糖果火箭多少钱

書名： Corona SDK Mobile Game Development：Beginner's Guide（Second Edition）
作者名： Michelle M. Fernandez
本章字數： 523字
更新時間： 2021-07-23 19:37:19

Time for action – getting our hands full of strings

We're starting to familiarize ourselves with several blocks of code and how they interact with each other. Let's see what happens when we add in some expressions using strings and how different they are from just regular strings that you print out in the terminal:

Create a new project folder on your desktop and name it Working With Strings.
Make a new main.lua file in your text editor and save it to your folder.
Type out the following lines (do not include the line numbers in the code, they are only used for line reference):
```
1 print("This is a string!") -- This is a string!
2 print("15" + 1) -- Returns the value 16
```

Add in the following variables. Notice that it uses the same variable name:

3 myVar = 28
4 print(myVar)  -- Returns 28


5 myVar = "twenty-eight"
6 print(myVar) -- Returns twenty-eight

Let's add in more variables with some string values and compare them using different operators:

7 Name1, Phone = "John Doe", "123-456-7890"
8 Name2 = "John Doe"

9 print(Name1, Phone) -- John Doe  123-456-7890
10 print(Name1 == Phone) -- false
11 print(Name1 <= Phone) -- false
12 print(Name1 == Name2) -- true

Save your script and launch your project in Corona. Observe the results in the terminal window:
```
This is a string!
16
28
twenty-eight
John Doe 123-456-7890
false
false
true
```

What just happened?

You can see that line 1 is just a plain string with characters printed out. In line 2, notice that number 15 is inside the string and then added to the number 1, which is outside of the string. Lua provides automatic conversions between numbers and strings at runtime. Numeric operations applied to a string will try to convert the string to a number.

When working with variables, you can use the same one and have them contain a string and a number at different times, like in lines 3 and 5 (myVar = 28 and myVar = "twenty-eight").

In the last chunk of code (lines 7-12), we compared different variable names using relational operators. First, we printed the strings of Name1 and Phone. The next lines that follow compared Name1, Name2, and Phone. When two strings have the same characters in the exact order, then they are considered the same string and are equal to each other. When you look at print(Name1 == Phone) and print(Name1 <= Phone), the statement returns false because of the ASCII order. Digits are before alphabets, which are smaller when you compare them. In print(Name1 == Name2), both variables contain the same characters, and therefore, it returns true.

Have a go hero – pulling some more strings

Strings are pretty simple to work with since they are just sequences of characters. Try making your own expressions similar to the preceding example with the following modifications:

Create some variables with numerical values and another set of variables with numerical string values. Use relational operators to compare the values and then print out the results.
Use the concatenation operator, combine several strings or numbers together, and space them out equally. Print out the result in the terminal window.

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Corona SDK Mobile Game Development：Beginner's Guide（Second Edition）

Time for action – getting our hands full of strings

What just happened?

Have a go hero – pulling some more strings