Java beginners: a few simple small programs and new beginners, java small programs

Java beginners: a few simple small programs and new beginners, java small programs

Sort out several small programs written in the past few days, all of which are loop exercises.
// Set N to a four-digit number, which is 9 times the reverse order number.
// (For example, the inverse Number of 1234 is 4321), evaluate the N value
Package Azhi;
Public class Job_5 {
Public static void main (String [] args ){
For (int n = 1000; n <= 9999; n ++ ){
Int ge = n % 10;
Int shi = n % 100/10;
Int bai = n % 1000/100;
Int qian = n/1000;
Int temp = ge * 1000 + shi * 100 + bai * 10 + qian; // obtain the reverse order number.
If (temp = n * 9) {// It is 9 times its reverse order number.
System. out. println (n );
}
}
}
}

/* Print all "Daffodils ",
* The so-called "Daffodils" refers to a three-digit number, each of which is a numerical cube and equals to the number itself.
* For example, 153 is a "Daffodils" because 153 = the power of 1 + the power of 5 + the power of 3 */
Package Azhi;
Public class Job_6 {
Public static void main (String [] args ){
For (int I = 100; I <999; I ++ ){
Int g = I % 10;
Int s = I %100/10;
Int B = I/100;
Int temp = g * g + s * s + B * B; // each digit in three digits is equal to the number itself.
If (temp = I ){
System. out. print ("\ t" + I );
}
}
}
}

// Calculate the result of 1-2 + 3-4 + 5-... + 99-100
Package Azhi;
Public class Job_7 {
Public static void main (String [] args ){
Int sum = 0, sum1 = 0, sum2 = 0;
For (int I = 1; I <= 100; I ++ ){
If (I % 2 = 0) {// even number for Subtraction
Sum1-= I;
} Else {
Sum2 + = I; // Add an odd number
}
}
Sum = sum1 + sum2;
System. out. print (sum );
}
}

// Calculate the sum of the first 20 items of 2/1 + 3/2 + 5/3 + 8/5 + 13/8...
Package Azhi;
Public class Job_8 {
Public static void main (String [] args ){
Int I = 0;
Double x = 2.0, y = 1.0, z = 0.0;
Double sum = 0;
For (I = 1; I <= 20; I ++ ){
Sum = sum + x/y;
Z = x;
X = x + y;
Y = z;
}
System. out. print (sum );
}
}

// Output the 9*9 multiplication table
Package Azhi;
Public class Job_9 {
Public static void main (String [] args ){
For (int x = 1; x <= 9; x ++ ){
For (int y = 1; y <= x; y ++ ){
System. out. print ("\ t" + y + "×" + x + "=" + y * x );
}
System. out. println ();
}
}
}

/* Use the while LOOP
Calculate the multiples of 7 from 1 to and the sum of numbers with 7. 7 14 17 21 27 28 ...*/
Package Azhi;
Public class Seven100 {
Public static void main (String [] args ){
Int I = 0;
Int sum = 0;
While (I <= 1000 ){
Int ge = I % 10;
Int shi = I/10% 10;
Int bai = I/100;
If (I % 7 = 0 | ge = 7 | shi = 7 | bai = 7 ){
Sum + = I;
}
I ++;
}
System. out. println (sum );
}
}

These are simple small programs written over the past few days, but for beginners like me, these small programs are very good. First, I practiced the basic syntax, and then through these small programs, enhance your understanding of the program. I still have some problems writing these simple programs over the past few days. Take the question "2/1 + 3/2 + 5/3 + 8/5 + 13/8 ..... for the sum of the first 20 items, I haven't found the rule of this question for a long time. If I can't find the rule, I can't write the expression. Then I went to Baidu after thinking for a long time, then du Niang told me that it was very simple. I also found that it was very simple, but I didn't think of it at first. It may be more about my own exercises, but I don't know much about such questions and lack of consciousness.

Then, for the output of the 99 multiplication table, the inner loop I wrote is for (int y = 1; y <= 9; y ++). Now it is obvious that a rectangle is output, but I couldn't understand it at the time. To put it bluntly, I still couldn't understand it. The buddy next to me told me that I would write y <x because it loops in X.

Over the past few days, I have a general feeling that I need to work diligently to make it happen. For example, I used to calculate the number of days in a certain month in a certain year, mainly for the evaluation of a leap year. I wrote a lot about the whole program and it looked complicated and messy, but when I spoke about it, just a few simple words, and then I went back to what I just said. I practiced more and did more, and my experience was very important.