Change part of one string.

[GiovanniHDZ]

Hi developers!

I have one string of my database, I use this to read if the user has a item.
The string its “0000000”

If the user has the object with IDObject 3 and the object with IDObject 5 so the string its “0010100”
I can read this from database, but I don’t know how to modify part of the string to update the data.

I think in one function like this.

void PurchaseCard(int Card){
//when I call the function I want to make the entry number
//find this position in the string to change the number 0 to 1
string X = 1;
//Get the position 6 on my string and modify them like this
StringDB = "00000X0";
NewString = "0000010"; //And with this I can send to the DB
}
PurchaseCard(6)

[Kurt-Dekker]

Strings are immutable in C# so what you do is chop off the first part, put in your 1, and then add your last part, making a new string.

Off the top of my head:

int Card =  ???;

string data = "00000000";   // how it comes out of the database

// chop chop chop
data = data.Substring( 0, Card - 1) + "1" + data.Substring( Card + 1);

That might be off by one, I just typed it, didn’t run it. Verify with some graph paper and some numbers…

Be aware also:

• be consistent which side is the lowest value (left endian or right endian)

• be consistent whether the lowest value is 0 or 1. Tradition favors 0 as “the first card” but your code looks like it might be 1-based.

ALL OF THAT being said, it might be better to have a generic “load from the database” function that returns an array of booleans, and then you set/clear the boolean at the index you care about, then you have another function that sticks that array back into the database, making it a string first. If you hide all that in one part of your code, you can later change it without much fuss.

[GiovanniHDZ]

@Kurt-Dekker

Strings are immutable in C# so what you do is chop off the first part, put in your 1, and then add your last part, making a new string.

Off the top of my head:

int Card =  ???;

string data = "00000000";   // how it comes out of the database

// chop chop chop
data = data.Substring( 0, Card - 1) + "1" + data.Substring( Card + 1);

That might be off by one, I just typed it, didn’t run it. Verify with some graph paper and some numbers…

Be aware also:

• be consistent which side is the lowest value (left endian or right endian)

• be consistent whether the lowest value is 0 or 1. Tradition favors 0 as “the first card” but your code looks like it might be 1-based.

ALL OF THAT being said, it might be better to have a generic “load from the database” function that returns an array of booleans, and then you set/clear the boolean at the index you care about, then you have another function that sticks that array back into the database, making it a string first. If you hide all that in one part of your code, you can later change it without much fuss.

Thanks, I’m thinking on use substring function and get 2 strings and add the STRING 1 in the middle of the 2 created strings and get the final string with this

[Ardenian]

@GiovanniHDZ

Thanks, I’m thinking on use substring function and get 2 strings and add the STRING 1 in the middle of the 2 created strings and get the final string with this

StringBuilder is recommended for these operations. From the outside, it allows you to dynamically build your string.

(…) Although StringBuilder and String both represent sequences of characters, they are implemented differently. String is an immutable type. That is, each operation that appears to modify a String object actually creates a new string. (…) The alternative is to use StringBuilder, which is a mutable string class. Mutability means that once an instance of the class has been created, it can be modified by appending, removing, replacing, or inserting characters. (…)

[Madgvox]

If you’re saving the item state as a bitmask, why not store the field as an integer and read/set the values directly using bitwise operations? If you have more than 32 items, you probably would want a more comprehensive structure than just a bitmask anyway.

Or if you’re stuck using a string, you can convert it to an int from binary using the Convert class, then convert it back once you’re done manipulating it.