Program to check if input is an integer or a string

• Difficulty Level : Easy
• Last Updated : 15 Jun, 2022

Write a function to check whether a given input is an integer or a string.

Definition of an integer :

`Every element should be a valid digit, i.e '0-9'.`

Definition of a string :

`Any one element should be an invalid digit, i.e any symbol other than '0-9'.`

Examples:

```Input : 127
Output : Integer
Explanation : All digits are in the range '0-9'.

Input : 199.7
Output : String
Explanation : A dot is present.

Input : 122B
Output : String
Explanation : A alphabet is present.```

Method 1: The idea is to use isdigit() function and is_numeric() function..

Below is the implementation of the above idea.

C++

 `// CPP program to check if a given string` `// is a valid integer` `#include ` `using` `namespace` `std;`   `// Returns true if s is a number else false` `bool` `isNumber(string s)` `{` `    ``for` `(``int` `i = 0; i < s.length(); i++)` `        ``if` `(``isdigit``(s[i]) == ``false``)` `            ``return` `false``;`   `    ``return` `true``;` `}`   `// Driver code` `int` `main()` `{` `    ``// Saving the input in a string` `    ``string str = ``"6790"``;`   `    ``// Function returns 1 if all elements` `    ``// are in range '0-9'` `    ``if` `(isNumber(str))` `        ``cout << ``"Integer"``;`   `    ``// Function returns 0 if the input is` `    ``// not an integer` `    ``else` `        ``cout << ``"String"``;` `}`

Java

 `// Java program to check if a given` `// string is a valid integer` `import` `java.io.*;`   `public` `class` `GFG {`   `    ``// Returns true if s is` `    ``// a number else false` `    ``static` `boolean` `isNumber(String s)` `    ``{` `        ``for` `(``int` `i = ``0``; i < s.length(); i++)` `            ``if` `(Character.isDigit(s.charAt(i)) == ``false``)` `                ``return` `false``;`   `        ``return` `true``;` `    ``}`   `    ``// Driver code` `    ``static` `public` `void` `main(String[] args)` `    ``{` `        ``// Saving the input in a string` `        ``String str = ``"6790"``;`   `        ``// Function returns 1 if all elements` `        ``// are in range '0 - 9'` `        ``if` `(isNumber(str))` `            ``System.out.println(``"Integer"``);`   `        ``// Function returns 0 if the` `        ``// input is not an integer` `        ``else` `            ``System.out.println(``"String"``);` `    ``}` `}`   `// This code is contributed by vt_m.`

Python 3

 `# Python 3 program to check if a given string` `# is a valid integer`   `# This function Returns true if` `# s is a number else false` `def` `isNumber(s):`   `    ``for` `i ``in` `range``(``len``(s)):` `        ``if` `s[i].isdigit() !``=` `True``:` `            ``return` `False`   `    ``return` `True`     `# Driver code` `if` `__name__ ``=``=` `"__main__"``:`   `    ``# Store the input in a str variable` `    ``str` `=` `"6790"`   `    ``# Function Call` `    ``if` `isNumber(``str``):` `        ``print``(``"Integer"``)`   `    ``else``:` `        ``print``(``"String"``)`   `# This code is contributed by ANKITRAI1`

C#

 `// C# program to check if a given` `// string is a valid integer` `using` `System;`   `public` `class` `GFG {`   `    ``// Returns true if s is a` `    ``// number else false` `    ``static` `bool` `isNumber(``string` `s)` `    ``{` `        ``for` `(``int` `i = 0; i < s.Length; i++)` `            ``if` `(``char``.IsDigit(s[i]) == ``false``)` `                ``return` `false``;`   `        ``return` `true``;` `    ``}`   `    ``// Driver code` `    ``static` `public` `void` `Main(String[] args)` `    ``{`   `        ``// Saving the input in a string` `        ``string` `str = ``"6790"``;`   `        ``// Function returns 1 if all elements` `        ``// are in range '0 - 9'` `        ``if` `(isNumber(str))` `            ``Console.WriteLine(``"Integer"``);`   `        ``// Function returns 0 if the` `        ``// input is not an integer` `        ``else` `            ``Console.WriteLine(``"String"``);` `    ``}` `}`   `// This code is contributed by vt_m.`

PHP

 ``

Javascript

 ``

Output

`Integer`

Time Complexity: O(n)

Auxiliary Space: O(1)

Method 2: Using special Python built-in type() function:

type() is a built-in function provided by python . type() takes object as parameter and returns its class type as its name says.

Below is the implementation of the above idea:

Python3

 `# Python program to find` `# whether the user input` `# is int or string type`   `# Function to determine whether ` `# the user input is string or` `# integer type` `def` `isNumber(x):` `    ``if` `type``(x) ``=``=` `int``:` `         ``return` `True` `    ``else``:` `         ``return` `False`     `# Driver Code` `input1 ``=` `122` `input2 ``=` `'122'`   `# Function Call`   `# for input1` `if` `isNumber(input1):` `    ``print``(``"Integer"``)` `else``:` `    ``print``(``"String"``)`   `# for input2` `if` `isNumber(input2):` `    ``print``(``"Integer"``)` `else``:` `    ``print``(``"String"``)`

Output

```Integer
String```

Time Complexity: O(1)

Auxiliary Space: O(1)

Method 3: Using Integer.parseInt() in Java

The parseInt() method of Integer class is used to parse a given string into an integer provided that the string contains a valid integer. In case, the string doesn’t contain a valid integer, it throws a NumberFormatException. The idea is to parse the given string using the same. If an exception is found, then the given string will not be a valid integer and vice-versa.

Below is the implementation of the above idea:

Java

 `// Java program to check if a given` `// string is a valid integer` `import` `java.io.*;`   `public` `class` `GFG {`   `    ``// Driver code` `    ``static` `public` `void` `main(String[] args)` `    ``{` `        ``String s = ``"abc"``; ``//sample input to test` `        ``try``{` `            ``Integer.parseInt(s);` `            ``System.out.println(``"Integer"``);` `        ``}``catch``(NumberFormatException e){` `            ``System.out.println(``"String"``);` `        ``} ` `    ``}` `}`   `// This code is contributed by shruti456rawal`

Output

`String`

Time Complexity: O(N) where N is length of string.

Auxiliary Space: O(1)

This article is contributed by Rohit Thapliyal. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to review-team@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.