If you just want to round the number for output purposes, then the "%.2f" format string is indeed the correct answer. However, if you actually want to round the floating point value for further computation, something like the following works:
#include <math.h>
float val = 37.777779;
float rounded_down = floorf(val * 100) / 100; /* Result: 37.77 */
float nearest = roundf(val * 100) / 100; /* Result: 37.78 */
float rounded_up = ceilf(val * 100) / 100; /* Result: 37.78 */
Notice that there are three different rounding rules you might want to choose: round down (ie, truncate after two decimal places), rounded to nearest, and round up. Usually, you want round to nearest.
As several others have pointed out, due to the quirks of floating point representation, these rounded values may not be exactly the "obvious" decimal values, but they will be very very close.
For much (much!) more information on rounding, and especially on tie-breaking rules for rounding to nearest, see the Wikipedia article on Rounding.
Answer from Dale Hagglund on Stack OverflowIf you just want to round the number for output purposes, then the "%.2f" format string is indeed the correct answer. However, if you actually want to round the floating point value for further computation, something like the following works:
#include <math.h>
float val = 37.777779;
float rounded_down = floorf(val * 100) / 100; /* Result: 37.77 */
float nearest = roundf(val * 100) / 100; /* Result: 37.78 */
float rounded_up = ceilf(val * 100) / 100; /* Result: 37.78 */
Notice that there are three different rounding rules you might want to choose: round down (ie, truncate after two decimal places), rounded to nearest, and round up. Usually, you want round to nearest.
As several others have pointed out, due to the quirks of floating point representation, these rounded values may not be exactly the "obvious" decimal values, but they will be very very close.
For much (much!) more information on rounding, and especially on tie-breaking rules for rounding to nearest, see the Wikipedia article on Rounding.
Using %.2f in printf. It only print 2 decimal points.
Example:
printf("%.2f", 37.777779);
Output:
37.77
Limiting floating numbers to 2 decimal places - Processing 2.x and 3.x Forum
rounding - Round float to 2 decimal places in C language? - Stack Overflow
How can I change a float variable into one with strictly 2 decimal places?
[C] Truncating to 2 decimal places.
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It is necessary that the number be stored in a variable as number = 136.25
But that would be the incorrect result. The precise result of number + number * 0.1 is 136.26787141. When you round that downwards to 2 decimal places, the number that you would get is 136.26, and not 136.25.
However, there is no way to store 136.26 in a float because it simply isn't a representable value (on your system). Best you can get is a value that is very close to it. You have successfully produced a floating point number that is very close to 136.26. If you cannot accept the slight error in the value, then you shouldn't be using finite precision floating point arithmetic.
If you wish to print the value of a floating point number up to limited number of decimals, you must understand that not all values can be represented by floating point numbers, and that you must use %.2f to get desired output.
Round float to 2 decimal places in C language?
Just like you did:
- multiply with 100
- round
- divide by 100
I agree with the other comments/answers that using floating point numbers for money is usually not a good idea, not all numbers can be stored exactly. Basically, when you use floating point numbers, you sacrifice exactness for being able to storage very large and very small numbers and being able to store decimals. You don't want to sacrifice exactness when dealing with real money, but I think this is a student project, and no actual money is being calculated, so I wrote the small program to show one way of doing this.
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int main(void)
{
double number, percent_interest, interest, result, rounded_result;
number = 123.8798831;
percent_interest = 0.1;
interest = (number * percent_interest)/100; //Calculate interest of interest_rate percent.
result = number + interest;
rounded_result = floor(result * 100) / 100;
printf("number=%f, percent_interest=%f, interest=%f, result=%f, rounded_result=%f\n", number, percent_interest, interest, result, rounded_result);
return EXIT_SUCCESS;
}
As you can see, I use double instead float, because double has more precession and floating point constants are of type double not float. The code in your question should give you a warning because in
float number = 123.8798831;
123.8798831 is of type double and has to be converted to float (possibly losing precession in the process).
You should also notice that my program calculates interest at .1% (like you say you want to do) unlike the code in your question which calculates interest at 10%. Your code multiplies by 0.1 which is 10/100 or 10%.
I’m new to c and I would appreciate any kind of help
Hey there, really quick question...
How can I get my program to truncate a double to 2 decimal places NOT rounding it.
my printf statement looks like this right now:
printf("The amount entered is: %.2lf", input);Thanks.
What is the maximum decimal places that can be stored using c? I tried to store - 1.86264514923107200935514487085e-09 but only got 0.00000000186264514923107200000000.....