方法调用小练习

1. 写⼀个函数add，接收两个整数作为参数，返回这两个整数的和

public class TestSum {
	public static void main(String[] args) {
		
		int sum = add(1,2);
		System.out.println(sum);
		
	}
	
	public static int add(int num1,int num2) {
		
		return num1 + num2;
		
	}
}

2. 写⼀个函数，接收⼀个整数，输出这个整数的所有因⼦

public class TestReceive {
    public static void main(String[] args) {
        
        number(51);
        
    }
    
	public static int number(int num) {
		
		if(num == 0) {
			
			return 0;
			
		} else {
			
			System.out.println(1);
			
			for(int i = 2; i <= num; i++) {
				if(num % i == 0) {
					
					System.out.println(i);
					
				}
			}

        }
		return 1;
	}
}

3. 写⼀个函数，接收⼀个整数n，输出1+2+3+…+n 的和

//写一个函数，接收一个整数n，输出1+2+3+...+n 的和

import java.util.Scanner;

public class TestSum {
    public static void main(String[] args) {
		
		int num = number();

		int result = numberSum(num);
	
		System.out.println(result);
	
	}
	public static int number() {
		
		Scanner input = new Scanner(System.in);
		System.out.println("请输入一个整数：");
         
		return input.nextInt();

		
	}
    
    public static int numberSum(int num) {
		 
        if(num == 1) {
            return 1;
        } else {
            
            return num + numberSum(num - 1);
            
        }
        
    } 
}

4. 写⼀个函数，接收⼀个整数参数n，输出n 个HelloWorld

import java.util.Scanner;

public class Test1 {
    public static void main(String[] args) {
		
	int num = number();	
	numberSum(num);
	
	}
	public static int number() {
		
		Scanner input = new Scanner(System.in);
		System.out.println("请输入一个整数n：");
         
		return input.nextInt();

		
	}
    
    public static int numberSum(int n) {
		 
		for(int i = 1;i <= n; i++) {
			
				System.out.println("HelloWorld");
			
			}
			return 1;
        }
	} 

5. 写⼀个函数，接收⼀个整数，输出这个整数是⼏位数

import java.util.Scanner;

public class Test2 {
    public static void main(String[] args) {
		
	int num = number1();	
	number2(num);
	
	}
	public static int number1() {
		
		Scanner input = new Scanner(System.in);
		System.out.println("请输入一个整数n：");
         
		return input.nextInt();

		
	}
    
    public static int number2(int n) {
		
			int count = 1;
			while(n >= 10) {
				
				count++;
				n /= 10;
				
			}
		
			System.out.println(count);
			return 1;
        }
	} 

6. 求⼀个三位数，该三位数等与其每位数字的阶乘之和

public class TestSum1 {
	public static void main(String[] args) {
		
		int a, b, c, i;//for循环找那个满足条件的三位数（i）
		for (i = 100 ; i <= 999; i++) {
			a = i % 10;			//个位
			b = i / 10 % 10;	//十位
			c = i / 100;		//百位
			if (i == factorial(a) + factorial(b) + factorial(c)) {
				System.out.println("其三位数是：" + i);
			}
		}
	}
	//求阶乘
	public static int factorial(int num) {
		int sum = 1;
		for (int i = 1; i <= num; i++) {
			sum *= i;
		}
		return sum;
	}
}

7. 验证哥德巴赫猜想：任何⼀个⼤于6的偶数，都能分解成两个质数的和。要求输⼊⼀个整数，输出这个数能被分解成哪两个质数的和

import java.util.Scanner;

public class Test4 {
    public static void main(String[] args) {
	
     	Scanner sc = new Scanner(System.in);
		
        System.out.println("请输入一个整数：");
		
        int n = sc.nextInt();
		
       for(int i = 1; i <= n/2; i++) {
		   
           int j = n - i;
		   
           if(primeNumbers(i) && primeNumbers(j)) {
			   
               System.out.println(n + " = " + i + " + " + j);
			   
          }
       }
	}
	public static boolean primeNumbers(int n) {
		
		boolean falg = true;//初始化falg为true
        
        if(n < 3) {//2,3为最小的质数
		
            falg = n > 1;
			
        }
        for(int i = 2; i <= Math.sqrt(n); i++) {//Math.sqrt(n) 为n的开方，如16的开方为4
            if(n % i == 0) {
				
                falg = false;
				
            }
        }
		
        return falg;  
	}
}