C# convert int to string with padding zeros?

Question

In C# I have an integer value which need to be convereted to string but it needs to add zeros before:

For Example:

int i = 1;

When

Answer 1

public static string ToLeadZeros(this int strNum, int num)
{
    var str = strNum.ToString();
    return str.PadLeft(str.Length + num, '0');
}

// var i = 1;
// string num = i.ToLeadZeros(5);

Answer 2

Easy peasy

int i = 1;
i.ToString("0###")

Answer 3

.NET has an easy function to do that in the String class. Just use:

.ToString().PadLeft(4, '0')  // that will fill your number with 0 on the left, up to 4 length

int i = 1; 
i.toString().PadLeft(4,'0')  // will return "0001"  

Answer 4

Here's a good example:

int number = 1;
//D4 = pad with 0000
string outputValue = String.Format("{0:D4}", number);
Console.WriteLine(outputValue);//Prints 0001
//OR
outputValue = number.ToString().PadLeft(4, '0');
Console.WriteLine(outputValue);//Prints 0001 as well

Answer 5

Here I want to pad my number with 4 digit. For instance, if it is 1 then it should show as 0001, if it 11 it should show as 0011.

Below is the code that accomplishes this:

reciptno=1; // Pass only integer.

string formatted = string.Format("{0:0000}", reciptno);

TxtRecNo.Text = formatted; // Output=0001

I implemented this code to generate money receipt number for a PDF file.

Answer 6

i.ToString().PadLeft(4, '0') - okay, but doesn't work for negative numbers
i.ToString("0000"); - explicit form
i.ToString("D4"); - short form format specifier
$"{i:0000}"; - string interpolation (C# 6.0+)