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Program to find Prime Numbers Between given Interval
• Difficulty Level : Easy
• Last Updated : 06 Nov, 2020 Given two numbers  a and b as interval range, the task is to find the prime numbers in between this interval.

Examples:

```Input : a = 1, b = 10
Output : 2, 3, 5, 7

Input : a = 10, b = 20
Output : 11, 13, 17, 19
```

In the below program, the range of numbers is taken as input and stored in the variables ‘a’ and ‘b’. Then using for-loop, the numbers between the interval of a and b are traversed. For each number in the for loop, it is checked if this number is prime or not. If found prime, print the number. Then the next number in the loop is checked, till all numbers are checked.

Program:

## C++

 `// C++ program to find the prime numbers` `// between a given interval`   `#include ` `using` `namespace` `std;`   `int` `main()` `{` `    ``// Declare the variables` `    ``int` `a, b, i, j, flag;`   `    ``// Ask user to enter lower value of interval` `    ``cout << ``"Enter lower bound of the interval: "``;` `    ``cin >> a; ``// Take input`   `    ``// Ask user to enter upper value of interval` `    ``cout << ``"\nEnter upper bound of the interval: "``;` `    ``cin >> b; ``// Take input`   `    ``// Print display message` `    ``cout << ``"\nPrime numbers between "` `         ``<< a << ``" and "` `<< b << ``" are: "``;`   `    ``// Traverse each number in the interval` `    ``// with the help of for loop` `    ``for` `(i = a; i <= b; i++) {` `        ``// Skip 0 and 1 as they are` `        ``// niether prime nor composite` `        ``if` `(i == 1 || i == 0)` `            ``continue``;`   `        ``// flag variable to tell` `        ``// if i is prime or not` `        ``flag = 1;`   `        ``for` `(j = 2; j <= i / 2; ++j) {` `            ``if` `(i % j == 0) {` `                ``flag = 0;` `                ``break``;` `            ``}` `        ``}`   `        ``// flag = 1 means i is prime` `        ``// and flag = 0 means i is not prime` `        ``if` `(flag == 1)` `            ``cout << i << ``" "``;` `    ``}`   `    ``return` `0;` `}`   `// This code is contributed by Akanksha Rai`

## C

 `// C program to find the prime numbers` `// between a given interval`   `#include `   `int` `main()` `{` `    ``// Declare the variables` `    ``int` `a, b, i, j, flag;`   `    ``// Ask user to enter lower value of interval` `    ``printf``(``"Enter lower bound of the interval: "``);` `    ``scanf``(``"%d"``, &a); ``// Take input`   `    ``// Ask user to enter upper value of interval` `    ``printf``(``"\nEnter upper bound of the interval: "``);` `    ``scanf``(``"%d"``, &b); ``// Take input`   `    ``// Print display message` `    ``printf``(``"\nPrime numbers between %d and %d are: "``, a, b);`   `    ``// Traverse each number in the interval` `    ``// with the help of for loop` `    ``for` `(i = a; i <= b; i++) {` `        ``// Skip 0 and 1 as they are` `        ``// niether prime nor composite` `        ``if` `(i == 1 || i == 0)` `            ``continue``;`   `        ``// flag variable to tell` `        ``// if i is prime or not` `        ``flag = 1;`   `        ``for` `(j = 2; j <= i / 2; ++j) {` `            ``if` `(i % j == 0) {` `                ``flag = 0;` `                ``break``;` `            ``}` `        ``}`   `        ``// flag = 1 means i is prime` `        ``// and flag = 0 means i is not prime` `        ``if` `(flag == 1)` `            ``printf``(``"%d "``, i);` `    ``}`   `    ``return` `0;` `}`

