Replace a Character At a Specific Index in a String

Replace a character at a specific index in a string?

String are immutable in Java. You can't change them.

You need to create a new string with the character replaced.

String myName = "domanokz";
String newName = myName.substring(0,4)+'x'+myName.substring(5);

Or you can use a StringBuilder:

StringBuilder myName = new StringBuilder("domanokz");
myName.setCharAt(4, 'x');

System.out.println(myName);

How do I replace a character at a particular index in JavaScript?

In JavaScript, strings are immutable, which means the best you can do is to create a new string with the changed content and assign the variable to point to it.

You'll need to define the replaceAt() function yourself:

String.prototype.replaceAt = function(index, replacement) {
    return this.substring(0, index) + replacement + this.substring(index + replacement.length);
}

And use it like this:

var hello = "Hello World";
alert(hello.replaceAt(2, "!!")); // He!!o World

How to replace one character at a specific index in a string

"So for a more concrete example, this is what I have and what I want to do: ...

... So is there any other way I can do this, or help me understand why I'm getting a seg fault?"

//I want to do this
input.at(2) = "a"; //obviously this doesn't work

It doesn't work, because "a" actually provides a const char* pointer, and not a char as required by std::string::at().

Use a simple character literal, not a c-style string literal:

 input.at(2) = 'a';
            // ^^^

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"When I try input.insert(2,a);, and cout << input I get bb$bbbbb followed by a seg fault message on the next line."

Besides std::string::insert() doesn't provide replacement of a character at the given position, but inserts one or more characters there, you may have an uninitialized char* a passed here, causing a segfault. But to answer this part finally, you should specify what the variable a actually is in this context.

Replacing a char at a given index in string?

Use a StringBuilder:

StringBuilder sb = new StringBuilder(theString);
sb[index] = newChar;
theString = sb.ToString();

How do I replace a string at a index in python?

Without creating a list you could also do:

i = "hello!"
i = "H" + i[1:]

More general:

def change_letter(string, letter, index):  # note string is actually a bad name for a variable
    return string[:index] + letter + string[index+1:]

s = "hello!"
s_new = change_letter(s, "H", 0)
print(s_new)
# should print "Hello!"

Also note there is a built in function .capitalize()

How do I change characters at a specific index within a string in rust?

The easiest way is to use the replace_range() method like this:

let mut hello = String::from("hello world");
hello.replace_range(3..4,"x");
println!("hello: {}", hello);

Output: hello: helxo world (Playground)

Please note that this will panic if the range to be replaced does not start and end on UTF-8 codepoint boundaries. E.g. this will panic:

let mut hello2 = String::from("hell world");
hello2.replace_range(4..5,"x"); // panics because needs more than one byte in UTF-8

If you want to replace the nth UTF-8 code point, you have to do something like this:

pub fn main() {
    let mut hello = String::from("hell world");
    hello.replace_range(
        hello
            .char_indices()
            .nth(4)
            .map(|(pos, ch)| (pos..pos + ch.len_utf8()))
            .unwrap(),
        "x",
    );
    println!("hello: {}", hello);
}

(Playground)

How to replace a character in a string using index in clojure

Like almost everything commonly used in Clojure, strings are immutable, so you need to create a new string with the new character in place of the old at the desired location:

(defn replace-at [s idx replacement]
  (str (subs s 0 idx) replacement (subs s (inc idx))))

> (replace-at "012345" 2 "x")
01x345

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