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Program to check if input is an integer or a string

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  • Difficulty Level : Easy
  • Last Updated : 14 Jul, 2022
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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 <iostream>
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




<?php
// PHP program to check if a
// given string is a valid integer
 
// Returns true if s
// is a number else false
function isNumber($s)
{
    for ($i = 0; $i < strlen($s); $i++)
        if (is_numeric($s[$i]) == false)
            return false;
 
    return true;
}
 
// Driver code
 
// Saving the input
// in a string
$str = "6790";
 
// Function returns
// 1 if all elements
// are in range '0-9'
if (isNumber($str))
    echo "Integer";
else
    echo "String";
 
// This code is contributed by ajit
?>


Javascript




<script>
    // Javascript program to check if a given
    // string is a valid integer
     
    // Returns true if s is a
    // number else false
    function isNumber(s)
    {
        for (let i = 0; i < s.length; i++)
            if (s[i] < '0' || s[i] > '9')
                return false;
  
        return true;
    }
     
    // Saving the input in a string
    let str = "6790";
 
    // Function returns 1 if all elements
    // are in range '0 - 9'
    if (isNumber(str))
      document.write("Integer");
 
    // Function returns 0 if the
    // input is not an integer
    else
      document.write("String");
     
</script>


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. 


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