A general console application programs

Day 1- Try to practice

listing 1
/*
   This is a simple C# program.

   Call this program Example.cs.
*/

using System;

class Example {

  // A C# program begins with a call to Main().
  public static void Main() {
    Console.WriteLine("A simple C# program.");
  }
}

listing 2
// This version does not include the using System statement.

class Example {

  // A C# program begins with a call to Main().
  public static void Main() {

    // Here, Console.WriteLine is fully qualified.
    System.Console.WriteLine("A simple C# program.");
  }
}

listing 3
// This program demonstrates variables.

using System;

class Example2 {
  public static void Main() {
    int x; // this declares a variable
    int y; // this declares another variable

    x = 100; // this assigns 100 to x

    Console.WriteLine("x contains " + x);

    y = x / 2;

    Console.Write("y contains x / 2: ");
    Console.WriteLine(y);
  }
}

listing 4
/*
   This program illustrates the differences
   between int and double.
*/

using System;

class Example3 {
  public static void Main() {
    int ivar;     // this declares an int variable
    double dvar;  // this declares a floating-point variable

    ivar = 100;   // assign ivar the value 100
 
    dvar = 100.0; // assign dvar the value 100.0

    Console.WriteLine("Original value of ivar: " + ivar);
    Console.WriteLine("Original value of dvar: " + dvar);

    Console.WriteLine(); // print a blank line

    // now, divide both by 3
    ivar = ivar / 3;
    dvar = dvar / 3.0;

    Console.WriteLine("ivar after division: " + ivar);
    Console.WriteLine("dvar after division: " + dvar);
  }
}

listing 5
// Compute the area of a circle.

using System;
 
class Circle {
  static void Main() {
    double radius;
    double area;

    radius = 10.0;
    area = radius * radius * 3.1416;

    Console.WriteLine("Area is " + area);
  }
}

listing 6
// Demonstrate the if.

using System;

class IfDemo {
  public static void Main() {
    int a, b, c;

    a = 2;
    b = 3;

    if(a < b) Console.WriteLine("a is less than b");

    // this won't display anything
    if(a == b) Console.WriteLine("you won't see this");

    Console.WriteLine();

    c = a - b; // c contains -1

    Console.WriteLine("c contains -1");
    if(c >= 0) Console.WriteLine("c is non-negative");
    if(c < 0) Console.WriteLine("c is negative");

    Console.WriteLine();

    c = b - a; // c now contains 1
    Console.WriteLine("c contains 1");
    if(c >= 0) Console.WriteLine("c is non-negative");
    if(c < 0) Console.WriteLine("c is negative");

  }
}

listing 7
// Demonstrate the for loop.

using System;

class ForDemo {
  public static void Main() {
    int count;

    for(count = 0; count < 5; count = count+1)
      Console.WriteLine("This is count: " + count);

    Console.WriteLine("Done!");
  }
}

listing 8
// Demonstrate a block of code.

using System;

class BlockDemo {
  public static void Main() {
    int i, j, d;

    i = 5;
    j = 10;

    // the target of this if is a block
    if(i != 0) {
      Console.WriteLine("i does not equal zero");
      d = j / i;
      Console.WriteLine("j / i is " + d);
    }
  }
}

listing 9
// Compute the sum and product of the numbers from 1 to 10.

using System;
 
class ProdSum {
  static void Main() {
    int prod;
    int sum;
    int i;

    sum = 0;
    prod = 1;

    for(i=1; i <= 10; i++) {
      sum = sum + i;
      prod = prod * i;    
    }
    Console.WriteLine("Sum is " + sum);
    Console.WriteLine("Product is " + prod);

  }
}

listing 10
// Demonstrate an @ identier.

using System;
 
class IdTest {
  static void Main() {
    int @if; // use if as an identifier

    for(@if = 0; @if < 10; @if++)
      Console.WriteLine("@if is " + @if);
  }
}