#include <cstdint>
#include <stdio.h>
#include <time.h>

const int limit = 1e8 + 8;
uint64_t p[limit / 64 + 11];

bool test(int idx) {
	return (p[idx >> 6] & (1ULL<<(idx & 63))) == 0;
}

void mark(int idx) {
	p[idx >> 6] |= (1ULL<<(idx & 63));
}

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);
			}
		}
	}
}


bool p4[limit + 11] = {false};

bool test4(int idx) {
	return p4[idx] == false;
}

void mark4(int idx) {
	p4[idx] = true;
}

void sieve4() {
	mark4(false);
	mark4(true);
	for (int i = 3; i * i < limit; i += 2) {
		if (test4(i)) {
			for (int j = i * i; j < limit; j += i * 2) {
				mark4(j);
			}
		}
	}
}

int main() {
	const int MAX_TRY = 1;
	clock_t start, end;
	start = clock();
	for(int i=0; i<MAX_TRY; ++i) {
		sieve4();
	}
	end = clock();
	printf("sieve bool: %ld ms\n", end - start);

	start = clock();
	for(int i=0; i<MAX_TRY; ++i) {
		sieve();
	}
	end = clock();
	printf("sieve: %ld ms\n", end - start);
	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
}