C process control statement

C# The process control statements are Judgment statement （ Conditional statements ）、 Loop statement 、 Loop control statement

One 、 Judgment statement （ Conditional statements ）

1. if....else sentence
2. switch....case sentence
3. Ternary operator

if Conditional statements

C# Support logical conditions in Mathematics ：

Less than （<）：x<y

Greater than （>）：x>y

be equal to （=）：x=y

Less than or equal to （<=）：x<=y

Greater than or equal to （>=）：x>=y

It's not equal to （!=）：x!=y

You can use these conditions to perform different actions on different decisions

C# Have the following conditional statements ：

If the specified condition is true, Then use if Specify the code block to execute

If the same condition is false, Then use else Specify the code block to execute

If the first condition is false, Then use else if Specify another condition to judge

Use switch Specify a number of optional code blocks to execute

1. if Conditional grammar

If the condition is true, Use if Statement specifies the C# Code block

grammar ：

if (condition)

{

    // If the condition is true, Then execute the code block

}

Example ：

In the following example , Judge two values 10 Is less than 20, If the condition is true, Then the console prints out “10 Less than 20” Text

if (10 < 20)

{

    Console.WriteLine("10 Less than 20");

}

You can also judge variables

int x = 15;

int y = 20;

if (x < y)

{

    Console.WriteLine("x<y");

}

2.else Sentence syntax

If the condition is false, Then use else Statement specifies the code block to execute

grammar ：

if (condition)

{

    // If the condition is true, Then execute the code block

}

else

{

    // If the condition is false, Then execute the code block

}

Example ：

In the following example , Judge num Is less than 15, If it is true, Then the console outputs “num Less than 15”; If it is false, Then the console outputs “num Greater than 15”. As a result, the console outputs “num Greater than 15”

int num = 20;

if(num < 15)

{

    Console.WriteLine("num Less than 15");

}

else

{

    Console.WriteLine("num Greater than 15");

}

// Output "num Greater than 15"

3.else if Sentence syntax

If the first condition is false, Then use else if Statement specifies the next condition

grammar ：

if (condition1)

{

    // If condition1 by true Execute code block

}

else if(condition2)

{

    // If condition1 by false,condition2 by true, Then execute code block level

}

else

{

    // condition and condition2 by false Execute code block

}

Example ：

int num = 20;

if (num < 15)

{

    Console.WriteLine("num Less than 15");

}

else if (num > 25)

{

    Console.WriteLine("num Greater than 25");

}

else

{

    Console.WriteLine("num be equal to 20");

}

// Output "num be equal to 20"

4. Nested if else sentence

if else Statements can be nested , That means you can be in another if perhaps else if Use in statement if perhaps else if sentence

grammar ：

if (condition1)

{ // If condition1 The value of the Boolean expression is true Execute code

    if (condition2)

    {

        // If condition2 The value of the Boolean expression is true Execute code

    }

}

Example ：

int x = 30;

int y = 10;

if (x == 30)

{

    if(y == 10)

    {

        Console.WriteLine("x = 30 and y = 10");

    }

    // Output "x = 30 and y = 10"

    if (y < 10)

    {

        Console.WriteLine("1");

    }else if (y < 20)

    {

        Console.WriteLine("2");

    }

    else

    {

        Console.WriteLine("3");

    }

    // Output "2"

}

5.if else Statement abbreviation （ Ternary operator ）

if else Conditional statements can also use a shortened form , It's called the ternary operator , Because it consists of three operands , It can be used to replace multiple lines of code with one line , It is usually used to replace simple if else sentence

grammar ：

variable = (condition) ? expressionTrue : expressionFalse;

Example ：

int num = 20;

if(num > 25)

{

    Console.WriteLine(" Good morning ");

}

else

{

    Console.WriteLine(" Good noon ");

}

Abbreviation ：

int num = 20;

string result = (num > 25) ? " Good morning " : " Good noon ";

Console.WriteLine(result);

6.switch

switch The expression in is a constant expression , Must be an integer or enumeration type , And the value cannot be the same

grammar ：

switch (expresstion)

{

    case a:

        // Code block

        break;

    case b:

        // Code block

        break;

    default:

        // Code block

}

switch case Sentences have the following rules ：

switch Statement expression Must be an integer or enumeration type , Or a class type , There is a single conversion function that converts it to an integer or enumeration type .

In a switch There can be any number of case sentence , Every case Followed by a value to compare and a colon ,case Of constant-expression Must be with switch Variables in have the same data type , And must be a constant , When the variable being tested equals case When the constant in ,case The following statement will be executed , Until I met break The statement so far , When you meet break When the sentence is ,switch End , The control flow will go to switch The next line after the statement .

Example ：

int num = 15;

switch (num)

{

    case 5:

        Console.WriteLine("5");

        break;

    case 15:

        Console.WriteLine("15");

        break;

    default:

        Console.WriteLine(" It doesn't work ");

        break;

}

// Output "num be equal to 15"

Two 、 Loop statement

As long as the specified conditions are met , Loop can execute code blocks

Circulation is convenient , Because they can save time , Reduce errors and make code more readable

There is while loop 、for loop

1. while loop

As long as the specified condition is true,while The loop will loop through a piece of code

Example ：

int num = 0;

while(num < 6)

{

    num++;

    Console.WriteLine(num);

}

Be careful ： We must change while Variables used in conditions , Otherwise the cycle will not end

2.do while Loop statement

do while Cycle is while A variant of the cycle . Check whether the condition is true Before , This loop will execute a block of code , Then as long as the condition is true, It will repeat the cycle

Example ：

int num = 0;

do

{

    num++;

    Console.WriteLine(num);

} while (num < 6);

3.for loop

When you know exactly how many times you want to traverse the code block , Use for Circulation is more convenient than while loop

grammar ：

for(statement1; statement2; statement3)

{

    // Block of code to execute

}

statement1 Execute before executing the code block （ once ）

statement2 Defines the conditions for executing code blocks

After executing the code block （ Every time ） It will be carried out statement3

Example ：

for (int i = 0; i < 10; i++)

{

    Console.WriteLine(i);

}

4.foreach loop

grammar ：

foreach(type variableName:arrayName){

    // Block of code to execute

}

Example ：

string[] arr = { " Apple "," grapes "," blueberries "," watermelon "};

foreach(var item in arr)

{

    Console.WriteLine(item);

}

3、 ... and 、 Loop control statement

1.break keyword

break The function of is to jump out of the current circular code block （for、while、do while） or switch Code block . The function in the loop code block is to jump out of the current loop body . stay switch The function in the code block is to interrupt and next case Comparison of conditions

Example ：

In the following example, when i be equal to 5 when , Out of the loop

for(int i = 0; i < 10; i++)

{

    if(i == 5)

    {

        break;

    }

    Console.WriteLine(i);

}

2.continue keyword

continue Used to end the execution of subsequent statements in the loop body , And jump back to the beginning of the loop block to execute the loop

Example ：

In the following example, when i be equal to 5 when , Skip this cycle

for(int i = 0; i < 10; i++)

{

    if(i == 5)

    {

        continue;

    }

    Console.WriteLine(i);

}