# Program to print prime numbers from 1 to N.

• Difficulty Level : Easy
• Last Updated : 14 Sep, 2022

Given a number N, the task is to print the prime numbers from 1 to N.
Examples:

```Input: N = 10
Output: 2, 3, 5, 7

Input: N = 5
Output: 2, 3, 5 ```

Algorithm:

• First, take the number N as input.
• Then use a for loop to iterate the numbers from 1 to N
• Then check for each number to be a prime number. If it is a prime number, print it.

Approach 1:  Now, according to formal definition, a number ‘n’ is prime if it is not divisible by any number other than 1 and n. In other words a number is prime if it is not divisible by any number from 2 to n-1.

Below is the implementation of the above approach:

## C++

 `// C++ program to display Prime numbers till N ` `#include ` `using` `namespace` `std; ` ` `  `// function to check if a given number is prime ` `bool` `isPrime(``int` `n) ` `{ ` `    ``// since 0 and 1 is not prime return false. ` `    ``if` `(n == 1 || n == 0) ` `        ``return` `false``; ` ` `  `    ``// Run a loop from 2 to n-1 ` `    ``for` `(``int` `i = 2; i < n; i++) { ` `        ``// if the number is divisible by i, then n is not a ` `        ``// prime number. ` `        ``if` `(n % i == 0) ` `            ``return` `false``; ` `    ``} ` `    ``// otherwise, n is prime number. ` `    ``return` `true``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `N = 100; ` ` `  `    ``// check for every number from 1 to N ` `    ``for` `(``int` `i = 1; i <= N; i++) { ` `        ``// check if current number is prime ` `        ``if` `(isPrime(i)) ` `            ``cout << i << ``" "``; ` `    ``} ` ` `  `    ``return` `0; ` `} `

## C

 `// C program to display Prime numbers till N ` `#include ` `#include ` ` `  `// function to check if a given number is prime ` `bool` `isPrime(``int` `n) ` `{ ` `    ``// since 0 and 1 is not prime return false. ` `    ``if` `(n == 1 || n == 0) ` `        ``return` `false``; ` ` `  `    ``// Run a loop from 2 to n-1 ` `    ``for` `(``int` `i = 2; i < n; i++) { ` `        ``// if the number is divisible by i, then n is not a ` `        ``// prime number. ` `        ``if` `(n % i == 0) ` `            ``return` `false``; ` `    ``} ` `    ``// otherwise, n is prime number. ` `    ``return` `true``; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `N = 100; ` ` `  `    ``// check for every number from 1 to N ` `    ``for` `(``int` `i = 1; i <= N; i++) { ` `        ``// check if current number is prime ` `        ``if` `(isPrime(i)) ` `            ``printf``(``"%d "``, i); ` `    ``} ` ` `  `    ``return` `0; ` `} ` ` `  `// This code is contributed by Sania Kumari Gupta`

## Java

 `// Java program to display Prime numbers till N ` `class` `GFG  ` `{ ` `      ``//function to check if a given number is prime ` `     ``static` `boolean` `isPrime(``int` `n){ ` `          ``//since 0 and 1 is not prime return false. ` `          ``if``(n==``1``||n==``0``)``return` `false``; ` `   `  `          ``//Run a loop from 2 to n-1 ` `          ``for``(``int` `i=``2``; i

## Python3

 `# Python3 program to display Prime numbers till N ` ` `  `#function to check if a given number is prime ` `def` `isPrime(n): ` `  ``#since 0 and 1 is not prime return false. ` `  ``if``(n``=``=``1` `or` `n``=``=``0``): ` `    ``return` `False` `   `  `  ``#Run a loop from 2 to n-1 ` `  ``for` `i ``in` `range``(``2``,n): ` `    ``#if the number is divisible by i, then n is not a prime number. ` `    ``if``(n``%``i``=``=``0``): ` `      ``return` `False` `   `  `  ``#otherwise, n is prime number. ` `  ``return` `True` ` `  ` `  ` `  `# Driver code ` `N ``=` `100``; ` `#check for every number from 1 to N ` `for` `i ``in` `range``(``1``,N``+``1``): ` `  ``#check if current number is prime ` `  ``if``(isPrime(i)): ` `    ``print``(i,end``=``" "``) `

## C#

 `// C# program to display Prime numbers till N ` `using` `System; ` `     `  `class` `GFG  ` `{ ` `   `  `     ``//function to check if a given number is prime ` `     ``static` `bool` `isPrime(``int` `n){ ` `        ``//since 0 and 1 is not prime return false. ` `        ``if``(n==1||n==0) ``return` `false``; ` ` `  `        ``//Run a loop from 2 to n-1 ` `        ``for``(``int` `i=2; i

## Javascript

 ``

Output

`2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 `

Time Complexity: O(N^2),

Auxiliary Space: O(1)

Approach 2:  For checking if a number is prime or not do we really need to iterate through all the number from 2 to n-1? We already know that a number ‘n’ cannot be divided by any number greater than ‘n/2’. So, according to this logic we only need to iterate through 2 to n/2 since number greater than n/2 cannot divide n.

