Add zero before number if less than 10

To add zero in our string or integer if value is less than 10, can be achieved in several ways, like:

int testNumber = 9;

// 1: just stick a zero before it

string sFormatted1 = string.Format("0{0}", testNumber );

// 2: use a special format string to use at least two digits

string sFormatted12 = string.Format("{0:00}", testNumber );

// 3: pad the string with zeros to the left

string sFormatted3 = testNumber .PadLeft(2, '0');

// 4: manually concatenate with "0"

string sFormatted4 = "0" + testNumber ;