计算1+2+……+100的和

public class Sum{
public static void main(String[] args){
int a=100;//a用于设置最大数值
int sum=0;
int i;//用于循环
//先用while语句
i=a;
while (i>0){
sum=sum+i;
i=i-1;
}
System.out.println("the sum from 1 to " + a + " is :"+sum);
//用do while语句
i=a;
sum=0;
do{
sum=sum+i;
i=i-1;
}while(i>0);
System.out.println("the sum from 1 to " + a + " is :"+sum);
//用for 语句
sum=0;
for (i=1;i<=a;i=i+1){
sum=sum+i;
}
System.out.println("the sum from 1 to " + a + " is :"+sum);
}
}