## C++

 `// C++ program to display Prime numbers till N ` `#include ` `using` `namespace` `std; ` ` `  `//function to check if a given number is prime ` `bool` `isPrime(``int` `n){ ` `    ``//since 0 and 1 is not prime return false. ` `    ``if``(n==1||n==0) ``return` `false``; ` ` `  `    ``//Run a loop from 2 to n/2. ` `    ``for``(``int` `i=2; i<=n/2; i++) { ` `          ``// if the number is divisible by i, then n is not a prime number. ` `          ``if``(n%i==0) ``return` `false``; ` `    ``} ` `    ``//otherwise, n is prime number. ` `    ``return` `true``; ` `} ` ` `  ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `N = 100; ` ` `  `    ``//check for every number from 1 to N ` `      ``for``(``int` `i=1; i<=N; i++){ ` `        ``//check if current number is prime ` `        ``if``(isPrime(i)) { ` `          ``cout << i << ``" "``; ` `        ``} ` `    ``} ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to display  ` `// Prime numbers till N ` `class` `GFG  ` `{ ` `     ``//function to check if a given number is prime ` `     ``static` `boolean` `isPrime(``int` `n){ ` `          ``//since 0 and 1 is not prime return false. ` `          ``if``(n==``1``||n==``0``) ``return` `false``; ` ` `  `        ``//Run a loop from 2 to n-1 ` `        ``for``(``int` `i=``2``; i<=n/``2``; i++){ ` `            ``// if the number is divisible by i, then n is not a prime number. ` `            ``if``(n%i==``0``)``return` `false``; ` `        ``} ` `        ``//otherwise, n is prime number. ` `        ``return` `true``; ` `    ``} ` `     `  ` `  `    ``// Driver code  ` `    ``public` `static` `void` `main (String[] args)  ` `    ``{  ` `        ``int` `N = ``100``;  ` `        ``//check for every number from 1 to N ` `        ``for``(``int` `i=``1``; i<=N; i++){ ` `            ``//check if current number is prime ` `            ``if``(isPrime(i)) { ` `              ``System.out.print(i + ``" "``); ` `            ``} ` `        ``} ` ` `  `    ``} ` `} `

## Python3

 `# Python3 program to display Prime numbers till N ` ` `  `#function to check if a given number is prime ` `def` `isPrime(n): ` `  ``#since 0 and 1 is not prime return false. ` `  ``if``(n``=``=``1` `or` `n``=``=``0``): ` `    ``return` `False` `   `  `  ``#Run a loop from 2 to n/2 ` `  ``for` `i ``in` `range``(``2``,(n``/``/``2``)``+``1``): ` `    ``#if the number is divisible by i, then n is not a prime number. ` `    ``if``(n``%``i``=``=``0``): ` `      ``return` `False` `   `  `  ``#otherwise, n is prime number. ` `  ``return` `True` ` `  ` `  ` `  `# Driver code ` `N ``=` `100``; ` `#check for every number from 1 to N ` `for` `i ``in` `range``(``1``,N``+``1``): ` `  ``#check if current number is prime ` `  ``if``(isPrime(i)): ` `    ``print``(i,end``=``" "``) `

## C#

 `// C# program to display  ` `// Prime numbers till N ` `using` `System; ` `     `  `class` `GFG  ` `{ ` `   `  ` ``//function to check if a given number is prime ` ` ``static` `bool` `isPrime(``int` `n){ ` `      ``//since 0 and 1 is not prime return false. ` `     ``if``(n==1||n==0)``return` `false``; ` `   `  `      ``//Run a loop from 2 to n/2. ` `      ``for``(``int` `i=2; i<=n/2; i++){ ` `        ``// if the number is divisible by i, then n is not a prime number. ` `        ``if``(n%i==0)``return` `false``; ` `      ``} ` `  ``//otherwise, n is prime number. ` `  ``return` `true``; ` `} ` ` `  `// Driver code  ` `public` `static` `void` `Main (String[] args)  ` `{  ` `    ``int` `N = 100;  ` `    ``//check for every number from 1 to N ` `      ``for``(``int` `i=1; i<=N; i++){ ` `      ``//check if current number is prime ` `      ``if``(isPrime(i)) { ` `        ``Console.Write(i + ``" "``);  ` `      ``} ` `    ``} ` `     `  `} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

## Javascript

 ``

Output

`2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 `

Time Complexity: O(N2),

Auxiliary Space: O(1), since no extra space has been taken.

