int i = 3; i * i < limit; i += 2) {
			if (p[i]) {
				for (int j = i * i; j < limit; j += i * 2) {
					p[j] = 0;
				}
			}
		}
	}
}


int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(NULL);
	cout.tie(NULL);

	clock_t start = clock();
	boolSieve::sieve();
	cout << "bool sieve: " << clock() - start <<"ms"<< endl;

	start = clock();
	bitsetSieve2::sieve();
	cout << "bitset sieve: " << clock() - start <<"ms"<< endl;

	for(register int i=0; i<limit; ++i) {
		if(boolSieve::p[i] != bitsetSieve2::test(i)) {
			cout << i << " - Error! " << endl;
			break;
		}
	}

	return 0;
}

C++ Online Compiler

Write, Run & Share C++ code online using OneCompiler's C++ online compiler for free. It's one of the robust, feature-rich online compilers for C++ language, running on the latest version 17. Getting started with the OneCompiler's C++ compiler is simple and pretty fast. The editor shows sample boilerplate code when you choose language as C++ and start coding!

Read inputs from stdin

OneCompiler's C++ online compiler supports stdin and users can give inputs to programs using the STDIN textbox under the I/O tab. Following is a sample program which takes name as input and print your name with hello.

#include <iostream>
#include <string>
using namespace std;

int main() 
{
    string name;
    cout << "Enter name:";
    getline (cin, name);
    cout << "Hello " << name;
    return 0;
}

About C++

C++ is a widely used middle-level programming language.

  • Supports different platforms like Windows, various Linux flavours, MacOS etc
  • C++ supports OOPS concepts like Inheritance, Polymorphism, Encapsulation and Abstraction.
  • Case-sensitive
  • C++ is a compiler based language
  • C++ supports structured programming language
  • C++ provides alot of inbuilt functions and also supports dynamic memory allocation.
  • Like C, C++ also allows you to play with memory using Pointers.

Syntax help

Loops

1. If-Else:

When ever you want to perform a set of operations based on a condition If-Else is used.

if(conditional-expression) {
   //code
}
else {
   //code
}

You can also use if-else for nested Ifs and If-Else-If ladder when multiple conditions are to be performed on a single variable.

2. Switch:

Switch is an alternative to If-Else-If ladder.

switch(conditional-expression){    
case value1:    
 // code    
 break;  // optional  
case value2:    
 // code    
 break;  // optional  
......    
    
default:     
 code to be executed when all the above cases are not matched;    
}

3. For:

For loop is used to iterate a set of statements based on a condition.

for(Initialization; Condition; Increment/decrement){  
  //code  
}

4. While:

While is also used to iterate a set of statements based on a condition. Usually while is preferred when number of iterations are not known in advance.

while (condition) {  
// code 
}

5. Do-While:

Do-while is also used to iterate a set of statements based on a condition. It is mostly used when you need to execute the statements atleast once.

do {  
 // code 
} while (condition);

Functions

Function is a sub-routine which contains set of statements. Usually functions are written when multiple calls are required to same set of statements which increases re-usuability and modularity. Function gets run only when it is called.

How to declare a Function:

return_type function_name(parameters);

How to call a Function:

function_name (parameters)

How to define a Function:

return_type function_name(parameters) {  
 // code
}