Question

Sample input string:

char *str = "12345.567675";

And the desired output if I need the precision of 3 places after decimal point:

str = "12345.568";

Is there a way to do this without converting the string to double and back to string?

Answer 1

yeah, on high level:
1. search ‘.’ in the string.
2. if the position of ‘.’ + 3 is smaller than the length you done.
3. otherwise, concat the string in the position of ‘.’ + 3.
4. here is tricky: you need to check the next char if exists, (‘.’ + 4), and if it’s value >= 5 goto 4.1 (otherwise goto 5)
4.1. copy the string to a new string that have one more space on the left (cause 9.9999 will be changed to 10.0000 in the ‘4’ loop) and set a pointer (P) to the last char in that string.
4.2. if *P between 0 to 8 add 1 to it and go to 5.
4.3. if *P is 9, set it to zero, move the pointer one left (-1) and goto 4.2
4.4. if *P is ‘.’, move the pointer one left (-1) and goto 4.2
5. remove all the 0 on the right of the decimal point (and the decimal point it self if needed) and you done!!!
6. delete everything, and use the double conversion method…