Approach 3: If a number ‘n’ is not divided by any number less than or equals to the square root of n then, it will not be divided by any other number greater than the square root of n. So, we only need to check up to the square root of n.

## C++

 `// C++ program to display Prime numbers till N ` `#include ` `using` `namespace` `std; ` ` `  `//function to check if a given number is prime ` `bool` `isPrime(``int` `n){ ` `  ``//since 0 and 1 is not prime return false. ` `  ``if``(n==1||n==0)``return` `false``; ` `   `  `  ``//Run a loop from 2 to square root of n. ` `  ``for``(``int` `i=2; i*i<=n; i++){ ` `    ``// if the number is divisible by i, then n is not a prime number. ` `    ``if``(n%i==0)``return` `false``; ` `  ``} ` `  ``//otherwise, n is prime number. ` `  ``return` `true``; ` `} ` ` `  ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `N = 100; ` ` `  `    ``//check for every number from 1 to N ` `      ``for``(``int` `i=1; i<=N; i++){ ` `      ``//check if current number is prime ` `      ``if``(isPrime(i)) { ` `        ``cout << i << ``" "``; ` `      ``} ` `    ``} ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java program to display  ` `// Prime numbers till N ` `class` `GFG  ` `{ ` `  ``//function to check if a given number is prime ` ` ``static` `boolean` `isPrime(``int` `n){ ` `  ``//since 0 and 1 is not prime return false. ` `  ``if``(n==``1``||n==``0``)``return` `false``; ` `   `  `  ``//Run a loop from 2 to square root of n ` `  ``for``(``int` `i=``2``; i*i<=n; i++){ ` `    ``// if the number is divisible by i, then n is not a prime number. ` `    ``if``(n%i==``0``)``return` `false``; ` `  ``} ` `  ``//otherwise, n is prime number. ` `  ``return` `true``; ` `} ` `     `  ` `  `// Driver code  ` `public` `static` `void` `main (String[] args)  ` `{  ` `    ``int` `N = ``100``;  ` `        ``//check for every number from 1 to N ` `      ``for``(``int` `i=``1``; i<=N; i++){ ` `      ``//check if current number is prime ` `      ``if``(isPrime(i)) { ` `        ``System.out.print(i + ``" "``); ` `      ``} ` `    ``} ` `     `  `} ` `} `

## Python3

 `# Python3 program to display Prime numbers till N ` ` `  `#function to check if a given number is prime ` `def` `isPrime(n): ` `  ``#since 0 and 1 is not prime return false. ` `  ``if``(n``=``=``1` `or` `n``=``=``0``): ` `    ``return` `False` `   `  `  ``#Run a loop from 2 to square root of n. ` `  ``for` `i ``in` `range``(``2``,``int``(n``*``*``(``1``/``2``))``+``1``): ` `    ``#if the number is divisible by i, then n is not a prime number. ` `    ``if``(n``%``i``=``=``0``): ` `      ``return` `False` `   `  `  ``#otherwise, n is prime number. ` `  ``return` `True` ` `  ` `  ` `  `# Driver code ` `N ``=` `100``; ` `#check for every number from 1 to N ` `for` `i ``in` `range``(``1``,N``+``1``): ` `  ``#check if current number is prime ` `  ``if``(isPrime(i)): ` `    ``print``(i,end``=``" "``) `

## C#

 `// C# program to display  ` `// Prime numbers till N ` `using` `System; ` `     `  `class` `GFG  ` `{ ` `   `  ` ``//function to check if a given number is prime ` ` ``static` `bool` `isPrime(``int` `n){ ` `      ``//since 0 and 1 is not prime return false. ` `     ``if``(n==1||n==0)``return` `false``; ` `   `  `      ``//Run a loop from 2 to square root of n. ` `      ``for``(``int` `i=2; i*i<=n; i++){ ` `        ``// if the number is divisible by i, then n is not a prime number. ` `        ``if``(n%i==0)``return` `false``; ` `      ``} ` `  ``//otherwise, n is prime number. ` `  ``return` `true``; ` `} ` ` `  `// Driver code  ` `public` `static` `void` `Main (String[] args)  ` `{  ` `    ``int` `N = 100;  ` `    ``//check for every number from 1 to N ` `      ``for``(``int` `i=1; i<=N; i++){ ` `      ``//check if current number is prime ` `      ``if``(isPrime(i)) { ` `        ``Console.Write(i + ``" "``);  ` `      ``} ` `    ``} ` `     `  `} ` `} ` ` `  `// This code is contributed by Rajput-Ji `

## Javascript

 ``

Output

`2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 `

Time Complexity: O(N^(3/2)),

Auxiliary Space: O(1)

You can further optimize the time complexity to O(n*log(log(n))). Check Sieve of Eratosthenes.

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