Data · 11
Working with single characters
One character as a value: its code, letter arithmetic, the i-th character, repeating.
A single character is a value too.
Inside it is a number (its code), so you can add and subtract.
The example below reads a string like c2a3z1, where a lowercase letter and a digit alternate, two characters at a time and prints, on each line, the letter, its code, the next letter of the alphabet, and the letter repeated as many times as the digit says.
s = input()for i in range(0, len(s), 2): ch = s[i] # i번째 글자 count = int(s[i + 1]) # 숫자 글자 → 수 code = ord(ch) after = chr(ord("a") + (code - ord("a") + 1) % 26) # 다음 글자(z 다음은 a) print(ch, code, after, ch * count)const s = require("fs").readFileSync(0, "utf8").trim();const a = "a".charCodeAt(0);for (let i = 0; i < s.length; i += 2) { const ch = s[i]; // i번째 글자 const count = Number(s[i + 1]); // 숫자 글자 → 수 const code = ch.charCodeAt(0); const after = String.fromCharCode(a + ((code - a + 1) % 26)); // 다음 글자(z 다음은 a) console.log(ch, code, after, ch.repeat(count));}import { readFileSync } from "node:fs";const s: string = readFileSync(0, "utf8").trim();const a: number = "a".charCodeAt(0);for (let i = 0; i < s.length; i += 2) { const ch: string = s[i]; // i번째 글자 const count: number = Number(s[i + 1]); // 숫자 글자 → 수 const code: number = ch.charCodeAt(0); const after: string = String.fromCharCode(a + ((code - a + 1) % 26)); // 다음 글자(z 다음은 a) console.log(ch, code, after, ch.repeat(count));}import java.util.Scanner; public class Main { public static void main(String[] args) { String s = new Scanner(System.in).next(); for (int i = 0; i < s.length(); i += 2) { char ch = s.charAt(i); // i번째 글자 int count = s.charAt(i + 1) - '0'; // 숫자 글자 → 수 int code = ch; char after = (char) ('a' + (ch - 'a' + 1) % 26); // 다음 글자(z 다음은 a) System.out.println(ch + " " + code + " " + after + " " + String.valueOf(ch).repeat(count)); } }}using System; class Program{ static void Main() { string s = Console.ReadLine().Trim(); for (int i = 0; i < s.Length; i += 2) { char ch = s[i]; // i번째 글자 int count = s[i + 1] - '0'; // 숫자 글자 → 수 int code = ch; char after = (char)('a' + (ch - 'a' + 1) % 26); // 다음 글자(z 다음은 a) Console.WriteLine($"{ch} {code} {after} {new string(ch, count)}"); } }}#include <iostream>#include <string> int main() { std::string s; std::cin >> s; for (size_t i = 0; i < s.size(); i += 2) { char ch = s[i]; // i번째 글자 int count = s[i + 1] - '0'; // 숫자 글자 → 수 int code = ch; char after = 'a' + (ch - 'a' + 1) % 26; // 다음 글자(z 다음은 a) std::cout << ch << ' ' << code << ' ' << after << ' ' << std::string(count, ch) << '\n'; }}#include <stdio.h>#include <string.h> int main(void) { char s[101]; scanf("%100s", s); int len = strlen(s); for (int i = 0; i < len; i += 2) { char ch = s[i]; // i번째 글자 int count = s[i + 1] - '0'; // 숫자 글자 → 수 int code = ch; char after = 'a' + (ch - 'a' + 1) % 26; // 다음 글자(z 다음은 a) printf("%c %d %c ", ch, code, after); for (int k = 0; k < count; k++) putchar(ch); // 되풀이는 반복문으로 printf("\n"); } return 0;}s = Console.ReadLine().Trim();a = Str.Code("a");for (i = 0; i < s.Length; i += 2){ ch = s[i]; // i번째 글자 count = s[i + 1].ToNumber(); // 숫자 글자 → 수 code = Str.Code(ch); after = Str.FromCode(a + (code - a + 1) % 26); // 다음 글자(z 다음은 a) Console.WriteLine(ch + " " + code + " " + after + " " + ch.Repeat(count));}c2a3z1
c 99 d cc a 97 b aaa z 122 a z
Key points
- C, C++, Java and C# have a type
charthat holds exactly one character, written with single quotes ('a').
