This is a re-introduction. This time I wrote it for Python and in English, hence PE.

Once you have set up the programming environment, you can try to write a first small program.

The Goal

Today’s goal is a multiplication table (乘法表) as follows:

   1  2  3  4  5  6  7  8  9 10
   2  4  6  8 10 12 14 16 18 20
   3  6  9 12 15 18 21 24 27 30
   4  8 12 16 20 24 28 32 36 40
   5 10 15 20 25 30 35 40 45 50
   6 12 18 24 30 36 42 48 54 60
   7 14 21 28 35 42 49 56 63 70
   8 16 24 32 40 48 56 64 72 80
   9 18 27 36 45 54 63 72 81 90
  10 20 30 40 50 60 70 80 90 100

In words: The 10 rows (行) contain the multiples of the corresponding number. In every row the number, then its double (两次), then the triple (三次), …, the 10-fold (十次).

What Elements do we need?

1. A variable (变量/变数) can store a certain value, e.g.

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  x = 3

means that we create a variable named x and give it the value 3.

Correspondingly

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  name = "Mel"

is a variable named name (名字) that contains the text Mel (my name).

Of course, we do not want to type in the multiples manually, instead a computer should be able to compute it. We can reach that in the following way:

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  x*y

Assuming the variables x and y contain numbers, then x*y means that their product (求积) is computed. Correspondingly, we can compute a sum (求和) by 4+5.

2. What to do with these numbers?

We will print (印) them on the command line (命令行). The simplest option for that is:

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  print(x*y)

Everything between ( and ) will be printed by the print command. Print derives from printing on paper (纸上印刷), because the first computers did not have any montinor (or screen), but instead printed the results on paper (or displayed it with glowing electronic tubes).

3. We need one more ingredient

We want for every row 10 expressions and repeat that for 10 rows.

For one row this looks as follows

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2
3
4

  y = 5
  for x in range(1, 11):
      print(x*y, end=" ")
  print()

The first expression should be familiar y = 5 means that the variable y gets the value 5. for x in range(1, 11): means that the following indented command(s) will be reapeated for all numbers from 1 below 11. In the first iteration (迭代), we have x=1, in the second iteration x=2 and so on until x=10 (the last number below 11). This is called a for loop (for循环).

The refinement , end=" " means that we do not print each result on its own row, but followed by a space (空间, " “), all on the same row.

4. How do we form the whole table?

We should repeat the above block not only for y=5, but need to repeat it for y in 1..10 as follows:

1
2
3
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  for y in range(1, 11):
      for x in range(1, 11):
          print(x*y, end=" ")
      print()

How can I Start the Program?

If you set up your programming environment properly and wrote the programm in a new project, all you have to do is click the green arrow on the top bar and immediately the program will be executed.

Where can I see the result?

When you started the program as explained above, there will be a new sub window (窗) in which you can see the output (输出) of the program (that should look as the picture in the beginning). In this window you will maybe see even more output before, maybe you have to scroll (滚动) to the end.

5. How can I Improve the Program?

When you look at the output, you will see that all numbers in a row are printed one after the other with only one space. This means that the numbers in different rows are not aligned in columns (在列中对齐), because the earlier rows contain more 1-digit numbers. We can fix that by expanding every number to 2 digits (数字) as follows:

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  print("{:2}".format(x*y), end=" ")

.format(...) means that the following arguments (参数) will be inserted into the string before instead of the {...}. {:2} means that the numbers will be printed with 2 positions (or more) by padding them with spaces from the left if necessary.

What happens with 100? (It needs 3 digits.)

Have a look at the (new) output. Even though we requested only 2 digits, the number 100 is displayed with 3 digits. The reason is that {:2} means at least 2 positions, more when the number is bigger.

6. I want to print a bigger Multiplication table, like $20\times20$

Have a look at the line for y in range(1, 11):. 11 means that the last iteration runs with y=10. So what is the first change?

How do I make the Table square shaped (方形)?

We have 2 for loops for y in ...: and for x in ...:, i.e. you also have to adjust the 2nd for loop.

Another problem may be that from the middle of the table on, most numbers exceed the 2 digits. You can expand all numbers to 3 characters by adjusting to {:3}.format(...).

Please use the opportunity to try out different things…

Next time, we will talk about conditional commands and counting smurfs.