# How to check string is alphanumeric or not using Regular Expression

Last Updated : 03 Jan, 2023

Given string str, the task is to check whether the string is alphanumeric or not by using Regular Expression

An alphanumeric string is a string that contains only alphabets from a-z, A-Z and some numbers from 0-9.

Examples:

Input: str = “GeeksforGeeks123”
Output: true
Explanation:
This string contains all the alphabets from a-z, A-Z, and the number from 0-9. Therefore, it is an alphanumeric string.
Input: str = “GeeksforGeeks”
Output: false
Explanation:
This string contains all the alphabets from a-z, A-Z, but doesn’t contain any number from 0-9. Therefore, it is not an alphanumeric string.
Input: str = “GeeksforGeeks123@#”
Output: false
Explanation:
This string contains all the alphabets from a-z, A-Z, and the number from 0-9 along with some special symbols. Therefore, it is not an alphanumeric string.

Approach: This problem can be solved by using Regular Expression.

• Get the string.
• Create a regular expression to check string is alphanumeric or not as mentioned below:
`regex = "^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$";`
• Where:
• ^ represents the starting of the string
• (?=.*[a-zA-Z]) represents the alphabets from a-z, A-Z
• (?=.*[0-9]) represents any number from 0-9
• [A-Za-z0-9] represents whether everything is either alphabetical or digit
• + represents one or more times
• \$ represents the ending of the string
• Match the given string with the regex, in Java, this can be done by using Pattern.matcher()
• Return true if the string matches with the given regex, else return false

Below is the implementation of the above approach.

## C++

 `// C++ program to check`   `// String is alphanumeric or not using Regular Expression` `#include ` `#include `   `using` `namespace` `std;`   `// Function to validate the // String is alphanumeric or not using Regular Expression` `bool` `isAlphaNumeric(string str) {`   `// Regex to check valid  alphanumeric String. ` `  ``const` `regex pattern(``"^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$"``);`   `// If the string`   `// is empty return false` `  ``if` `(str.empty())` `  ``{ ` `    ``return` `false``;` `  ``}`     `// Return true if the String`   `// matched the ReGex`   `if` `(regex_match(str, pattern))` `{ ` `return` `true``;;` `}` `else` `{` `  ``return` `false``;` `}` `}`   `// Driver Code`   `int` `main()`   `{` `  ``// Test Case 1:` `string str1= ``"GeeksforGeeks123"``; ` `cout <

## Java

 `// Java program to check string is` `// alphanumeric or not using Regular Expression.`   `import` `java.util.regex.*;`   `class` `GFG {`   `    ``// Function to check string is alphanumeric or not` `    ``public` `static` `boolean` `isAlphaNumeric(String str)` `    ``{` `        ``// Regex to check string is alphanumeric or not.` `        ``String regex = ``"^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$"``;`   `        ``// Compile the ReGex` `        ``Pattern p = Pattern.compile(regex);`   `        ``// If the string is empty` `        ``// return false` `        ``if` `(str == ``null``) {` `            ``return` `false``;` `        ``}`   `        ``// Pattern class contains matcher() method` `        ``// to find matching between given string` `        ``// and regular expression.` `        ``Matcher m = p.matcher(str);`   `        ``// Return if the string` `        ``// matched the ReGex` `        ``return` `m.matches();` `    ``}`   `    ``// Driver Code.` `    ``public` `static` `void` `main(String args[])` `    ``{`   `        ``// Test Case 1:` `        ``String str1 = ``"GeeksforGeeks123"``;` `        ``System.out.println(` `            ``str1 + ``": "` `            ``+ isAlphaNumeric(str1));`   `        ``// Test Case 2:` `        ``String str2 = ``"GeeksforGeeks"``;` `        ``System.out.println(` `            ``str2 + ``": "` `            ``+ isAlphaNumeric(str2));`   `        ``// Test Case 3:` `        ``String str3 = ``"GeeksforGeeks123@#"``;` `        ``System.out.println(` `            ``str3 + ``": "` `            ``+ isAlphaNumeric(str3));`   `        ``// Test Case 4:` `        ``String str4 = ``"123"``;` `        ``System.out.println(` `            ``str4 + ``": "` `            ``+ isAlphaNumeric(str4));`   `        ``// Test Case 5:` `        ``String str5 = ``"@#"``;` `        ``System.out.println(` `            ``str5 + ``": "` `            ``+ isAlphaNumeric(str5));` `    ``}` `}`