Python, JavaScript and Craykon have no such type: one character is just a string of length 1. - Letter arithmetic: the codes of the alphabet are consecutive (
a97,b98, …).
Soch - 'a'tells how many steps after a the letter is (0–25), and'a' + kis the letter k steps after a.
In languages withoutchar, convert to a code, calculate, then convert back to a character. - A digit character is not a number.
The code of'7'is 55.
To get the number 7, subtract the code of'0'('7' - '0') or use a to-number function. - Take the i-th character with
s[i](Java:s.charAt(i)).
The last character is atlength - 1.
Reading past it stops with an error in some languages, quietly givesundefinedin others, and in C and C++ is not checked at all, so what happens is not defined. - Repeating joins the same string n times.
"ab"three times is"ababab", and zero times is the empty string.
It lets you print stars or rules without a loop.
How each language writes it
| Python | Code ord(ch), back to a character chr(n) — the next letter is chr(ord(ch) + 1).Digit character: int(ch).s[i], and from the end s[-1].Out of range raises IndexError.Repeat: ch * 3 |
|---|---|
| JavaScript | Code ch.charCodeAt(0), back to a character String.fromCharCode(n).Digit character: Number(ch).s[i], and from the end s.at(-1).Out of range, s[9] is undefined with no error.Repeat: ch.repeat(3) |
| TypeScript | Same as JavaScript |
| Java | char ch = s.charAt(i) — s[i] is not allowed.Code: int code = ch; back to a character: (char) (ch + 1).Digit character: ch - '0'.Out of range throws StringIndexOutOfBoundsException.Only strings can repeat: String.valueOf(ch).repeat(3) |
| C# | char ch = s[i], last is s[^1].Code: int code = ch; back to a character: (char)(ch + 1).Digit character: ch - '0'.Out of range throws IndexOutOfRangeException.Repeat a character: new string(ch, 3) |
| C++ | char ch = s[i] — a char is simply a small integer, so ch + 1 and ch - '0' work directly.s[i] does not check the range, so reading an index greater than the length is undefined behaviour (a garbage value or a crash); s.at(i) checks and throws std::out_of_range.Repeat a character: std::string(3, ch) (count first) |
| C | char ch = s[i] — as in C++, a char is a small integer.In printf, %c prints it as a character and %d as its code.s[length] holds the end marker \0; reading beyond that is not checked and is undefined behaviour (a garbage value or a crash).There is no repeat, so print in a loop |
| Craykon | Code Str.Code(ch), back to a character Str.FromCode(n).Digit character: ch.ToNumber().s[i] — out of range stops with the error "string only has indexes 0–2" (negative indexes too).Repeat: ch.Repeat(3) |
Common mistakes
Adding 1 to a one-character stringPython · JavaScript · TypeScript · Craykon
print("a" + 1)→ Python raises TypeError: can only concatenate str (not "int") to str. JavaScript, TypeScript and Craykon give a1 with no error — the number is appended
Convert to a code, add, and convert back: Python chr(ord("a") + 1), JavaScript String.fromCharCode("a".charCodeAt(0) + 1), Craykon Str.FromCode(Str.Code("a") + 1).
Adding 1 to a character and printing it gave a numberJava · C# · C++
System.out.println('a' + 1); // Java
Console.WriteLine('a' + 1); // C#
std::cout << 'a' + 1; // C++→ All three print 98 — adding a number to a char gives an int
Convert back to a character: (char) ('a' + 1) → b.
For the same reason, char c = 'a'; c = c + 1; is a compile error in Java and C#; write c++ or c = (char) (c + 1).
Using a digit character as if it were the numberC · C++ · Java · C#
char ch = '7';
int n = ch;
printf("%d\n", n);→ 55 — not 7 but the code of '7'
Subtract '0': ch - '0' → 7.
It works because the codes of the digit characters are consecutive, starting at '0' (48).
How languages differ
Repeating is easy to confuse with multiplying.
In Python
JavaScript goes the other way (
In C++
Swap them into
Repeating is easy to confuse with multiplying.
In Python
"3" * 2 is "33", not 6, so multiplying input you forgot to convert repeats the string instead.JavaScript goes the other way (
"3" * 2 is 6), TypeScript gives a compile error, and Craykon stops with "* only works on two numbers".In C++
std::string(3, '*') takes the count first.Swap them into
std::string('*', 3) and you get, with no error, a wrong 42-character string (the code of '*' is 42).