## Java

 `import` `java.util.Scanner;`   `// Java program to find the prime numbers` `// between a given interval` `public` `class` `GFG {`   `    ``// driver code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``Scanner sc = ``new` `Scanner(System.in);` `        ``// Declare the variables` `        ``int` `a, b, i, j, flag;`   `        ``// Ask user to enter lower value of interval` `        ``System.out.printf(``"Enter lower bound of the interval: "``);` `        ``a = sc.nextInt(); ``// Take input`   `        ``// Ask user to enter upper value of interval` `        ``System.out.printf(``"\nEnter upper bound of the interval: "``);` `        ``b = sc.nextInt(); ``// Take input`   `        ``// Print display message` `        ``System.out.printf(``"\nPrime numbers between %d and %d are: "``, a, b);`   `        ``// Traverse each number in the interval` `        ``// with the help of for loop` `        ``for` `(i = a; i <= b; i++) {`   `            ``// Skip 0 and 1 as they are` `            ``// niether prime nor composite` `            ``if` `(i == ``1` `|| i == ``0``)` `                ``continue``;`   `            ``// flag variable to tell` `            ``// if i is prime or not` `            ``flag = ``1``;`   `            ``for` `(j = ``2``; j <= i / ``2``; ++j) {` `                ``if` `(i % j == ``0``) {` `                    ``flag = ``0``;` `                    ``break``;` `                ``}` `            ``}`   `            ``// flag = 1 means i is prime` `            ``// and flag = 0 means i is not prime` `            ``if` `(flag == ``1``)` `                ``System.out.println(i);` `        ``}` `    ``}` `}`

## Python3

 `# Python3 program to find the prime ` `# numbers between a given interval`   `if` `__name__ ``=``=` `'__main__'``:` `    `  `    ``# Declare the variables` `    ``a, b, i, j, flag ``=` `0``, ``0``, ``0``, ``0``, ``0`   `    ``# Ask user to enter lower value of interval` `    ``print``(``"Enter lower bound of the interval:"``, ` `                                      ``end ``=` `"")` `    ``a ``=` `int``(``input``()) ``# Take input` `    ``print``(a)` `    `  `    ``# Ask user to enter upper value of interval` `    ``print``(``"Enter upper bound of the interval:"``, ` `                                      ``end ``=` `"")` `    ``b ``=` `int``(``input``()) ``# Take input` `    ``print``(b)` `    `  `    ``# Print display message` `    ``print``(``"Prime numbers between"``, a, ``"and"``, ` `                        ``b, ``"are:"``, end ``=` `"")`   `    ``# Traverse each number in the interval` `    ``# with the help of for loop` `    ``for` `i ``in` `range``(a, b ``+` `1``):`   `        ``# Skip 1 as1 is niether` `        ``# prime nor composite` `        ``if` `(i ``=``=` `1``):` `            ``continue`   `        ``# flag variable to tell` `        ``# if i is prime or not` `        ``flag ``=` `1` `        `  `        ``for` `j ``in` `range``(``2``, i ``/``/` `2` `+` `1``):` `            ``if` `(i ``%` `j ``=``=` `0``):` `                ``flag ``=` `0` `                ``break` `            `  `        ``# flag = 1 means i is prime` `        ``# and flag = 0 means i is not prime` `        ``if` `(flag ``=``=` `1``):` `            ``print``(i, end ``=` `" "``)` `            `  `# This code is contributed ` `# by Mohit kumar 29`

## C#

 `// C# program to find the prime numbers` `// between a given interval` `using` `System;`   `class` `GFG{`   `// Driver code    ` `public` `static` `void` `Main(``string``[] args) ` `{ ` `    `  `    ``// Declare the variables` `    ``int` `a, b, i, j, flag;`   `    ``// Ask user to enter lower value of interval` `    ``Console.WriteLine(``"Enter lower bound of "` `+` `                      ``"the interval: "``);` `                      `  `    ``// Take input` `    ``a = ``int``.Parse(Console.ReadLine()); `   `    ``// Ask user to enter upper value of interval` `    ``Console.WriteLine(``"\nEnter upper bound "` `+ ` `                      ``"of the interval: "``);` `                      `  `    ``// Take input` `    ``b = ``int``.Parse(Console.ReadLine()); `   `    ``// Print display message` `    ``Console.WriteLine(``"\nPrime numbers between "` `+  ` `                      ``"{0} and {1} are: "``, a, b);`   `    ``// Traverse each number in the interval` `    ``// with the help of for loop` `    ``for``(i = a; i <= b; i++)` `    ``{` `        `  `        ``// Skip 0 and 1 as they are` `        ``// niether prime nor composite` `        ``if` `(i == 1 || i == 0)` `            ``continue``;`   `        ``// flag variable to tell` `        ``// if i is prime or not` `        ``flag = 1;`   `        ``for``(j = 2; j <= i / 2; ++j)` `        ``{` `            ``if` `(i % j == 0) ` `            ``{` `                ``flag = 0;` `                ``break``;` `            ``}` `        ``}`   `        ``// flag = 1 means i is prime` `        ``// and flag = 0 means i is not prime` `        ``if` `(flag == 1)` `            ``Console.WriteLine(i);` `    ``}` `}` `}`   `// This code is contributed by jana_sayantan`

