1) Input text
2) Compare each character with:
    letter
    punctuation
3) Output with changes

using System;
using System.Collections.Generic;
namespace AntiCAPS {
    public class Program {
        public static void Main(string[] args) {
            bool _newSentence = true;
            string message = Console.In.ReadToEnd().ToLower();
            List<char> punctuation = new List<char>(new char[] { '!', '.', '?' });
            for (int iterable = 0; iterable < message.Length; iterable++) {
                if ((int)message[iterable] >= 97 && (int)message[iterable] <= 122) {
                    if (_newSentence) {
                        Console.Write(Char.ToUpper(message[iterable]));
                        _newSentence = false;
                    } else Console.Write(message[iterable]);
                } else if (punctuation.Contains(message[iterable])) {
                    _newSentence = true;
                    Console.Write(message[iterable]);
                } else Console.Write(message[iterable]);
            }
        }
    }
}

Edited by author 02.11.2021 00:10