• 2022年6月29日--使用C#迈出第一步--使用 C# 中的“if”、“else”和“else if”语句向代码添加决策逻辑

    了解如何通过评估布尔表达式来为代码的执行路径创建分支。

    简介

    通过 C# 编程语言，你可以构建采用决策逻辑的应用程序。 通过分支逻辑，你的应用程序可根据一组条件执行不同的指令。

    使用if语句

    运用最广泛的分支语句是 if 语句。 if 语句依赖布尔表达式，后者用一组括号括起来。 如果表达式为 true，则执行 if 语句后面的代码。 如果表达式为 false，则跳过 if 语句后面的代码。

    使用if语句创建随机数游戏

    我们将使用 Random.Next() 方法来模拟抛掷三个六面骰子。

    • 如果抛掷任何两个骰子得到相同的值，则因两个骰子投出同样的点数获得两点奖励得分。
    • 如果抛掷全部三个骰子都得到相同的值，则因三个骰子投出同样的点数获得六点奖励得分。
    • 如果三个骰子投出的点数之和加上所有奖励点数大于等于 15，则你赢得比赛。 否则，就是你输了。

    步骤1-编写代码以生成三个随机数字并在输出中显示它们

    1. Random dice = new Random();
    2.  
    3. int roll1 = dice.Next(1, 7);
    4. int roll2 = dice.Next(1, 7);
    5. int roll3 = dice.Next(1, 7);
    6.  
    7. int total = roll1 + roll2 + roll3;
    8.  
    9. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");

    Dice roll: 2 + 2 + 2 = 6

    步骤2-添加一个if语句，以基于total变量的值显示不同的消息

    1. Random dice = new Random();
    2.  
    3. int roll1 = dice.Next(1, 7);
    4. int roll2 = dice.Next(1, 7);
    5. int roll3 = dice.Next(1, 7);
    6.  
    7. int total = roll1 + roll2 + roll3;
    8.  
    9. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");
    10.  
    11. if (total > 14)
    12. {
    13.     Console.WriteLine("You win!");
    14. }
    15.  
    16. if (total < 15)
    17. {
    18.     Console.WriteLine("Sorry, you lose.");
    19. }

    1. Dice roll: 5 + 5 + 3 = 13
    2. Sorry, you lose.

    什么是布尔表达式？

    布尔表达式是返回布尔值（true 或 false）的任意代码。

    string.Contains() 方法计算某个字符串是否包含另一个字符串

    1. string message = "The quick brown fox jumps over the lazy dog.";
    2. bool result = message.Contains("dog");
    3. Console.WriteLine(result);
    4.  
    5. if (message.Contains("fox"))
    6. {
    7.     Console.WriteLine("What does the fox say?");
    8. }

    1. True
    2. What does the fox say?

    什么是代码块？

    步骤3-再添加一个if语句来实现双倍奖励

    1. Random dice = new Random();
    2.  
    3. int roll1 = dice.Next(1, 7);
    4. int roll2 = dice.Next(1, 7);
    5. int roll3 = dice.Next(1, 7);
    6.  
    7. int total = roll1 + roll2 + roll3;
    8.  
    9. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");
    10.  
    11. if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
    12. {
    13.     Console.WriteLine("You rolled doubles! +2 bonus to total!");
    14.     total += 2;
    15. }
    16.  
    17. if (total >= 15)
    18. {
    19.     Console.WriteLine("You win!");
    20. }
    21.  
    22. if (total < 15)
    23. {
    24.     Console.WriteLine("Sorry, you lose.");
    25. }

    1. Dice roll: 3 + 6 + 5 = 14
    2. Sorry, you lose.

    步骤4-再添加一个if语句来实现三倍奖励

    1. Random dice = new Random();
    2.  
    3. int roll1 = dice.Next(1, 7);
    4. int roll2 = dice.Next(1, 7);
    5. int roll3 = dice.Next(1, 7);
    6.  
    7. int total = roll1 + roll2 + roll3;
    8.  
    9. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");
    10.  
    11. if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
    12. {
    13.     Console.WriteLine("You rolled doubles! +2 bonus to total!");
    14.     total += 2;
    15. }
    16.  
    17. if ((roll1 == roll2) && (roll2 == roll3)) 
    18. {
    19.     Console.WriteLine("You rolled triples! +6 bonus to total!");
    20.     total += 6;
    21. }
    22.  
    23. if (total >= 15)
    24. {
    25.     Console.WriteLine("You win!");
    26. }
    27.  
    28. if (total < 15)
    29. {
    30.     Console.WriteLine("Sorry, you lose.");
    31. }

