How do I add "123" to the beginning of a string and pad it to be exactly 12 chars?

I need to add "开发者_如何学Go123" and zeros for any string - but the resulting string must be exactly 12 characters long.

For example:

28431 = 123000028431
987   = 123000000987
2     = 123000000002

How to do this in C#?

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Well, you could use:

string result = "123" + text.PadLeft(9, '0');

In other words, split the task in half - one part generating the "000028431", "000000987" etc part using string.PadLeft, and the other prefixing the result with "123" using simple string concatenation.

There are no doubt more efficient approaches, but this is what I'd do unless I had a good reason to believe that efficiency was really important for this task.

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var result = string.Format("123{0}", number.PadLeft(9, '0'));

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You could try:

var str = String.Format("123{0:0#########}", 28431);

or

var str = String.Format("123{0:000000000}", 28431);

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Well, if you have numbers less than 1000000000, you could just add 123000000000 to each number.

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Assuming...

1. The strings are known to always contain representations of decimal integers.
2. The represented integer is always less than 10⁹.

...you could do this:

(123000000000 + long.Parse(s)).ToString()

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try this code

            string argString ="28431 ";

            StringBuilder sb =new StringBuilder();
            sb.Append(argString);
            for (int i =  12 -argString.Length-3; i >0 ; i--)
            {
                 sb.Insert(0, "0");              
            }

            string result = string.Format("123{0}",sb.ToString());