# [Learning] #16 JS: loop — Part 1

# while statement

If the statement is true, the code inside of {} would be executed.

When the first execution is done, the system will return to the while to repeat the execution.

The loop will stop until the result becomes false.

`var n=0;`

while(n<=50) {

n++;

}

alert(n);

var sum=0;

var i=1;

while(i<=100){

sum=sum+i; → it can be written as sum+=i as well.

i++;

}

alert(sum);

# for statement

- The concept of while and for is similar, but for combines 3 important blocks together, which makes the code simpler.
- Each of the statement means: for(
**initialization command**;**statement for decide whether the next loop continues;execute after every loop**){

}

`var sum=0;`

for(var i=1;i<=100;i++){

sum=sum+i;

}

alert(sum);

# break & continue

*break; → “jumps out” of a loop*(強制跳出迴圈)*continue; → “jumps over” one iteration in the loop*(強制進行下一次的迴圈)

by W3C Schools

**Example 1. while statement x break**

`var n=0`

while(n<=100){

if(n==50){

break;

}

n++;

}

alert(n);

=>n is 50.

**Example 2. for statement x continue**

`var x=0;`

for(var n=0;n<=100;n++){

if(n%4==0){ → n can be divided exactly by 4.

continue;

}

x++;

}

alert(x);

=>x is 75.