Output:

```Enter lower bound of the interval: 1
Enter upper bound of the interval: 10
Prime numbers between 1 and 10 are: 2 3 5 7
```

Optimized Solution :
The idea is to use the fact that even numbers (except 2) are not primes.

## C++

 `// C++ program to find the prime numbers` `// between a given interval`   `#include ` `using` `namespace` `std;`   `int` `main()` `{` `    ``// Declare the variables` `    ``int` `a, b, i, j;`   `    ``// Ask user to enter lower value of interval please not` `    ``// interval < 0 cannot be prime numbers` `    ``cout << ``"Enter lower bound of the interval: "``;` `    ``cin >> a; ``// Take input`   `    ``// Ask user to enter upper value of interval` `    ``cout << ``"\nEnter upper bound of the interval: "``;` `    ``cin >> b; ``// Take input`   `    ``// Print display message` `    ``cout << ``"\nPrime numbers between "` `<< a << ``" and "` `<< b` `         ``<< ``" are: "``;`   `    ``// Explicitly handling the cases when a is less than 2` `    ``// since 0 and 1 are not prime numbers` `    ``if` `(a <= 2) {` `        ``a = 2;` `        ``if` `(b >= 2) {` `            ``cout << a << ``" "``;` `            ``a++;` `        ``}` `    ``}`   `    ``// MAKING SURE THAT a IS ODD BEFORE WE BEGIN` `    ``// THE LOOP` `    ``if` `(a % 2 == 0)` `        ``a++;`   `    ``// NOTE : WE TRAVERSE THROUGH ODD NUMBERS ONLY` `    ``for` `(i = a; i <= b; i = i + 2) {`   `        ``// flag variable to tell` `        ``// if i is prime or not` `        ``bool` `flag = 1;`   `        ``// WE TRAVERSE TILL SQUARE ROOT OF j only.` `        ``// (LARGEST POSSIBLE VALUE OF A PRIME FACTOR)` `        ``for` `(j = 2; j * j <= i; ++j) {` `            ``if` `(i % j == 0) {` `                ``flag = 0;` `                ``break``;` `            ``}` `        ``}`   `        ``// flag = 1 means i is prime` `        ``// and flag = 0 means i is not prime` `        ``if` `(flag == 1)` `            ``cout << i << ``" "``;` `    ``}`   `    ``return` `0;` `}`

