RegEx for string以数字开头，后跟字母

Question

I want Regular expression for such inputs.

1
1a
1b
1c
1d
2
2a
2b
2c

But if i write following inputs then it should not allow.

a
b
c

The string must start with 1 or 2 (only once and mandatory) and then followed by any character between a to z(only once)

So total string length is 2 only

the first letter will be always 1 or 2 (first letter is mandatory)
second letter will be a to z (not mandatory)

I tried this [1-2]?[a-zA-Z]? but it allow me to enter string starts with any character..

I want this RegEx for C#.Net

Answer 1

You need to anchor the regular expression - you need to specify that they need to be at the start of the string.

You also need to specify that 1 or 2 has to be there. There are several ways to do so, I chose alternation (1|2) , thought the character class is another option ( [12] ).

You do that by starting the regex with ^ :

^(1|2)[a-zA-Z]?

So, the above will match

Answer 2

这样做^(1|2)[a-zA-Z]?$