for_loop/Program.cs

using System;

class Program {
	static int Main(string[] args) {
		// 1.
		{
			Console.Write("E1: Enter string [+-0]: ");
			string str = Console.ReadLine();
			int x = 1;
			foreach (char c in str) switch (c) {
				case '+': ++x;   break;
				case '-': --x;   break;
				case '0': x = 0; break;
				default:
					Console.WriteLine("Invalid character: '"+c+"'!");
					return 1;
			}
			Console.WriteLine(x);
		}
		// 2.
		{
			Console.Write("E2: Enter string [+-0!]: ");
			string str = Console.ReadLine();
			int x = 1;
			foreach (char c in str) switch (c) {
				case '+': ++x;   break;
				case '-': --x;   break;
				case '0': x = 0; break;
				case '!':
					if (x == 0) break;
					int s = x < 0 ? 1 : -1;
					for (int i = x+s; i != 0; i += s) x *= i;
					break;
				default:
					Console.WriteLine("Invalid character: '"+c+"'!");
					return 1;
			}
			Console.WriteLine(x);
		}
		// 3.
		{
			Console.Write("E3: Enter a word: ");
			string str = Console.ReadLine();
			for (int i = 0; i < str.Length; i += 2)
				Console.Write(str[i]);
			Console.WriteLine();
		}
		// 4.
		{
			Console.Write("E4: Enter words: ");
			string str = Console.ReadLine();
			string[] split = str.Split(' ');
			for (int i = 0; i < split.Length; i += 2)
				Console.Write(split[i] + ' ');
			Console.WriteLine();
		}

		return 0;
	}
}