July 31, 2022 -- Take your first steps with C# -- Use arrays and foreach statements in C# to store and iterate through sequences of data

Process related sequences of data in a data structure called arrays. 然后,Learn how to iterate through each item in a sequence.

简介

C# Arrays can store sequences of values ​​in a single data structure. 换而言之,Suppose a variable that can hold multiple values. Once you have a variable that can store all the values,to sort the values、Reverse the order of values、Iterate over each value and check each value one by one,等等.

练习-Array basic information

什么是数组？

An array is a series of individual data elements accessible through a single variable name. Access each element in the array using a zero-based numeric index.

声明数组

Arrays are a special type of variable,Multiple values ​​of the same data type can be saved. Because the data type and size of the array must be specified at the same time,So the declaration syntax is slightly different.

步骤1-声明新数组

new The operator creates a new instance of the array in computer memory that can hold three string values. 

string[] fraudulentOrderIDs = new string[3];

为数组的元素赋值

此时,We have declared an array of strings,But every element of that array is empty. To access elements of an array,Please use a zero-based numeric index within square brackets.

like regular variables,使用 = Assign values ​​to assign values.

步骤2-为数组中的元素赋值

string[] fraudulentOrderIDs = new string[3];

fraudulentOrderIDs[0] = "A123";
fraudulentOrderIDs[1] = "B456";
fraudulentOrderIDs[2] = "C789";

步骤3-Attempt to use an index outside the bounds of the array

Access each element in the array starting at zero. 

string[] fraudulentOrderIDs = new string[3];

fraudulentOrderIDs[0] = "A123";
fraudulentOrderIDs[1] = "B456";
fraudulentOrderIDs[2] = "C789";
fraudulentOrderIDs[3] = "D000";

运行应用时,Received a long error message.

System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.IndexOutOfRangeException: Index was outside the bounds of the array.

Get the value of an element in an array

Values ​​can be obtained from elements of an array in the same way. Use the element's index to retrieve the element's value.

步骤4-Retrieve the value of an array

string[] fraudulentOrderIDs = new string[3];

fraudulentOrderIDs[0] = "A123";
fraudulentOrderIDs[1] = "B456";
fraudulentOrderIDs[2] = "C789";
// fraudulentOrderIDs[3] = "D000";

Console.WriteLine($"First: {fraudulentOrderIDs[0]}");
Console.WriteLine($"Second: {fraudulentOrderIDs[1]}");
Console.WriteLine($"Third: {fraudulentOrderIDs[2]}");

First: A123
Second: B456
Third: C789

步骤5-Reassign the value of the array

string[] fraudulentOrderIDs = new string[3];

fraudulentOrderIDs[0] = "A123";
fraudulentOrderIDs[1] = "B456";
fraudulentOrderIDs[2] = "C789";
// fraudulentOrderIDs[3] = "D000";

Console.WriteLine($"First: {fraudulentOrderIDs[0]}");
Console.WriteLine($"Second: {fraudulentOrderIDs[1]}");
Console.WriteLine($"Third: {fraudulentOrderIDs[2]}");

fraudulentOrderIDs[0] = "F000";

Console.WriteLine($"Reassign First: {fraudulentOrderIDs[0]}");

First: A123
Second: B456
Third: C789
Reassign First: F000

初始化数组

Just like when you declare a variable you can initialize it,You can use a special syntax with curly braces when declaring a new array,初始化新的数组.

步骤6-初始化数组

/*
string[] fraudulentOrderIDs = new string[3];

fraudulentOrderIDs[0] = "A123";
fraudulentOrderIDs[1] = "B456";
fraudulentOrderIDs[2] = "C789";
// fraudulentOrderIDs[3] = "D000";
*/

string[] fraudulentOrderIDs = { "A123", "B456", "C789" };

Console.WriteLine($"First: {fraudulentOrderIDs[0]}");
Console.WriteLine($"Second: {fraudulentOrderIDs[1]}");
Console.WriteLine($"Third: {fraudulentOrderIDs[2]}");

fraudulentOrderIDs[0] = "F000";

Console.WriteLine($"Reassign First: {fraudulentOrderIDs[0]}");

First: A123
Second: B456
Third: C789
Reassign First: F000

获取数组大小

要确定数组的大小,可使用 Length 属性.

