String. Format method in C #

I. Definition
String. FormatIs to replace each format item in the specified String type data with the text equivalent item of the corresponding object value.
For example:

(1)
String p1 = "Jackie ";
String p2 = "Aillo ";
Response. Write (String. Format ("Hello {0}, I'm {1}", p1, p2 ));
(2)
Response. Write (String. Format ("Hello {0}, I'm {1}", "Jackie", "Aillo "));

The two have the same effect. Both Replace the values of the last two items with the {0} and {1} of the first item respectively }.
The output result is: Hello Jackie, I'm AilloIi. Multi-Format definition of String. Format:
The so-called multi-format refers to the definition of 1 ~ in a format item ~ Three format parameters. Each format parameter is separated by a semicolon. The value corresponding to the format items with two and three format parameters must be of the numerical type to determine whether it is negative, positive, or zero.
With 1 format parameter:

// Output in scientific notation format
Double p1 = 1000000;
Response. Write (String. Format ("{0: E2}", p1 ));

With two format parameters:

/* If the value corresponding to the format item is not negative, select the first format. If the value is negative, select the second format */
Double p1 = 10000;
Double p2 =-2420.50;
Response. Write (String. Format ("{0 :#,### 0.00 ;#,## 0.000 ;}< BR>", p1 ));
Response. Write (String. Format ("{0 :#,### 0.00 ;#,## 0.000 ;}", p2 ));

With three format parameters:

/* Select the first format when the value corresponding to the format item is positive;
The negative number is in the second format;
If the value is equal to zero, the third format */
1 double p1 = 10000;
Double p2 =-2420.50;
Double p3 = 0.00;
Response. write (String. format ("{0 :#,### 0.00 ;#,### 0.000 ;#,### 0.0000 }< BR>", p1 ));
Response. write (String. format ("{0 :#,### 0.00 ;#,### 0.000 ;#,### 0.0000 }< BR>", p3 ));
Response. Write (String. Format ("{0 :#,### 0.00 ;#,### 0.000 ;#,### 0.0000}", p2 ));

Supplement:
{0: N2}'N3, f3 'indicates the type of formatted data and the number of decimal places. For example, N2 indicates a number with two decimal places;
Similar to this:

N or n indicates a number.
F or f indicates a fixed point
E or e Indicates scientific notation
D or d indicates the decimal number.
X or x indicates hexadecimal
G or g indicates regular
C or c indicates currency