    1. Dice roll: 1 + 1 + 5 = 7
    2. You rolled doubles! +2 bonus to total!
    3. Sorry, you lose.

    逻辑上的问题以及改进代码的机会

    回顾

    使用“else”和“else if”语句

    通过添加else和else if语句来改进代码并修复bug

    1. Random dice = new Random();
    2.  
    3. int roll1 = dice.Next(1, 7);
    4. int roll2 = dice.Next(1, 7);
    5. int roll3 = dice.Next(1, 7);
    6.  
    7. int total = roll1 + roll2 + roll3;
    8.  
    9. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");
    10.  
    11. if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
    12. {
    13.     Console.WriteLine("You rolled doubles!  +2 bonus to total!");
    14.     total += 2;
    15. }
    16.  
    17. if ((roll1 == roll2) && (roll2 == roll3))
    18. {
    19.     Console.WriteLine("You rolled triples!  +6 bonus to total!");
    20.     total += 6;
    21. }
    22.  
    23. if (total >= 15)
    24. {
    25.     Console.WriteLine("You win!");
    26. }
    27. else 
    28. {
    29.     Console.WriteLine("Sorry, you lose.");
    30. }

    1. Dice roll: 5 + 1 + 4 = 10
    2. Sorry, you lose.

    步骤1-使用if和else语句，而不是两个单独的if语句

    1. int roll1 = 6;
    2. int roll2 = 6;
    3. int roll3 = 6;
    4.  
    5. int total = roll1 + roll2 + roll3;
    6.  
    7. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");
    8.  
    9. if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
    10. {
    11.     if ((roll1 == roll2) && (roll2 == roll3))
    12.     {
    13.         Console.WriteLine("You rolled triples!  +6 bonus to total!");
    14.         total += 6;
    15.     }
    16.     else
    17.     {
    18.         Console.WriteLine("You rolled doubles!  +2 bonus to total!");
    19.         total += 2;
    20.     }
    21. }
    22.  
    23. if (total >= 15)
    24. {
    25.     Console.WriteLine("You win!");
    26. }
    27. else 
    28. {
    29.     Console.WriteLine("Sorry, you lose.");
    30. }

    1. Dice roll: 6 + 6 + 6 = 18
    2. You rolled triples!  +6 bonus to total!
    3. You win!

    步骤2-使用嵌套消除双倍奖励和三倍奖励叠加的情形

     玩家应该只赢取一个奖品：

    • 如果玩家的分数大于等于 16，则赢得一辆新车。
    • 如果玩家的分数大于等于 10，则赢得一台新的笔记本电脑。
    • 如果玩家的分数正好为 7，则赢得一次旅行机会。
    • 否则，玩家赢得一只小猫。

    1. Random dice = new Random();
    2.  
    3. int roll1 = dice.Next(1, 7);
    4. int roll2 = dice.Next(1, 7);
    5. int roll3 = dice.Next(1, 7);
    6.  
    7. int total = roll1 + roll2 + roll3;
    8.  
    9. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");
    10.  
    11. if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
    12. {
    13.     if ((roll1 == roll2) && (roll2 == roll3))
    14.     {
    15.         Console.WriteLine("You rolled triples!  +6 bonus to total!");
    16.         total += 6;
    17.     }
    18.     else
    19.     {
    20.         Console.WriteLine("You rolled doubles!  +2 bonus to total!");
    21.         total += 2;
    22.     }
    23. }
    24.  
    25. if (total >= 16)
    26. {
    27.     Console.WriteLine("You win a new car!");
    28. }
    29. else if (total >= 10)
    30. {
    31.     Console.WriteLine("You win a new laptop!");
    32. }
    33. else if (total == 7)
    34. {
    35.     Console.WriteLine("You win a trip for two!");
    36. }
    37. else
    38. {
    39.     Console.WriteLine("You win a kitten!");
    40. }

