Select structure

What is program structure

A program is a set of ordered instructions

Classification of program structure

Sequential structure / Selection structure / Loop structure

Selection structure

if Selection structure / switch Selection structure

basic if structure

every last if It will be carried out

if(result>60)

{

   alert(“ Congratulations , Pass the exam ”)

}

prompt Method   Input text box , You can also set the default value

!!! The type returned by the input box is the string type

There are two ways to convert strings into numbers :

1- Use the plus sign to convert the invisible data into numerical value

parseint You can convert strings into numbers

if…else structure

if( Conditions )

{

   //JavaScript sentence 1;

}

else

{

  //JavaScript sentence 2;

}

multiple if structure

As long as there is the right thing to do , Will not continue to implement

if ( Conditions 1 ) {

     // JavaScript sentence 1  

}

else  if ( Conditions 2 ) {

     // JavaScript sentence 2

}

else {

     // JavaScript sentence 3

}

Choice of structure switch sentence

stay switch The value of is equal to case The value of a constant is not only a comparison value , Also compare the types

switch ( expression )

{         

        case Constant 1 :

       javaScript sentence 1;

     break; ( Jump out of , Terminate the execution of the following statement , You must add )

     ......

  default :

              javaScript sentence n;

             break ;       ( Jump out of , Terminate the execution of the following statement , You must add )

}

Why use switch ？

Use multiple if structure ： Complicated structure , repetitive

Use switch structure ： Simple , clear

Loop structure

What is cycle

A cycle is when conditions are met , To perform an operation repeatedly

The characteristics of cyclic structure : Loop structure = The loop condition + Cyclic operation

for loop

for ( The initial part ; The loop condition ; Conditional iteration ) {

      // Statements executed in a loop

}

while Loop structure

// The initial part

while( The loop condition ) {

     // Cyclic operation

     // Iteration part

}

do-while loop

characteristic ： Execute first , To determine

do {

Cyclic operation

} while ( The loop condition );

for-in  loop

for( Variable in){ }

The advantages of recycling

Resolve duplicate actions

Reduce the amount of code written , Make the code structure clear

Improve the readability of the code