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Program to check if input is an integer or a string

  • Difficulty Level : Easy
  • Last Updated : 04 May, 2021

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.

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

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

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 contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 

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