i=100时
for: i<101 true ==> print 100==> i++, i=101 ==> i<101 false; loop
while i<101 true ==> i++, i=101 ==> print 101 ==> i<101 false loop
for: i<101 true ==> print 100==> i++, i=101 ==> i<101 false; loop
while i<101 true ==> i++, i=101 ==> print 101 ==> i<101 false loop
其实你的while循环是从1开始计算的
i=0;
while(i<101){
j+=i;
i++;
}
while(i<101){
j+=i;
i++;
}