步骤7-使用数组的Lengthproperty to print the number of the fake order

string[] fraudulentOrderIDs = { "A123", "B456", "C789" };

Console.WriteLine($"First: {fraudulentOrderIDs[0]}");
Console.WriteLine($"Second: {fraudulentOrderIDs[1]}");
Console.WriteLine($"Third: {fraudulentOrderIDs[2]}");

fraudulentOrderIDs[0] = "F000";

Console.WriteLine($"Reassign First: {fraudulentOrderIDs[0]}");

Console.WriteLine($"There are {fraudulentOrderIDs.Length} fraudulent orders to process.");

First: A123
Second: B456
Third: C789
Reassign First: F000
There are 3 fraudulent orders to process.

概括

使用数组时,The following important things should be kept in mind.

• 数组是一种特殊的变量,Used to hold a series of related data elements.
• The basic format of array variable declarations should be kept in mind.
• 访问数组的每个元素,Use the zero-based index inside square brackets to set or get its value.
• If trying to access an index outside the bounds of the array,则会出现运行时异常.
• Length property to programmatically determine the element number in an array.

练习-foreach语句

使用foreach遍历数组

foreach The statement iterates over each element in the array.

string[] names = { "Bob", "Conrad", "Grant" };
foreach (string name in names)
{
    Console.WriteLine(name);
}

在 foreach 关键字下,包含 Console.WriteLine(name); The code block will be names Executed once for each element of the array. 当 .Net When iterating over each element of the array at runtime,将存储在 names The value in the current element of the array is assigned to a temporary variable name,for easy access to code blocks.

Bob
Conrad
Grant

步骤1-创建并初始化int数组

int[] inventory = { 200, 450, 700, 175, 250 };

步骤2-添加foreachstatement to iterate through the array

int[] inventory = { 200, 450, 700, 175, 250 };

foreach (int items in inventory)
{

}

步骤3-Add a variable to sum the value of each element in the array

int[] inventory = { 200, 450, 700, 175, 250 };
int sum = 0;
foreach (int items in inventory)
{
    sum += items;
}

步骤4-Displays the final value of the sum 

int[] inventory = { 200, 450, 700, 175, 250 };
int sum = 0;
foreach (int items in inventory)
{
    sum += items;
}

Console.WriteLine($"We have {sum} items in inventory.");

We have 1775 items in inventory.

步骤5-创建一个变量,Used to store the current bucket number and display subtotals

int[] inventory = { 200, 450, 700, 175, 250 };
int sum = 0;
int bin = 0;
foreach (int items in inventory)
{
    sum += items;
    bin++;
    Console.WriteLine($"Bin {bin} = {items} items (Running total: {sum})");
}
Console.WriteLine($"We have {sum} items in inventory.");

Bin 1 = 200 items (Running total: 200)
Bin 2 = 450 items (Running total: 650)
Bin 3 = 700 items (Running total: 1350)
Bin 4 = 175 items (Running total: 1525)
Bin 5 = 250 items (Running total: 1775)
We have 1775 items in inventory.

概括

about this unit foreach Statements and other content,The following points need to be kept in mind.

• 使用 foreach statement to iterate through each element in the array,Executes the associated block of code once for each element in the array.
• foreach The statement sets the value of the current element in the array to a temporary variable,This temporary variable can be used in the body of the code block.
• 使用 ++ Increment operator will 1 to the current value of the variable.

挑战

To determine whether an element begins with a letter“B”开头,请使用 Stri

string[] orderIDs = { "B123", "C234", "A345", "C15", "B177", "G3003", "C235", "B179" };

foreach (string orderID in orderIDs)
{
    if (orderID.StartsWith("B"))
    {
        Console.WriteLine(orderID);
    }
}

ng.StartsWith() 方法. Check out the following simple example,了解如何使用 String.StartsWith() 方法,to use it in your code：

string name = "Bob";
if (name.StartsWith("B"))
{
    Console.WriteLine("The name starts with 'B'!");
}

The name starts with 'B'!

解决方案

string[] orderIDs = { "B123", "C234", "A345", "C15", "B177", "G3003", "C235", "B179" };

foreach (string orderID in orderIDs)
{
    if (orderID.StartsWith("B"))
    {
        Console.WriteLine(orderID);
    }
}

B123
B177
B179