Program to check if input is an integer or a string

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 the length of the string.
Auxiliary Space: O(1)

Method 4: Traverse and check if ASCII range falls under (0-9)

This method/algo is that traverse through the string and checks if ASCII range of every character falls under (0-9) or not. If every character is in range (48-57) then it prints that the string is an integer otherwise it is a string.

C++

// CPP program to check if a given string
// is a valid integer
#include <iostream>
using namespace std;

// Function to check if st is number or not
bool isNumber(string st){
      int i = 0;
    while (st[i] != NULL) {
        if (st[i] < 48 || st[i] > 57)
            return false;
        i++;
    }
    return true;
}

int main(){

    // Saving the input in a string
    string st = "122B";

    // Function returns true if all elements are in
    // range '0-9'
    if (isNumber(st))
        cout << "Integer";

    // Function returns false if the input is not an
    // integer, a string
    else
        cout << "String";

    return 0;
}

// This code is contributed by Susobhan Akhuli

Java

import java.io.*;

public class GFG {
    // Returns true if st is a number else false
    static boolean isNumber(String st) {
        for (int i = 0; i < st.length(); i++)
            if (st.charAt(i) < 48 || st.charAt(i) > 57)
                return false;
        return true;
    }

    public static void main(String[] args) {

        // Saving the input in a string
        String st = "122B";

        // Function returns true if all elements are in
        // range '0-9'
        if (isNumber(st))
            System.out.println("Integer");

        // Function returns false if the input is not an
        // integer, a string
        else
            System.out.println("String");
    }
}

// This code is contributed by Susobhan Akhuli

C#

using System;

public class Program {
    // Returns true if st is a number else false
    static bool isNumber(string st)
    {
        for (int i = 0; i < st.Length; i++)
            if (st[i] < 48 || st[i] > 57)
                return false;
        return true;
    }

    static void Main(string[] args)
    {
        // Saving the input in a string
        string st = "122B";

        // Function returns true if all elements are in
        // range '0-9'
        if (isNumber(st))
            Console.WriteLine("Integer");

        // Function returns false if the input is not an
        // integer, a string
        else
            Console.WriteLine("String");
    }
}

Javascript

// Javascript program to check if a given string
// is a valid integer

// Function to check if st is number or not
function isNumber(st){
    let i = 0;
    while (st[i] != null) {
        if (st[i] < 48 || st[i] > 57)
            return false;
        i++;
    }
    return true;
}

    // Saving the input in a string
let st = "122B";

// Function returns true if all elements are in
// range '0-9'
if (isNumber(st))
    console.log("Integer");

// Function returns false if the input is not an
// integer, a string
else
    console.log("String");

Output

String

Time Complexity: O(N) where N is the length of the string.
Auxiliary Space: O(1)

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