Digit limitation from decimal point in C++

Question

I\'m new to C++. I have a double variable double a=0.1239857 and I want to limit variable a from decimal point two digits. So a will b

Answer 1

If you just want to output the value, you can do something like

printf("%.3f", a); // Output value with 3 digits after comma

If you want to convert the value itself, you can do:

a = (int)(a * 1000) / 1000.0f;

Note that both do no rounding, they just truncate the value.

Answer 2

you could also do something like this:

//This code will ask the user for an input, set the decimal precision to the hundredths place,  and add 4.63 to the inputted variable

int banana;
cin >> banana;
cout << setprecision(2) << fixed << banana + 4.63; 

Answer 3

Use a ios_base::precision for formatting i/o.

Answer 4

Are you actually trying to round the number, or just change its displayed precision?

For the former (truncating the extra digits):

double scale = 0.01;  // i.e. round to nearest one-hundreth
value = (int)(value / scale) * scale;

or (rounding up/down as appropriate, per jheriko's answer)

double scale = 0.01;  // i.e. round to nearest one-hundreth
value = floor(value / scale + 0.5) * scale;

For the latter:

cout << setprecision(2) << value;

where the parameter to setprecision() is the maximum number of digits to show after the decimal point.

Answer 5

An actual rounding solution would be x = floor(100*x + 0.5) / 100; assuming the value to be rounded is in a variable "x".

The x = floor(100*x) / 100; recommended by others here will actually truncate the number to 2dp instead.

Answer 6

This will result in two digits after the decimal place.

a = floor(a * 100.0) / 100.0;