printf() in C: How do I keep my floats/double from rounding?

Question

Been trying to get the outputs to give me the number without rounding, not sure what I'm missing

float NumberOfTrees1; for (NumberOfTrees1 = 1000.0; NumberOfTrees1 >= 50; NumberOfYears++) { NumberOfTrees1 = NumberOfTrees1 - (NumberOfTrees1 * 0.13); printf("Number of Remaining Trees: %0.1f\n",NumberOfTrees1); }

My Output:

Number of Remaining Trees: 61.7 Number of Remaining Trees: 53.7 Number of Remaining Trees: 46.7

Required Output:

Number of Remaining Trees: 61 Number of Remaining Trees: 53 Number of Remaining Trees: 46

I understand that the %0.1f is what gives me the .7 but when I use %0.0f it rounds up my numbers which I don't want. Been switching things around from using int, double, long float etc to no avail.

Any help would be great and thank you in advance!!!

By subtracting n*0.13 you're likely to have decimals. What don't you want: 46.7 rounded up to 47 or down to 46, or both? — Déjà vu
– Déjà vu, Commented Mar 20, 2021 at 5:42
double (and float) itself is rounded naturally (0.1 + 0.2 results in a rounded 0.3)... but just use "%a" to print all the bits (in hexadecimal): printf("0.3 rounded is %a\n", 0.1 + 0.2); — pmg
– pmg, Commented Mar 20, 2021 at 9:06

Andy Sukowski-Bang · Accepted Answer · 2021-03-20 16:55:09Z

Antonin GAVRELs answer should print the desired output, but if you don't want to cast the floating point numbers into integers, you could use the double floor (double x) function from <math.h>.

#include <math.h> #include <stdio.h> int main(void) { double x = 53.7; double floored = floor(x); printf("⌊%0.1lf⌋ = %0.1lf\n", x, floored); return 0; }

The program can be compiled with -lm and prints the following when executed:

⌊53.7⌋ = 53.0

Andrew Truckle · Accepted Answer · 2021-03-20 17:05:45Z

0

You can cast into int in order to truncate your number:

int main(void) { double d = 53.7; float f = 46.7f; int a = (int)d; int b = (int)f; printf("%d %d\n", a, b); }

output:

53 46

Or, as suggested by @user3386109, you may use floor(), but you will need to also include <math.h> header and compile with -lm

edited Mar 20, 2021 at 17:05

Andrew Truckle

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answered Mar 20, 2021 at 5:41

Antonin GAVREL

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9 Comments

BuddhaPowers Over a year ago

Is there any other way other than casting it into "int"? I'm taking a class and we haven't covered that as well as using floor(). Thank you though

Antonin GAVREL Over a year ago

you can use floor function from libc which truncates the number

Andy Sukowski-Bang Over a year ago

Why do you use the suffix f on the float? It's only needed on the double.

phuclv Over a year ago

Casting to int won't work if the float value is outside int's range. The only safe way is floor

user5550963 Over a year ago

UPVOTE for an answer!!!!! Quick and dirty way of doing this, my only suggestion is, put the NOTE: If you know that your value is larger than MAX_INT cast it to long or long long instead. What if you do not have math library?

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