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Javescript loop

2022-07-25 11:47:00 【c_ perfectworld】

loop

Purpose ： Repeat some statements

JS The cycle in

for loop
while loop
do...while loop

for loop

The statement that is repeatedly executed is called the loop body , Can we continue , Depends on the of the loop Termination conditions , A statement consisting of the body of a loop and its termination conditions , be called Loop statement

Grammatical structure ：

Initialize variable , Just use var A common variable declared , Usually used for timers

Conditional expressions are used to determine whether each cycle continues , Is the condition of termination

The operation expression is the code executed at the end of each loop , It is often used to update counter variables （ Increasing and decreasing ）

Execution process ：

Power off commissioning

double for loop

Print multiple lines and columns , It needs to be realized by loop nesting

A nested loop It refers to the structure of defining a circular statement in a circular statement , For example, in for In loop statement , You can nest another for loop , In this way for Circular statements we call double for loop

for Loop summary

for A loop can repeat some of the same code
for Loops can repeatedly execute different code , Because we have counters
for Loops can repeat certain operations , For example, arithmetic operators and addition operations
As demand increases , double for Can do more , Better to see
double for loop , Outer circle once , Inner layer for The loop is fully executed
for A cycle is a cycle in which cyclic conditions are directly related to numbers

while loop

while （ Conditional expression ） {
    // The loop body 
}

Execution ideas ： When the result of the conditional expression is true, be Execution loop body , otherwise Exit loop

do while loop

do {
    // The loop body 
} while （ Conditional expression ）

Execution ideas ： Follow while The difference is this do while First execute the loop body to judge the condition If the conditional expression turns out to be true , Then continue to execute the loop body , Otherwise exit the loop

do while Loop at least once

Be careful ： Execute the loop first , To determine , We will find that do...while The loop executes the loop code at least once

Loop summary

js There is for while do while There are three kinds of cycles
In many cases, the three cycles can be used instead of each other
If used for counting or numerical Correlation , The three are basically the same , But I prefer to use for
while and do while You can make more complex judgment conditions , Than for More flexible
while and do while The execution order is different ,while Judge before you execute ,do while Execute once before judgment
while and do while Execution times are different ,do while At least once ,while Maybe not once