Hi I've got this code for converting String to int manually.
int num = 0;
for(int i = 0; i < length(number); i++) {
num *= 10;
num += number.charAt(i) - '0';
println("i :" + num);
}
Why do we subtract '0' at the end?
Hi I've got this code for converting String to int manually.
int num = 0;
for(int i = 0; i < length(number); i++) {
num *= 10;
num += number.charAt(i) - '0';
println("i :" + num);
}
Why do we subtract '0' at the end?
The method .charAt(int position)
returns a single character from your number string. Since your string contains a number you will receive a character which contains a digit (0 - 9
). The next step would be to convert this character to an int.
a naive solution would be:
char digit = number.charAt(i);
if (digit == '0') {
num += 0;
} else if (digit == '1') {
num += 1;
}
But we can use the ASCII values of our characters to simplify this. Take a look at this ASCII table (only the columns 'Dec' and 'Chr'). You will see that the character 0
has in fact a value of 48. So if we substract 48 from our character we retrieve the correct value:
int num = digit - 48;
This can even be more simplified by directly placing the character which will be replaced by the compiler:
int num = digit - '0';
example:
character '4'
has an ASCII value of 52
. If we substract 48
we get 4 which is the wanted result.
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