setprecision, fixed, Showpoint usage summary (classic!!) Super Classic!! ）

First you need to add a header file: Iomanip

One: setprecision

Function: Control the number of floating-point numbers displayed by the output stream, Setprecision (n) is the number of n output, there will be rounding.

For example: Double s=20.7843000,

Cout<<setprecision (1) <<s<<endl; will output 2e+001, because there is a number to output, so only 2.

Cout<<setprecision (2) <<s<<endl; will output 21.

Cout<<setprecision (3) <<s<<endl; will output 20.8.

Cout<<setprecision (6) <<s<<endl; will output 20.7843.

Cout<<setprecision (7) <<s<<endl; will output 20.7843.

Cout<<setprecision (8) <<s<<endl; will output 20.7843.

Visible, the fractional part of the end of 0 o'clock, can not be lost.

If you want to output, you have to use Showpoint.

Special tips:

(If you then add a two statement after these statements:

cout<<1<<endl;

cout<<1.00800<<endl;

Guess what it will output.

First output: 1. is not a floating-point type.

The second article is: 1.008. Take this rule statement for Setprecision (8).

Note:

If a statement is directly

int main ()

{

cout<<1<<endl;

cout<<1.00<<endl;

}

First output: 1.

The second article is also: 1. Output by integral type
）

II: Setprecision and Showpoint

Syntax: Declaring before the output statement: COUT.SETF (ios::showpoint); it's OK.

Also for example: Double s=20.7843000,

COUT.SETF (Ios::showpoint);

Cout<<setprecision (1) <<s<<endl; will output 2.e+001, note that 2 and e more than one "."

Cout<<setprecision (2) <<s<<endl; will output 21. Multiple points.

Cout<<setprecision (3) <<s<<endl; will output 20.8.

Cout<<setprecision (6) <<s<<endl; will output 20.7843.

Cout<<setprecision (7) <<s<<endl; will output 20.78430.

Cout<<setprecision (8) <<s<<endl; will output 20.784300.

Visible, the number of data you want is output.

Special tips:

(If you then add a two statement after these statements:

cout<<1<<endl;

cout<<1.0080<<endl;

Guess what it will output.

First output: 1. is not a floating-point type.

The second article is also: 1.0080000. Take this rule statement for Setprecision (8).

Three: Setprecision and fixed

If you want to keep a few decimal places, then Setprecision will have to work with fixed.

Syntax: Declaring before the output statement: COUT.SETF (ios::fixed);

For example: Double s=20.7843909

COUT.SETF (ios::fixed);

Cout<<setprecision (1) <<s<<endl; will output 2.8.

Cout<<setprecision (2) <<s<<endl; will output 21.78. Multiple points.

Cout<<setprecision (3) <<s<<endl; will output 20.784.

Cout<<setprecision (6) <<s<<endl; will output 20.784391.

Cout<<setprecision (7) <<s<<endl; will output 20.7843909.

Cout<<setprecision (8) <<s<<endl; will output 20.78439090.

Special tips:

(If you also add a two statement after these statements:

cout<<1<<endl;

cout<<1.008<<endl;

Guess what it will output.

First output: 1.

The second article is: 1.00800000.

is to take the setprecision (8) of this rule statement, is a floating-point type will retain 8 decimal places. is an integral type or an integral type. ）

Statements can also be written as: Cout<<fixed<<setprecision (2) <<s<<endl;

Even if the following statement does not write <<fixed, the same will be handled according to <<fixed.

For example, there are statements:

Cout<<fixed<<setprecision (2) <<s<<endl;

A:cout<<setprecision (7) <<s<<endl;

B:cout<<setprecision (8) <<s<<endl;

The AB statements are processed in 7, 8 decimal places, and no more than 7 or 8 floating-point numbers are processed.

If you have the following statement C:

Cout<<1.008<<endl; will also retain 8 decimal places.

Four: Setprecision, showpoint and fixed

{cout<<fixed<<setprecision (2) <<123.456<<endl;//output result is 123.46
cout<<showpoint<<12345.0006666<<endl;//Output 12345.0
Cout<<fixed<<setprecision (2) <<123.456<<endl;}

For example: Double s=20.7843909

1. There are statements

Cout<<setprecision (2) <<s<<endl;//output 21

cout<<fixed<<s<<endl;//Output 20.78

2. There are statements:

Cout<<setprecision (2) <<s<<endl;//output 21

cout<<showpoint<<s<<endl;//output 21. (one point)

3. There are statements:

cout<<fixed<<s<<endl;//Output 20.78391
cout<<showpoint<<s<<endl;//Output 20.78391
4. There are statements:

Cout<<setprecision (2) <<s<<endl;//output 21
cout<<fixed<<s<<endl;//Output 20.78
cout<<showpoint<<s<<endl;//Output 20.78

5. There are statements:

Cout<<setprecision (2) <<s<<endl;//output 21
Cout<<showpoint<<s<<endl;//21. (There's a point)
cout<<fixed<<s<<endl;//20.78