SOURCE

//3种循环

 var a = 0;
    for(var i = 1; i<=100 ; i++){
        a = a + i;
    }
document.write(a + "<br/>");


var i = 1; 
var b = 0;
while(i<=100){
    b=b+i;
    i++;
    }
document.write(b + "<br/>");


var i = 0; 
var c = 0;
do{ 
    i++;
    c=c+i;
}while(i<100)
document.write(c + "<br/>");