Ask the VFP master for help, and the VFP asks for help

There is no guarantee that the full vertical manuscript is correct, and you Yu Ji Jing infiltrated it to verify it.

1.“scan ..The endscan command is a command block between "scan" and "endscan" for each record in the current table that moves the record pointer sequentially and executes it for each record that meets the specified criteria.

If you don't open the table, you can't move the record pointer in the table and execute commands on the record. The answer B is correct, but the question itself is not rigorous, because: in VF, database and table are two different concepts, and a table can be a "database table" that belongs to a certain database, or a "free table" that does not belong to any database; Execute "scan.."

endscan" must open a "table", not a "database", for example, no database is established at all, and "scan" can be executed only for a free table that is currently openendscan”。This topic confuses the VF's "database" with "table" and should be changed to "a table must be opened".

The example in the book is not opened" may have omitted the use command, but there must have been a qualification such as "current table" when interpreting the command. In summary, you can only perform "scan.." on tables that are open in the current workspaceendscan”

2."& is a command to execute macro substitution, which uses the contents of memory variables and array elements as original strings, and the variables immediately following it can indeed only be character-based, but the variable can be used as various data types supported by VF according to the writing format when assigning values to the variable when performing macro substitution. For example:

Execute a known x="134", &x is 134 and &x+478 is 134+478, and the result is exactly the same (in this case, although x itself is a character variable, its value is"134", but when &x+478 is executed, &x is replaced with a value of 134, i.e., 134+478 is actually executed, resulting in 612;If written as x="'134'"or x='"134"', in the case of &x +478, the string is used"134"Replace &x, i.e., what is actually executed"134"+478, a "operand type mismatch" error will occur and no result will be obtained; To get"134478"As a result, the two statements should be executed first with x="'134'", and then go to &x +"478"）

The data type of x assignment format &x is an equivalent representation of &x.

x="134"Numeric type 134

x="'134'"Character type'134'

x=""Date type.

x=".t."Logicalt.……

1 It should be precise that a data table must be opened and scan is applied to the current table.

2 &x is to replace the expression with the content of the string double quotes, note that the content in the x double quotation marks is the value 134, so &x + 478 is replaced with 134 + 478, so that the value of the expression is 612.

The first question, the estimated answer is wrong, I think the answer should be A, about the B answer, using the scan loop structure, you must open the table file, not the database.

Question 2. "134"It is a character type instead of a numeric type, and 134 is a numeric type, and the delimiter (single quotes, double quotation marks, or square brackets) must be used when using character data

You need to know that there are many tables under the database, and if you want to find a model, you must first know which table the "model" field is in the database, and then you can use the command to find the "model" field in the specific table.

For example, the name of the database is "Invoicing", and there is a table called "Product Catalog Table", and there is a field called "Model".

To find an item with the model number "ACER 4736", you can run the following two commands:

1. The following command is to find the model as ="acer 4736"products, to find exactly, the characters must be exactly the same.

use product catalog table.

locate for model ="acer 4736"

2. The following command searches for products that contain "acer" in the model number, as long as the model number contains this character.

use product catalog table.

locate for "acer"$ model.

Note: The "$" in VFP stands for "contained in", which is equivalent to the usage of the at() function. (similar to the like usage in other programming languages).

1, at first A is 10 and B is 20

2, and then call the procedure sub, pass a and b in.

A is passed to x by reference, and when the value of x is changed, a also changes.

b is passed to y by value, and y has nothing to do with b.

3,sub changes x to the square of x, so a=1004, and the result is 100 20