## How Can I Convert Lowercase Characters to Uppercase in a Go String?

Altering Strings in Go

Q: I want to convert lowercase characters to uppercase in a string, but Go throws an error: "cannot assign to new_str[i]". How can I achieve this?

A: Understanding Go String Immutability

In Go, strings are immutable, meaning once created, their contents cannot be modified. This behavior aligns with the Go Language Specification, which states:

"Strings are immutable: once created, it is impossible to change the contents of a string."

A: Working Around String Immutability

To modify a string in Go, you have two options:

1. Cast the string to a []byte slice and alter the slice.
2. Create a new string with the desired modifications.

A: Altering Strings Using []byte Slices

Here is a modified version of your code that uses a []byte slice to alter the characters.

<code class="go">package main

import (
    "bytes"
    "fmt"
)

func ToUpper(str string) string {
    strBytes := []byte(str)
    for i := 0; i < len(str); i++ {
        if str[i] >= 'a' && str[i] <= 'z' {
            chr := uint8(rune(str[i]) - 'a' + 'A')
            strBytes[i] = chr
        }
    }
    return string(strBytes)
}

func main() {
    fmt.Println(ToUpper("cdsrgGDH7865fxgh"))
}
</code>

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