Mfcttrf

Why is matter-antimatter asymmetry surprising, if asymmetry can be generated by a random walk in which particles go into black holes?

Transiting through Switzerland by coach with lots of cash

Can I use I2C over 2m cables?

Find the percentage

Solving a Certainty Equivalent (Decision Analysis) problem

Creating chess engine, machine learning vs. traditional engine?

How to ride a fish?

How acceptable is an ellipsis "..." in formal mathematics?

Low-magic medieval fantasy clothes that allow the wearer to grow?

What is the next number in the series: 21, 21, 23, 20, 5, 25, 31, 24,?

Can I color text by using an image, so that the color isn't flat?

How to copy the path of current directory in ubuntu 18.04

Does "Op. cit." stand for "opus citatum" or "opere citato"?

Tikz – Box/frame arround Text with interruption

There is any way today to recover/dump 2M disks?

Noun phrase and is

What is the meaning of "log" in this sentence?

how do you value what your leisure time is worth?

In Men at Arms, why announce Edward was caught?

My first random password generator

Proving roots of a function cannot all be real

grep pairs of patterns and file

How to find out which object is taking space?

What can I do to avoid potential charges for bribery?

Why does %f print large values when floating point constants are passed instead of variables?

Is floating point math broken?Correct format specifier for double in printf'float' vs. 'double' precisionWhy does printf() promote a float to a double?How does printf and co differentiate between float and doubleC read file line by lineWhat happens to a float variable when %d is used in a printf?Hexadecimal Floating-Point ConstantWhy are elementwise additions much faster in separate loops than in a combined loop?How dangerous is it to compare floating point values?Why does the C preprocessor interpret the word “linux” as the constant “1”?Why does GCC generate 15-20% faster code if I optimize for size instead of speed?Why the same variable print the different output?Why are the int and float passed in printf going to the wrong positions in the format string?Float and int members in a union does not show values

.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty
margin-bottom:0;

8

1

In the given program why did I get different results for each of the printfs?

#include <stdio.h>
int main()

 float c = 4.4e10;
 printf("%fn", c);
 printf("%fn", 4.4e10);
 return 0;

And it shows the following output:

44000002048.000000
44000000000.000000

c

share|improve this question

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

asked 8 hours ago

user10056563user10056563

4433 bronze badges

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  The answers so far explain that 4.4e10 is a double constant which is converted to float in the initialization of c but kept as a double when passed to printf. However, you might also like to know that adding an f suffix makes it a float constant: Printing 4.4e10f will show the same value that results from initializing c to 4.4e10f. Distinguishing float constants from double constants can be important to doing quality work with floating-point arithmetic.
  
  – Eric Postpischil
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is this conversion method named anything? I want to read about it.
  
  – user10056563
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Do you want to know when the conversion from double to float occurs in the C language? Or do you want to know what values result from the conversion, that is, what effects the conversion has? Or something else?
  
  – Eric Postpischil
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I'm questioning neither the replies here nor the standard but, when I was young and learning C we used printf("%f",x) for a float and printf("%lf",x) for a double. When did things change? And how would one explicitly printf a (single) float - printf("%hf",x)??
  
  – Adrian
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @Adrian %lf in printf is the same thing as %f. A float in a variable argument is converted into a double by the compiler, just like a short gets converted into an int.
  
  – JL2210
  7 hours ago
  
  

  
  
  
  

 | 
show 3 more comments

8

1

In the given program why did I get different results for each of the printfs?

#include <stdio.h>
int main()

 float c = 4.4e10;
 printf("%fn", c);
 printf("%fn", 4.4e10);
 return 0;

And it shows the following output:

44000002048.000000
44000000000.000000

c

share|improve this question

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

asked 8 hours ago

user10056563user10056563

4433 bronze badges

• 
  
  
  

  
  4
  

  
  
  
  
  
  

  
  
  The answers so far explain that 4.4e10 is a double constant which is converted to float in the initialization of c but kept as a double when passed to printf. However, you might also like to know that adding an f suffix makes it a float constant: Printing 4.4e10f will show the same value that results from initializing c to 4.4e10f. Distinguishing float constants from double constants can be important to doing quality work with floating-point arithmetic.
  
  – Eric Postpischil
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Is this conversion method named anything? I want to read about it.
  
  – user10056563
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Do you want to know when the conversion from double to float occurs in the C language? Or do you want to know what values result from the conversion, that is, what effects the conversion has? Or something else?
  
  – Eric Postpischil
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  I'm questioning neither the replies here nor the standard but, when I was young and learning C we used printf("%f",x) for a float and printf("%lf",x) for a double. When did things change? And how would one explicitly printf a (single) float - printf("%hf",x)??
  