    1. Dice roll: 1 + 5 + 1 = 7
    2. You rolled doubles!  +2 bonus to total!
    3. You win a kitten!

    步骤3-使用if、else和else if语句提供奖励，而不是显示胜败消息

     玩家应该只赢取一个奖品：

    • 如果玩家的分数大于等于 16，则赢得一辆新车。
    • 如果玩家的分数大于等于 10，则赢得一台新的笔记本电脑。
    • 如果玩家的分数正好为 7，则赢得一次旅行机会。
    • 否则，玩家赢得一只小猫。

    1. Random dice = new Random();
    2.  
    3. int roll1 = dice.Next(1, 7);
    4. int roll2 = dice.Next(1, 7);
    5. int roll3 = dice.Next(1, 7);
    6.  
    7. int total = roll1 + roll2 + roll3;
    8.  
    9. Console.WriteLine($"Dice roll: {roll1} + {roll2} + {roll3} = {total}");
    10.  
    11. if ((roll1 == roll2) || (roll2 == roll3) || (roll1 == roll3))
    12. {
    13.     if ((roll1 == roll2) && (roll2 == roll3))
    14.     {
    15.         Console.WriteLine("You rolled triples!  +6 bonus to total!");
    16.         total += 6;
    17.     }
    18.     else
    19.     {
    20.         Console.WriteLine("You rolled doubles!  +2 bonus to total!");
    21.         total += 2;
    22.     }
    23. }
    24.  
    25. if (total >= 16)
    26. {
    27.     Console.WriteLine("You win a new car!");
    28. }
    29. else if (total >= 10)
    30. {
    31.     Console.WriteLine("You win a new laptop!");
    32. }
    33. else if (total == 7)
    34. {
    35.     Console.WriteLine("You win a trip for two!");
    36. }
    37. else
    38. {
    39.     Console.WriteLine("You win a kitten!");
    40. }

    回顾

    挑战

    1. Random random = new Random();
    2. int daysUntilExpiration = random.Next(12);
    3. int discountPercentage = 0;
    4.  
    5. // Your code goes here
    6.  
    7. Console.WriteLine(daysUntilExpiration);
    8. if(daysUntilExpiration==1)
    9. {
    10.     discountPercentage=20;
    11.     Console.WriteLine("Your subscription expires within a day!");
    12.     Console.WriteLine("Renew now and save {0}%!",discountPercentage);
    13. }
    14. else if(daysUntilExpiration>1&&daysUntilExpiration<=5)
    15. {
    16.     discountPercentage=10;
    17.     Console.WriteLine("Your subscription expires in {0} days.",daysUntilExpiration);
    18.     Console.WriteLine("Renew now and save {0}%!",discountPercentage);
    19. }
    20. else if(daysUntilExpiration<=10)
    21. {
    22.     Console.WriteLine("Your subscription will expire soon. Renew now!");
    23. }
    24. else
    25. {
    26.     Console.WriteLine("Your subscription has expired.");
    27. }

    1. 9
    2. Your subscription will expire soon. Renew now!

    1. 11
    2. Your subscription has expired.

    1. 5
    2. Your subscription expires in 5 days.
    3. Renew now and save 10%!

    解决方案：

    1. Random random = new Random();
    2. int daysUntilExpiration = random.Next(12);
    3. int discountPercentage = 0;
    4.  
    5. if (daysUntilExpiration == 0)
    6. {
    7.     Console.WriteLine("Your subscription has expired.");
    8. }
    9. else if (daysUntilExpiration == 1)
    10. {
    11.     Console.WriteLine("Your subscription expires within a day!");
    12.     discountPercentage = 20;
    13. }
    14. else if (daysUntilExpiration <= 5)
    15. {
    16.     Console.WriteLine($"Your subscription expires in {daysUntilExpiration} days.");
    17.     discountPercentage = 10;
    18. }
    19. else if (daysUntilExpiration <= 10)
    20. {
    21.     Console.WriteLine("Your subscription will expire soon. Renew now!");
    22. }
    23.  
    24. if (discountPercentage > 0)
    25. {
    26.     Console.WriteLine($"Renew now and save {discountPercentage}%.");
    27. }

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  • 原文地址：https://blog.csdn.net/DXB2021/article/details/125528597