Check if a given string is a comment or not

Given a string S, representing a line in a program, the task is to check if the given string is a comment or not. 

Types of comments in programs:

• Single Line Comment: Comments preceded by a Double Slash ('//')
• Multi-line Comment: Comments starting with ('/*') and ending with ('*/').

Examples:  

Input: line = "/*GeeksForGeeks GeeksForGeeks*/" 
Output: It is a multi-line comment

Input: line = "// GeeksForGeeks GeeksForGeeks" 
Output: It is a single-line comment 

Approach: The idea is to check whether the input string is a comment or not. Below are the steps: 

• Check if at the first Index(i.e. index 0) the value is '/' then follow below steps else print "It is not a comment".
• If line[0] == '/':
  • If line[1] == '/', then print "It is a single line comment".
  • If line[1] == '*', then traverse the string and if any adjacent pair of '*' & '/' is found then print "It is a multi-line comment".
• Otherwise, print "It is not a comment".

Below is the implementation of the above approach: 

// C++ program for the above approach

#include <bits/stdc++.h>
using namespace std;

// Function to check if the given
// string is a comment or not
void isComment(string line)
{

    // If two continuous slashes
    // precedes the comment
    if (line.size()>=2 && line[0] == '/' && line[1] == '/') {

        cout << "It is a single-line comment";
        return;
    }

    if (line.size()>=4 && line[line.size() - 2] == '*'
        && line[line.size() - 1] == '/' && line[0] == '/' && line[1] == '*') {

        cout << "It is a multi-line comment";
        return;
    }

    cout << "It is not a comment";
}

// Driver Code
int main()
{
    // Given string
    string line = "/*GeeksForGeeks GeeksForGeeks*/";

    // Function call to check whether then
    // given string is a comment or not
    isComment(line);

    return 0;
}

// Java program for the above approach
import java.io.*;
import java.lang.*;
import java.util.*;

class GFG{

// Function to check if the given
// string is a comment or not
static void isComment(String S)
{
    char line[] = S.toCharArray();

    // If two continuous slashes
    // precedes the comment
    if (line[0] == '/' && line[1] == '/' )
    {
        System.out.println(
            "It is a single-line comment");
        return;
    }

    if (line[0]=='/' && line[1]=='*' && line[line.length - 2] == '*' && 
        line[line.length - 1] == '/')
    {
        System.out.println(
            "It is a multi-line comment");
        return;
    }

    System.out.println("It is not a comment");
}

// Driver Code
public static void main(String[] args)
{
    
    // Given string
    String line = "/*GeeksForGeeks GeeksForGeeks*/";

    // Function call to check whether then
    // given string is a comment or not
    isComment(line);
}
}

// This code is contributed by Kingash

# Python3 program for the above approach

# Function to check if the given
# string is a comment or not
def isComment(line):
  
    # If two continuous slashes
    # precedes the comment
    if (line[0] == '/'  and line[1] == '/' and line[2] != '/'):
        print("It is a single-line comment")
        return

    if (line[len(line) - 2] == '*' and line[len(line) - 1] == '/' and line[0] == '/'  and line[1] == '*'):
        print("It is a multi-line comment")
        return

    print("It is not a comment")

# Driver Code
if __name__ == '__main__':
  
    # Given string
    line = "/*GeeksForGeeks GeeksForGeeks*/"
    
    # Function call to check whether then
    # given string is a comment or not
    isComment(line)
    
    # This code is contributed by ipg2016107.

// C# program for the above approach
using System;
using System.Collections.Generic;

class GFG{
    
// Function to check if the given
// string is a comment or not
static void isComment(string S)
{
    char[] line = S.ToCharArray();

    // If two continuous slashes
    // precedes the comment
    if (line[0] == '/' && line[1] == '/' && 
        line[2] != '/')
    {
        Console.WriteLine("It is a single-line comment");
        return;
    }

    if (line[line.Length - 2] == '*' && 
        line[line.Length - 1] == '/' && line[0] == '/' && line[1] == '*')
    {
        Console.WriteLine("It is a multi-line comment");
        return;
    }

    Console.WriteLine("It is not a comment");
}

// Driver Code
static public void Main()
{
    
    // Given string
    string line = "/*GeeksForGeeks GeeksForGeeks*/";

    // Function call to check whether then
    // given string is a comment or not
    isComment(line);
}
}

// This code is contributed by splevel62

<script>

// JavaScript program for the above approach
 

// Function to check if the given
// string is a comment or not
function isComment( line)
{


    // If two continuous slashes
    // precedes the comment
    var regex = new RegExp("//.*", );
    var rex = regex.test(line);
    if(rex){
        document.write("It is a single-line comment");
        return;
    }
    var regexMul = new RegExp("/\*.*?\*/", );
    var rexmul = regexMul.test(line);
    if (rexmul)
    {
        document.write("It is a multi-line comment");
        return;
    }

    document.write("It is not a comment");
}
// Driver Code

// Given string
var line = "/*GeeksForGeeks GeeksForGeeks*/";

// Function call to check whether then
// given string is a comment or not
isComment(line);

    
    
</script>

It is a multi-line comment

Time Complexity: O(N)
Auxiliary Space: O(1)