Keep valid digits; Keep n digits after the decimal point;

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Keep valid numbers

(1)setprecision(n)

 (2)%g

After decimal point n position

 (1)fixed

 （2）%f %lf

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Keep valid numbers

(1)setprecision(n)

• The header file  #include<iomanip>
• Specify the total number of display digits for a floating-point number , among n Is the number of digits required （ The sum of the digits before and after the decimal point .）, namely Retain n Significant digits ;
• rounding Make a reservation ;
• Not enough significant digits , Can't Make up automatically 0 （ If you want to make up 0 You can add showpoint namely cout<<setprecision(n)<<showpoint<<a; ）
• Until the accuracy changes , always Keep the effect
• If the number of digits before the decimal point More than Number of digits to be reserved , Use scientific counting

 

 (2)%g

• Keep valid numbers ; %.6g For the sake of reservation 6 Significant digits .
• If there is a suffix in the decimal part 0, be No output suffix 0;
• The default precision is 6;  %g Default hold 6 Significant digits

 

 

After decimal point n position

 (1)fixed

• You can force numbers to appear in the form of unscientific counting , By default , It can repair the decimal point 6 position ,
• fixed<<setprecision(n) The combination can be kept after the decimal point n position , Can be supplemented automatically 0

 （2）%f %lf

• %.2f float The type is reserved after the decimal point 2 position , %.2lf double The type is reserved after the decimal point 2 position
• Not enough digits , It can mend 0

Be careful ： Integer operation , If the last output result is decimal , To convert an integer to a floating point number