编写循环小案例

打印等腰三角形

• 第1次推导

public class test {
    public static void main(String[] args) {
        // 行数
        int a = 3;

        System.out.println();
        System.out.print(" ");
        System.out.print(" ");
        System.out.print("*");

        System.out.println();
        System.out.print(" ");
        System.out.print("*");
        System.out.print("*");
        System.out.print("*");

        System.out.println();
        System.out.print("*");
        System.out.print("*");
        System.out.print("*");
        System.out.print("*");
        System.out.print("*");

    }
}

• 第2次推导

public class test {
    public static void main(String[] args) {
        // 行数
        int a = 3;

        System.out.println();
        for (int i=1; i<=2; i++){
            System.out.print(" ");
        }
        for (int i=1; i<=1; i++){
            System.out.print("*");
        }

        System.out.println();
        for (int i=1; i<=1; i++){
            System.out.print(" ");
        }
        for (int i=1; i<=3; i++){
            System.out.print("*");
        }

        System.out.println();
        for (int i=1; i<=0; i++){
            System.out.print(" ");
        }
        for (int i=1; i<=5; i++){
            System.out.print("*");
        }

    }
}

• 最后完善

public class test {
    public static void main(String[] args) {
        // 行数
        int a=5;

        int b=1;
        for (int j=a; j>=1; j--){
            System.out.println();
            for (int i=1; i<j; i++){
                System.out.print(" ");
            }
            for (int i=1; i<=b; i++){
                System.out.print("*");
            }
            b+=2;
        }

    }
}

打印九九乘法表

• 第1次推导

public class test {
    public static void main(String[] args) {
        System.out.println();
        System.out.print(1 + "*" + 1 + "=" + 1*1);
        System.out.print(",");

        System.out.println();
        System.out.print(1 + "*" + 2 + "=" + 1*2);
        System.out.print(",");
        System.out.print(2 + "*" + 2 + "=" + 2*2);
        System.out.print(",");

        System.out.println();
        System.out.print(1 + "*" + 3 + "=" + 1*2);
        System.out.print(",");
        System.out.print(2 + "*" + 3 + "=" + 2*3);
        System.out.print(",");
        System.out.print(3 + "*" + 3 + "=" + 3*3);
        System.out.print(",");

    }
}

• 第2次推导

public class test {
    public static void main(String[] args) {
        int j=0;

        j++;
        System.out.println();
        for (int i=1; i<=j; i++){
            System.out.print(i + "*" + j + "=" + i*j);
            System.out.print(",");
        }

        j++;
        System.out.println();
        for (int i=1; i<=j; i++){
            System.out.print(i + "*" + j + "=" + i*j);
            System.out.print(",");
        }

        j++;
        System.out.println();
        for (int i=1; i<=j; i++){
            System.out.print(i + "*" + j + "=" + i*j);
            System.out.print(",");
        }

    }
}

• 最终完善

public class test {
    public static void main(String[] args) {
        int j=0;
        for (int n=1; n<=9; n++){
            j++;
            System.out.println();
            for (int i=1; i<=j; i++){
                System.out.print(i + "*" + j + "=" + i*j);
                System.out.print(",");
            }
        }

    }
}

求和

• 给定一个整数，求出每个位数的和，例如：1234，结果：1+2+3+4=10
• 第1次推导

public class test {
    public static void main(String[] args) {

        int a=12;
        int b=a/10;
        int c=a%10;
        System.out.println(b + "," + c);

        int a=123;
        int b=a/100;
        int c=a/10;
        int c1=c%10;
        int d=a%10;
        System.out.println(b + "," + c + "," + c1 + "," + d);

        int a=1234;
        int b=a/1000;
        int c=a/100;
        int c1=c%10;
        int d=a/10;
        int d1=d%10;
        int e=a%10;
        System.out.println(b + "," + c + "," + c1 + "," + d + "," + d1 + "," + e);

    }
}

• 完善步骤

public class test {
    public static void main(String[] args) {
        int a=12345;
        int sum=0;
        int n=get0(a);
        // 第1位
        int m = get1(n);
        int f=a/m;
        System.out.println(f);
        sum+=f;
        // 中间
        for(int j=n-1; j>1; j--){
            int p=a/get1(j);
            int p1=p%10;
            System.out.println(p1);
            sum+=p1;
        }
        // 最后1位
        int e=a%10;
        System.out.println(e);
        sum+=e;
        System.out.println(sum);
    }

    // 位数
    public static int get0(int a){
        int b;
        int i=1;
        do{
            b = a/10;
            a = b;
            System.out.println(b);
            i++;
        }while (a>10);
        System.out.println("b小于10" + "," + i);
        return i;
    }

    // 要除的商
    public static int get1(int n){
        int m=1;
        for(int i=1; i<n; i++){
            m*=10;
        }
        System.out.println(m);
        return m;
    }

}

• 最终完善

public class test {
    public static void main(String[] args) {
        int a = 12365;
        int sum=0;
        do{
            sum+=a%10;
            a=a/10;
        }while (a>0);
        System.out.println(sum);

    }
}