## Python3

 `# Python3 program to check ` `# string is alphanumeric or` `# not using Regular Expression. ` `import` `re`   `# Function to check string ` `# is alphanumeric or not` `def` `isAlphaNumeric(``str``):`   `    ``# Regex to check string is ` `    ``# alphanumeric or not.` `    ``regex ``=` `"^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$"`   `    ``# Compile the ReGex` `    ``p ``=` `re.``compile``(regex)`   `    ``# If the string is empty ` `    ``# return false` `    ``if``(``str` `=``=` `None``):` `        ``return` `False`   `    ``# Return if the string ` `    ``# matched the ReGex ` `    ``if``(re.search(p, ``str``)):` `        ``return` `True` `    ``else``:` `        ``return` `False`   `# Driver Code`   `# Test Case 1:` `str1 ``=` `"GeeksforGeeks123"` `print``(str1, ``":"``, ` `      ``isAlphaNumeric(str1))`   `# Test Case 2:` `str2 ``=` `"GeeksforGeeks"` `print``(str2, ``":"``, ` `      ``isAlphaNumeric(str2))`   `# Test Case 3:` `str3 ``=` `"GeeksforGeeks123@#"` `print``(str3, ``":"``, ` `      ``isAlphaNumeric(str3))`   `# Test Case 4:` `str4 ``=` `"123"` `print``(str4, ``":"``, ` `      ``isAlphaNumeric(str4))`   `# Test Case 5:` `str5 ``=` `"@#"` `print``(str5, ``":"``, ` `      ``isAlphaNumeric(str5))`   `# This code is contributed by avanitrachhadiya2155`

## C#

 `// C# program to check` `// String is alphanumeric or not using Regular Expression` `using` `System;` `using` `System.Text.RegularExpressions;` `class` `GFG` `{`   `  ``// Main Method` `  ``static` `void` `Main(``string``[] args)` `  ``{`   `    ``// Input strings to Match` `    ``// String is alphanumeric or not` `    ``string``[] str={``"GeeksforGeeks123"``,``"GeeksforGeeks"` `,` `                  ``"GeeksforGeeks123@#"``,``"123"``,` `                  ``"@#"``};` `    ``foreach``(``string` `s ``in` `str) {` `      ``Console.WriteLine( isAlphaNumeric(s) ? ``"true"` `: ``"false"``);` `    ``}` `    ``Console.ReadKey(); }`   `  ``// method containing the regex` `  ``public` `static` `bool` `isAlphaNumeric(``string` `str)` `  ``{` `    ``string` `strRegex = ``@"^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$"``;` `    ``Regex re = ``new` `Regex(strRegex);` `    ``if` `(re.IsMatch(str))` `      ``return` `(``true``);` `    ``else` `      ``return` `(``false``);` `  ``}` `}`   `// This code is contributed by Rahul Chauhan`

## Javascript

 `// Javascript program to check` `// String is alphanumeric or not using Regular Expression`   `// Function to validate the` `// string ` `function` `isAlphaNumeric(str) {` `    ``// Regex to check valid` `    ``// alphanumeric string  ` `    ``let regex = ``new` `RegExp(/^(?=.*[a-zA-Z])(?=.*[0-9])[A-Za-z0-9]+\$/);`   `    ``// if str ` `    ``// is empty return false` `    ``if` `(str == ``null``) {` `        ``return` `"false"``;` `    ``}`   `    ``// Return true if the str` `    ``// matched the ReGex` `    ``if` `(regex.test(str) == ``true``) {` `        ``return` `"true"``;` `    ``}` `    ``else` `{` `        ``return` `"false"``;` `    ``}` `}`   `// Driver Code` `// Test Case 1:` `let str1 = ``"GeeksforGeeks123"``;` `console.log(isAlphaNumeric(str1));`   `// Test Case 2:` `let str2 = ``"GeeksforGeeks"``;` `console.log(isAlphaNumeric(str2));`   `// Test Case 3:` `let str3 = ``"GeeksforGeeks123@#"``;` `console.log(isAlphaNumeric(str3));`   `// Test Case 4:` `let str4 = ``"#123"``;` `console.log(isAlphaNumeric(str4));`   `// Test Case 5:` `let str5 = ``"#@#"``;` `console.log(isAlphaNumeric(str5));`   `// This code is contributed by Rahul Chauhan`

Output:

```GeeksforGeeks123: true
GeeksforGeeks: false
GeeksforGeeks123@#: false
123: false
@#: false```