字符串未被识别为有效的日期时间。 将字符串转换为日期时间

Question

I need to convert a string to a DateTime format in the following code. But I am encountering the following error. How can I solve this?

Unhandled Exception:

System.FormatException: String was not recognized as a valid DateTime.

public static int calculateAge(string dateOfBirth)
{
    // Implement code here
    int age = 0;  
    DateTime s = DateTime.ParseExact(dateOfBirth, "D", null);
    age = Convert.ToInt32(DateTime.Now.Year - s.Year);  
    if (DateTime.Now.DayOfYear < s.DayOfYear)  
        age = age - 1;  

    return age; 
}

Answer 1

This is a good time to learn to read documentation. We're dealing with the DateTime.ParseExact() method. This method has several overloads, but the documentation for the one we care about is here:

https://docs.microsoft.com/en-us/dotnet/api/system.datetime.parseexact?view=netcore-3.1#System_DateTime_ParseExact_System_String_System_String_System_IFormatProvider_

I found that link by searching Google for C# DateTime.ParseExact() . I went tot he first search result, and then clicked the first link on the page to find the correct overload.

We see the second argument to that method (where you supplied "D" ) is a format string. The notes for that argument refer to the Remarks section, where we find this:

The format parameter is a string that contains either a single standard format specifier, or one or more custom format specifiers that define the required format of s. For details about valid formatting codes, see Standard Date and Time Format Strings or Custom Date and Time Format Strings .

Follow the link for the Standard Format Strings, and we finally find this information about the "D" format:

"D" Long date pattern. 2009-06-15T13:45:30 -> Monday, June 15, 2009 (en-US)

This is slightly confusing without the full context on the page, but what this tells you is it's expecting your dateOfBirth string to exactly match the pattern described by Monday, June 15, 2009 ( dddd, MMMM dd, yyyy ). Based on the previous question , your strings look more like 15-06-2009 ( dd-mm-yyyy ). Those don't match, and that's why you see the error.

To fix this, you need to find a format instead of "D" to use with the ParseExact() method that will exactly match the kind of format used with your input strings.

Again, this looks like a learning situation, so I'll leave it to you to figure that out.

Answer 2

Correct code.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DateEx1              //DO NOT CHANGE the namespace name
{
    public class Program       //DO NOT CHANGE the class name
    {
        public static void Main(string[] args)    //DO NOT CHANGE the 'Main' method signature
        {

             Console.WriteLine("Enter the date of birth (dd-mm-yyyy) ");
             string dateOfBirth=Console.ReadLine();
            Console.WriteLine(calculateAge(dateOfBirth));

        }

        public static int calculateAge(string dateOfBirth)
        {
            //Implement code here
            //int age;  
            DateTime s = DateTime.ParseExact(dateOfBirth, "dd-mm-yyyy",null);
            DateTime today = DateTime.Now;
            int year = DateTime.Now.Year;

            int length=dateOfBirth.Length;
            string dcs = dateOfBirth.Substring(6,4);
            string csd=dateOfBirth.Substring(3,2);
            int age2=int.Parse(csd);
            if(age2>=6)
            {
            int age=int.Parse(dcs);
            int age1=(year-1)-age;
            return age1;
            }
            else
            {
                 int age=int.Parse(dcs);
            int age3=(year)-age;
            return age3;
            }
        }

        }

    }