四舍五入到最近的10号

Question

I am trying to round an equation of two float numbers but it outputs without the decimals, it just rounds it to the nearest number for example 21.3 to 21. When I put ", 2" which should set it to round to the nearest 10th.

New code:

def add(op1,op2):
    result = int(round(op1 + op2, -1))
    print("")
    print ("Output: %d + %d = %d" % (op1, op2, result))

Output:

Output: 10 + 10 = 20

NEW

Output:

Output: 10.3 + 10.9 = 21.0

Code:

def add(op1,op2):
    result = int(round(op1 + op2, 1))
    print("")
    print ("Output: %0.1f + %0.1f = %0.1f" % (op1, op2, result))

Answer 1

Here's how to round a number to the nearest tenth:

>>> round(21.3331, 1)
21.3

Here's how to print out a floating point number with one decimal point:

>>> print "%.1f" % (21.3331,)
21.3

Note that if you do it using %d it will get printed as rounded to the nearest integer:

>>> print "%d" % (21.3331,)
21

See the String Formatting Operations docs for more on how the % formatting works.

Answer 2

Here's as simple one.

roundf(1.345 * 100) / 100

You simply multiply it by 100 before dividing it by 100 which preserves the value to 2 decimal places. This should be much more efficient than transforming it to a string and back.

Answer 3

You're converting to int . That means your result is an int . int s don't have fractional parts. Also, "%d" means format as int , so it will implicitly convert to int before printing. Use "%f" in your format string.

def add(op1,op2):
    result = round(op1 + op2, 1)
    print("")
    print ("Output: %0.1f + %0.1f = %0.1f" % (op1, op2, result))

Answer 4

There are two things here:

1. The numbers that are being calculated, do they have a fractional component? Are they integers (whole numbers), or floats (with a decimal point).

2. How do I display them?

Its important to distinguish between both:

1. Any operation on two integers will result in an integer; a number that does not have a decimal component. This is the internal type of the result.

2. If you do any calculation on two floats (numbers with a decimal point), the result will be a float.

3. If you an operation with an integer and a float, the result will be a float.

The round function changes the precision of the float (how many decimals are significant for you). So far we are not talking about how things are displayed or printed .

To print it with a decimal component, you need to format how its displayed , not change how its stored and used, this doesn't make a difference what the type of the number is. Here you can see I am printing an integer with a decimal component, even though it doesn't have one:

>>> i = 10 + 10
>>> i
20
>>> print("{0:.2f}".format(i))
20.00

And if you have a number with a decimal component; then depending on how you display it, various things will happen:

>>> i = 1.24556434532
>>> print("{0:.2f}".format(i))
1.25
>>> print("{0:.1f}".format(i))
1.2
>>> print("{0:.3f}".format(i))
1.246

So make sure you are doing the right thing at the right place.