What is this format specifier?

Submitted ⁨⁨1⁩ ⁨year⁩ ago⁩ by ⁨milon@lemm.ee⁩ to ⁨programming@programming.dev⁩

What is %.2f? Why is it not just %f? Is there some additional calculation happening? The half function already does all the calculations including splitting the bill, so I’m not sure what %.2f is. (Btw why is this code not formatting correctly in lemmy?)

`// Calculate your half of a restaurant bill

#include #include

float half(float bill, float tax, int tip);

int main(void) { float bill_amount = get_float("Bill before tax and tip: "); float tax_percent = get_float("Sale Tax Percent: "); int tip_percent = get_int("Tip percent: ");

printf("You will owe $%.2f each!\n", half(bill_amount, tax_percent, tip_percent));

}

// TODO: Complete the function float half(float bill, float tax, int tip) { bill += (bill * (tax / 100.0)); bill += (bill * (tip / 100.0));

bill /= 2;

return bill;

} `

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Comments

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steersman2484@sh.itjust.works ⁨1⁩ ⁨year⁩ ago
Please put your code between tripple backticks in a seperate line above an below your code. Single backticks are only for inline code like this.

To answer your question, the %.2f means it should only print two digits after the decimal point.

You can also use some other variations like this:

%2f print the number at least 2 characters wide

%5.2 print the number at leadt 5 characters wide with a precision of two digits after the decimal point

%05.2 the same as above, but fill leading digits with zeros

Just play a bit around with it and you will get it.
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ono@lemmy.ca ⁨1⁩ ⁨year⁩ ago
It’s a decimal floating point specifier with a precision sub-specifier.

cplusplus.com/reference/cstdio/printf/

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- joyjoy@lemm.ee ⁨1⁩ ⁨year⁩ ago
  Example with pi.
  
  #include #define PI 3.1415926 int main() { printf("%f.2", PI); // prints 3.14 return 0; }
  
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- Touching_Grass@lemmy.world ⁨1⁩ ⁨year⁩ ago
  This answer makes me so angry. Like you’re writing the answer to check if you know what it is instead of the person who asked
  
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  - ono@lemmy.ca ⁨1⁩ ⁨year⁩ ago
    
    This answer makes me so angry like revisiting trauma from learning programming.
    
    If you bothered to read the documentation, which exists in abundance on the web, in many books, and in the built-in manuals of various operating systems, and which I also linked in my answer, you would see a full explanation with clear examples.
    
    But you can’t be bothered with any of that, and instead expect other people to spend their time writing custom tutorials just for you?
    
    Your anger is misplaced. Please consider taking a walk.
    
    I just remember asking questions early on and getting answers more confusing that are even harder to parse
    
    When you ask people questions about their field of knowledge, and they don’t know you, it’s reasonable for them to assume you know the rudimentary basics. (Just as it would be reasonable for a fourth-year group to assume a that a stranger asking them questions has at least taken the first-year class.) Asking beyond your level of experience is not necessarily bad, but you should be ready to describe what you don’t understand, so that people can either elaborate with a helpful level of detail or send you to a forum more appropriate for your needs. For example:
    
    !learn_programming@programming.dev
    
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  - JackbyDev@programming.dev ⁨1⁩ ⁨year⁩ ago
    Which part of that is confusing to you? We can help make it easier to understand.
    
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Maoo@hexbear.net ⁨1⁩ ⁨year⁩ ago
%.2f% means it will format to two decimal places max. So 5.877 will format as 5.88 and 1 will format as 1.00.

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DirigibleProtein@aussie.zone ⁨1⁩ ⁨year⁩ ago
man printf

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- GuybrushThreepwo0d@programming.dev ⁨1⁩ ⁨year⁩ ago
  This is the way
  
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AlmightySnoo@lemmy.world ⁨1⁩ ⁨year⁩ ago
If you want multi-line code, you need to put it like this:

Image

For these kinds of questions, your best buddy is the documentation. In particular, a man ‘printf(3)’ yields:

Format of the format string

The format string is a character string, beginning and ending in its initial shift state, if any. The format string is composed of zero or more directives: ordinary characters (not %), which are copied unchanged to the output stream; and conversion specifications, each of which results in fetching zero or more subsequent arguments. Each conversion specification is introduced by the character %, and ends with a conversion specifier. In between there may be (in this order) zero or more flags, an optional minimum field width, an optional precision and an optional length modifier.

The overall syntax of a conversion specification is:

%[$][flags][width][.precision][length modifier]conversion

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- PoolloverNathan@programming.dev ⁨1⁩ ⁨year⁩ ago
  Wouldn’t man 3 printf do the same thing without the quotes?
  
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  - AlmightySnoo@lemmy.world ⁨1⁩ ⁨year⁩ ago
    Yup that definitely does the same thing.
    
    If anyone else is wondering why the 3 is there, it’s because usually you won’t find just one printf. You have the printf user command, the printf function from the standard C library, and POSIX manual entries for both the printf user command and C function. The id number is then an identifier for the corresponding section of the printf entry, and you can list all of them by doing a man -f printf.
    
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- starman@programming.dev ⁨1⁩ ⁨year⁩ ago
  Wait, you can use man on C++ functions?
  
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  - Eufalconimorph@discuss.tchncs.de ⁨1⁩ ⁨year⁩ ago
    On libc functions yes. Maybe on some from other libs, if they provide man pages.
    
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  - ono@lemmy.ca ⁨1⁩ ⁨year⁩ ago
    You can if you have those man pages installed.
    
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  - AlmightySnoo@lemmy.world ⁨1⁩ ⁨year⁩ ago
    Yup! Try also man malloc 😁
    
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  - JBloodthorn@kbin.social ⁨1⁩ ⁨year⁩ ago
    Back in my day, MS-DOS let you use HELP on QBASIC commands.
    
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qaz@lemmy.world ⁨1⁩ ⁨year⁩ ago
This formats the number with 2 decimals behind the dot.

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Bougie_Birdie@lemmy.blahaj.zone ⁨1⁩ ⁨year⁩ ago
%.2f will format your number rounded to two decimal places. So if you had 1 / 3 it would come out as 0.33 instead of 0.333333

% is the placeholder for the value .2 tells it ‘two spaces after the decimal’ f tells it that the placeholder is a float

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sharedburdens@hexbear.net ⁨1⁩ ⁨year⁩ ago
The .2f just means the float displays with only 2 significant figures ie cents.

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