Question: ```
Str.replace(',','','');

```

I have to replace `(,)` with `(',')`

but in replace function we have to pass character in `' '` so it is giving me an error.

Answer: 
You just need to ensure your values are quoted properly:

```
String myString = "test, A";
myString.Replace(",", "','");

```
You don't have to pass characters in '' (as characters), you can also pass them as strings using "". That should solve your problem.

```
Str.Replace(",", "','");

```