  – Adrian
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  2
  

  
  
  
  
  
  

  
  
  @Adrian %lf in printf is the same thing as %f. A float in a variable argument is converted into a double by the compiler, just like a short gets converted into an int.
  
  – JL2210
  7 hours ago
  
  

  
  
  
  

 | 
show 3 more comments

In the given program why did I get different results for each of the printfs?

#include <stdio.h>
int main()

 float c = 4.4e10;
 printf("%fn", c);
 printf("%fn", 4.4e10);
 return 0;

And it shows the following output:

44000002048.000000
44000000000.000000

c

share|improve this question

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

asked 8 hours ago

user10056563user10056563

4433 bronze badges

#include <stdio.h>
int main()

 float c = 4.4e10;
 printf("%fn", c);
 printf("%fn", 4.4e10);
 return 0;

44000002048.000000
44000000000.000000

share|improve this question

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

asked 8 hours ago

user10056563user10056563

4433 bronze badges

share|improve this question

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

asked 8 hours ago

user10056563user10056563

4433 bronze badges

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

asked 8 hours ago

user10056563user10056563

4433 bronze badges

asked 8 hours ago

user10056563user10056563

4433 bronze badges

2 Answers
2

active

oldest

votes

8

A float is a type that holds a 32-bit floating point number, while the constant 4.4e10 represents a double, which holds a 64-bit floating point number (i.e. a double-precision floating point number)

When you assign 4.4e10 to c, the value 4.4e10 cannot be represented precisely (a rounding error in a parameter called the mantissa), and the closest possible value (44000002048) is stored. When it is passed to printf, it is promoted back to double, including the rounding error.

In the second case, the value is a double the whole time, without narrowing and widening, and it happens to be the case that a double can represent the value exactly.

If this is undesirable behavior, you can declare c as a double for a bit more precision (but beware that you'll still hit precision limits eventually).

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

ζ--ζ--

31.5k44 gold badges6666 silver badges9191 bronze badges

add a comment
 | 

3

You're actually printing the values of two different types here.

In the first case you're assigning a value to a variable of type float. The precision of a float is roughly 6 or 7 decimal digits, so unless the value can be represented exactly you'll see the closest value that can be represented by that type.

In the second case you're passing the constant 4.4e10 which has type double. This type has around 16 decimal digits of precision, and the value is within that range, so the exact value is printed.

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

dbushdbush

114k1515 gold badges129129 silver badges162162 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why it specifically prints 2048 at the end ?
  
  – user10056563
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @user10056563 Because that's the closest number to 4.4e10 that can be stored in a 32 bit float.
  
  – dbush
  8 hours ago
  

  
  
  
  

add a comment
 | 

Your Answer

StackExchange.ifUsing("editor", function ()
StackExchange.using("externalEditor", function ()
StackExchange.using("snippets", function ()
StackExchange.snippets.init();
);
);
, "code-snippets");

StackExchange.ready(function()
var channelOptions =
tags: "".split(" "),
id: "1"
;
initTagRenderer("".split(" "), "".split(" "), channelOptions);

StackExchange.using("externalEditor", function()
// Have to fire editor after snippets, if snippets enabled
if (StackExchange.settings.snippets.snippetsEnabled)
StackExchange.using("snippets", function()
createEditor();
);

else
createEditor();

);

function createEditor()
StackExchange.prepareEditor(
heartbeatType: 'answer',
autoActivateHeartbeat: false,
convertImagesToLinks: true,
noModals: true,
showLowRepImageUploadWarning: true,
reputationToPostImages: 10,
bindNavPrevention: true,
postfix: "",
imageUploader:
brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/4.0/"u003ecc by-sa 4.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
allowUrls: true
,
onDemand: true,
discardSelector: ".discard-answer"
,immediatelyShowMarkdownHelp:true
);



);

draft saved

draft discarded

Sign up or log in

StackExchange.ready(function ()
StackExchange.helpers.onClickDraftSave('#login-link');
);

Sign up using Google

Sign up using Facebook

Sign up using Email and Password

Post as a guest

Name

Email

Required, but never shown

StackExchange.ready(
function ()
StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fstackoverflow.com%2fquestions%2f58187573%2fwhy-does-f-print-large-values-when-floating-point-constants-are-passed-instead%23new-answer', 'question_page');

);

Post as a guest

Name

Email

Required, but never shown

8

A float is a type that holds a 32-bit floating point number, while the constant 4.4e10 represents a double, which holds a 64-bit floating point number (i.e. a double-precision floating point number)

When you assign 4.4e10 to c, the value 4.4e10 cannot be represented precisely (a rounding error in a parameter called the mantissa), and the closest possible value (44000002048) is stored. When it is passed to printf, it is promoted back to double, including the rounding error.