## Java

 `// Java program to find the prime numbers` `// between a given interval` `import` `java.util.Scanner;` ` `  `class` `GFG {` ` `  `    ``// driver code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``Scanner sc = ``new` `Scanner(System.in);` `         ``// Declare the variables` `    ``int` `a, b, i, j,flag;`   `    ``// Ask user to enter lower value of interval` `    ``System.out.printf( ``"Enter lower bound of the interval: "``);` `    ``a = sc.nextInt(); ``// Take input`   `    ``// Ask user to enter upper value of interval` `    ``System.out.printf( ``"\nEnter upper bound of the interval: "``);` `    ``b = sc.nextInt(); ``// Take input`   `    ``// Print display message` `    ``System.out.printf(``"\nPrime numbers between %d and %d are: "``, a, b);`   `    ``// Explicitly handling the cases when a is less than 2` `    ``if` `(a == ``1``) {` `        ``System.out.println(a);` `        ``a++;` `        ``if` `(b >= ``2``) {` `            ``System.out.println(a);` `            ``a++;` `        ``}` `    ``}` `    ``if` `(a == ``2``)` `        ``System.out.println(a);`   `    ``// MAKING SURE THAT a IS ODD BEFORE WE BEGIN ` `    ``// THE LOOP` `    ``if` `(a % ``2` `== ``0``)` `        ``a++;`   `    ``// NOTE : WE TRAVERSE THROUGH ODD NUMBERS ONLY` `    ``for` `(i = a; i <= b; i = i + ``2``) {`   `        ``// flag variable to tell` `        ``// if i is prime or not` `         ``flag = ``1``;`   `        ``// WE TRAVERSE TILL SQUARE ROOT OF j only.` `        ``// (LARGEST POSSIBLE VALUE OF A PRIME FACTOR)` `        ``for` `(j = ``2``; j * j <= i; ++j) {` `            ``if` `(i % j == ``0``) {` `                ``flag = ``0``;` `                ``break``;` `            ``}` `        ``}`   `        ``// flag = 1 means i is prime` `        ``// and flag = 0 means i is not prime` `        ``if` `(flag == ``1``)` `            ``System.out.println(i);` `    ``}`   `    ``}` `}`   `// This code is contributed by shivanisinghss2110`

## Python3

 `# Python3 program to find the prime ` `# numbers between a given interval` ` `  `if` `__name__ ``=``=` `'__main__'``:` `    `  `    ``# Declare the variables` `    ``a, b, i, j ``=` `0``, ``0``, ``0``, ``0` `    `  `    ``# Ask user to enter lower value of interval` `    ``print``(``"Enter lower bound of the interval:"``,end ``=` `"")` `    `  `    ``a ``=` `int``(``input``()) ``# Take input` `    ``print``(a)` `    `  `    ``# Ask user to enter upper value of interval` `    ``print``(``"Enter upper bound of the interval:"``,end ``=` `"")` `    `  `    ``b ``=` `int``(``input``()) ``# Take input` `    ``print``(b)` `    `  `    ``# Print display message` `    ``print``(``"Prime numbers between"``, a, ``"and"``,b, ``"are:"``, end ``=` `"")` `    `  `    `  `    ``# Explicitly handling the cases when a is less than 2` `    ``if` `(a ``=``=` `1``):` `        ``print``(a,end``=``" "``)` `        ``a``+``=``1` `        ``if` `(b >``=` `2``):` `            ``print``(a,end``=``" "``)` `            ``a``+``=``1` `    ``if` `(a ``=``=` `2``):` `        ``print``(a,end``=``" "``)` `    `  `    ``# MAKING SURE THAT a IS ODD BEFORE WE BEGIN ` `    ``# THE LOOP` `    ``if` `(a ``%` `2` `=``=` `0``):` `        ``a``+``=``1` `    ``# NOTE : WE TRAVERSE THROUGH ODD NUMBERS ONLY` `    ``for` `i ``in` `range``(a,b``+``1``,``2``):` `        `  `        ``# flag variable to tell` `        ``# if i is prime or not` `        ``flag ``=` `1` `        ``# WE TRAVERSE TILL SQUARE ROOT OF j only.` `        ``# (LARGEST POSSIBLE VALUE OF A PRIME FACTOR)` `        ``j ``=` `2` `        ``while``(j ``*` `j <``=` `i):` `            ``if` `(i ``%` `j ``=``=` `0``):` `                ``flag ``=` `0` `                ``break` `            ``j``+``=``1` `        `  `        ``# flag = 1 means i is prime` `        ``# and flag = 0 means i is not prime` `        ``if` `(flag ``=``=` `1``):` `            ``print``(i,end``=``" "``)`   `# This code is contributed by shubhamsingh10`

Output:

```Enter lower bound of the interval: 1
Enter upper bound of the interval: 10
Prime numbers between 1 and 10 are: 1 2 3 5 7
```

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