publicclass control {
publicstaticintsum(int n){
int count=0;for(int i=0;i<=n;i++){
if(i%10==9){
count++;}if(i/10==9){
count++;}}return count;}publicstaticvoidmain(String[] args){
int n=100;int s=sum(n);System.out.println("9的个数为"+s);}}
2.输出 1000 - 2000 之间所有的闰年
publicclass means {
publicstaticvoidmain(String[] args){
int s=0;int i=0;for(i=1000;i<2000;i++){
if((i%4==0&&i%100!=0)||(i%400==0)){
System.out.println(i);}}}}
3.打印 1 - 100 之间所有的素数
publicclass control {
publicstaticvoidmain(String[] args){
int i=0;for(i=2;i<100;i++){
boolean s=fun(i);if(s==true){
System.out.println(i);}}}publicstaticbooleanfun(int n){
for(int i=2;i<n/2;i++){
if(n%i==0){
returnfalse;}}returntrue;}}