In the second case, the value is a double the whole time, without narrowing and widening, and it happens to be the case that a double can represent the value exactly.

If this is undesirable behavior, you can declare c as a double for a bit more precision (but beware that you'll still hit precision limits eventually).

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

ζ--ζ--

31.5k44 gold badges6666 silver badges9191 bronze badges

add a comment
 | 

8

A float is a type that holds a 32-bit floating point number, while the constant 4.4e10 represents a double, which holds a 64-bit floating point number (i.e. a double-precision floating point number)

When you assign 4.4e10 to c, the value 4.4e10 cannot be represented precisely (a rounding error in a parameter called the mantissa), and the closest possible value (44000002048) is stored. When it is passed to printf, it is promoted back to double, including the rounding error.

In the second case, the value is a double the whole time, without narrowing and widening, and it happens to be the case that a double can represent the value exactly.

If this is undesirable behavior, you can declare c as a double for a bit more precision (but beware that you'll still hit precision limits eventually).

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

ζ--ζ--

31.5k44 gold badges6666 silver badges9191 bronze badges

add a comment
 | 

A float is a type that holds a 32-bit floating point number, while the constant 4.4e10 represents a double, which holds a 64-bit floating point number (i.e. a double-precision floating point number)

When you assign 4.4e10 to c, the value 4.4e10 cannot be represented precisely (a rounding error in a parameter called the mantissa), and the closest possible value (44000002048) is stored. When it is passed to printf, it is promoted back to double, including the rounding error.

In the second case, the value is a double the whole time, without narrowing and widening, and it happens to be the case that a double can represent the value exactly.

If this is undesirable behavior, you can declare c as a double for a bit more precision (but beware that you'll still hit precision limits eventually).

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

ζ--ζ--

31.5k44 gold badges6666 silver badges9191 bronze badges

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

ζ--ζ--

31.5k44 gold badges6666 silver badges9191 bronze badges

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

ζ--ζ--

31.5k44 gold badges6666 silver badges9191 bronze badges

answered 8 hours ago

ζ--ζ--

31.5k44 gold badges6666 silver badges9191 bronze badges

3

You're actually printing the values of two different types here.

In the first case you're assigning a value to a variable of type float. The precision of a float is roughly 6 or 7 decimal digits, so unless the value can be represented exactly you'll see the closest value that can be represented by that type.

In the second case you're passing the constant 4.4e10 which has type double. This type has around 16 decimal digits of precision, and the value is within that range, so the exact value is printed.

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

dbushdbush

114k1515 gold badges129129 silver badges162162 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why it specifically prints 2048 at the end ?
  
  – user10056563
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @user10056563 Because that's the closest number to 4.4e10 that can be stored in a 32 bit float.
  
  – dbush
  8 hours ago
  

  
  
  
  

add a comment
 | 

3

You're actually printing the values of two different types here.

In the first case you're assigning a value to a variable of type float. The precision of a float is roughly 6 or 7 decimal digits, so unless the value can be represented exactly you'll see the closest value that can be represented by that type.

In the second case you're passing the constant 4.4e10 which has type double. This type has around 16 decimal digits of precision, and the value is within that range, so the exact value is printed.

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

dbushdbush

114k1515 gold badges129129 silver badges162162 bronze badges

• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  Why it specifically prints 2048 at the end ?
  
  – user10056563
  8 hours ago
  

  
  
  
  


• 
  
  
  

  
  

  
  
  
  
  
  

  
  
  @user10056563 Because that's the closest number to 4.4e10 that can be stored in a 32 bit float.
  
  – dbush
  8 hours ago
  

  
  
  
  

add a comment
 | 

You're actually printing the values of two different types here.

In the first case you're assigning a value to a variable of type float. The precision of a float is roughly 6 or 7 decimal digits, so unless the value can be represented exactly you'll see the closest value that can be represented by that type.

In the second case you're passing the constant 4.4e10 which has type double. This type has around 16 decimal digits of precision, and the value is within that range, so the exact value is printed.

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

dbushdbush

114k1515 gold badges129129 silver badges162162 bronze badges

share|improve this answer

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

dbushdbush

114k1515 gold badges129129 silver badges162162 bronze badges

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

edited 7 hours ago

JL2210

4,56644 gold badges1212 silver badges4242 bronze badges

answered 8 hours ago

dbushdbush

114k1515 gold badges129129 silver badges162162 bronze badges

answered 8 hours ago

dbushdbush

114k1515 gold badges129129 silver badges162162 bronze badges