for循环

for循环的一种高效写法：


for死循环：

for(;;){}

练习1：计算0~100之间奇数和与偶数和

package big;
public class Annotation {
    public static void main(String[] args) {
        int oddSum = 0;
        int evenSum = 0;
        for (int i = 0; i < 100; i++) {
            if(i%2 == 0){
                evenSum += i;
            }
            else{
                oddSum += i;
            }
        }
        System.out.println("oddSum:"+oddSum);
        System.out.println("evenSum:"+evenSum);
    }
}

输出：

oddSum:2500
evenSum:2450

练习2：用while或for循环输出1~1000之间能被5整除的数，并且每行输出3个

其中for循环和while循环的方法稍不一样

package big;
public class Annotation {
    public static void main(String[] args) {
        int count = 0;
        int num = 1;
        for (int i = 1; i < 1000; i++) {
            if(i%5==0){
                count++;
                if(count == 3){
                    count = 0;
                    System.out.println(i);
                }
                else
                    System.out.print(i+"  ");
            }
        }
        System.out.println();
        System.out.println("**************************************************");
        while(num<1000){
            if(num % 5==0 && num % (5*3)==0){
                System.out.println(num);
            }
            else if(num % 5==0){
                System.out.print(num + "\t");
            }
            else{}
            num++;
        }
    }
}

练习3：打印99乘法表

package big;
public class Annotation {
    public static void main(String[] args) {
        int row=1;
        int col=1;
        while(row<=9){
            while(col<=row){
                if(col == row){
                    System.out.println(col+"*"+row+"="+row*col);
                }
                else
                    System.out.print(col+"*"+row+"="+row*col+"\t");
                col++;
            }
            row++;
            col=1;
        }
        //为了做出对称的三角哦~
        System.out.print("------------------------------------------------------------------------------");
        System.out.println();
        for(row-=1;row>=1;row--){
            for(;col<=row;col++){
                if(col == row) {
                    System.out.println(col + "*" + row + "=" + col * row);
                }
                else
                    System.out.print(col+"*"+row+"="+row*col+"\t");
            }
            col=1;
        }
    }
}