s := "123"
out := 0
for _, ch := range s {
if ch < '0' || ch > '9' {
panic("invalid character")
digit := int(ch - '0')
out = out*10 + digit

This Go code converts a string of digits into an integer value. Here’s how it works:

1. A string s containing the digits to be converted is defined and initialized with the value “123”.

2. An integer variable out is defined and initialized with the value 0. This variable will hold the result of the conversion.

3. A for loop is used to iterate over each character in the string s. The range keyword is used to iterate over the string as a collection of Unicode code points (which is equivalent to iterating over the string character by character).

4. Inside the loop, the current character ch is checked to ensure that it is a digit between ‘0’ and ‘9’. If it is not, the program panics with an error message.

5. If the character is a valid digit, it is converted to an integer value by subtracting the ASCII value of ‘0’ from it. This works because the ASCII codes for the digits ‘0’ to ‘9’ are contiguous, with ‘0’ having the smallest code.

6. The integer value of the digit is then added to the out variable. To do this, the previous value of out is multiplied by 10 (to shift the existing digits left by one place), and the digit value is added.

7. After the loop completes, the out variable will contain the integer value of the string “123”, which is 123.

8. Finally, the fmt.Println function is used to print the value of out to the console.

So, the output of this code is 123.



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