How to extract digits after decimal point in float and store in char Array

Question

I refered below question but I need to extract the digits after decimal and store in char *array

1.How to store float in array of float[]

Ex:

 float = 1.24456

My length of char *array is 2

Expected Output:

array[0] = 2;
array[1] = 4;
array[2] = 4;

I need to implement this in C dynamically.

If the value was very close, but less than `1.244`, like `1.243999`, would you want `243` or `244`? — chux - Reinstate Monica, Jan 28 '19 at 19:27
@coder `1.24456` cannot be exactly represent by most `float`, Then the best approach differs, if you want 3 digits from the exact value of the `float` or one rounded to 3 decimal places. — chux - Reinstate Monica, Jan 28 '19 at 19:41

Govind Parmar · Accepted Answer · 2023-06-24T01:07:35.243

4

You can isolate the fractional part of a float by using the function modff in <math.h>, which returns the fractional part as the function's return value and the whole-number part as an argument by reference:

float f = 3.141592f;
float numpart, fracpart;
fracpart = modff(f, &numpart);

Once you're done that, you can create a string with a conventional string-building function:

char buf[100];
snprintf(buf, 100, "%f", fracpart);

Another option is converting the entire float to a string, and then using strchr(float_str, '.') to isolate the decimal part:

char floatbuf[100], decibuf[100], *p;
float f = 3.141592f;

snprintf(floatbuf, 100, "%f", f);
if ((p = strchr(floatbuf, '.')) != NULL)
{
    strcpy(decibuf, p + 1);
    puts(decibuf);
}

edited Jun 24 '23 at 01:07

answered Jan 28 '19 at 17:11

Govind Parmar

20,656
7
53
85

"converting the entire float to a string," --> may need a fairly long string, easily more than 20. – chux - Reinstate Monica Jan 28 '19 at 19:30
@chux Do you know off hand how many digits are storable in a 32-bit `float`? – Govind Parmar Jan 28 '19 at 19:32
1

Typically 24 significant binary digits. But I think you are looking for `FLT_MAX_10_EXP` "maximum integer such that 10 raised to that power is in the range of representable finite floating-point numbers" - often 37. Perhaps `char buf[1 + 1 + FLT_MAX_10_EXP + 1 + 6 + 1];` to cope with `-FLT_MAX`. No need to guess – chux - Reinstate Monica Jan 28 '19 at 19:34
1

Try `printf("%f", -FLT_MAX);` – chux - Reinstate Monica Jan 28 '19 at 19:36
@chux Yup - 48 chars. – Govind Parmar Jan 28 '19 at 19:38
Pedantic: note that `strchr(float_str, '.')` will return `NULL` with infinity/NaN. – chux - Reinstate Monica Jan 28 '19 at 19:39
@chux Correct, but failing to check the return value of `strchr` for `NULL`, regardless of input, is bad coding – Govind Parmar Jan 28 '19 at 19:41
Note: If the factional part if used as in `snprintf(buf, 100, "%f", fracpart);`, 9 should be enough: `"-.xxxxxx"` or less in OP's case of `char *array is 2`. – chux - Reinstate Monica Jan 28 '19 at 19:44

score 0 · Answer 2 · 2019-01-28T17:35:53.553

Slightly more mathematical approach, but arguably less flexible would be this:

#include <stdio.h>
#include <math.h>

int main()
{
    float num = 1.24456;
    int num_noDecimals = (int)num; //truncate decimals in original number
    float num_onlyDecimals = num - (float)num_noDecimals; //obtain only the number after decimal
    int x = 4; //number of digits past decimal to extract
    num_onlyDecimals = num_onlyDecimals*pow(10,x); //move extracting digits left of decimal
    int digits_forArray = (int)num_onlyDecimals; //truncate remaining digits right of decimal
    char arr[x];
    for(int i=x-1; i > -1; i--) { arr[i] = (char)(digits_forArray%10); digits_forArray = digits_forArray/10; }
    for(int i=0;i<x;i++) { printf("arr[%d] = %d\n",i,arr[i]); }
}

Hopefully it's commented well enough to understand the steps being taken here.

`(int)num` is undefined behavior unless `num` is near the range of `int`. — chux - Reinstate Monica, Jan 28 '19 at 19:28

score 0 · Answer 3 · answered Jun 26 '21 at 14:52

In my code, I removed the integer part, then I reverse the float part to integer part by multiply each number of the float part by the number 10 then I classify each digit of in the array

My code :

int main()
{
    float n = 1.2445601;
    int m=(int)n;
    float p=n-m;
    int x=7,i=0,tab[x];
    while(i<x)
    {
        p=p*10;
        i++;
    }
    i=6;
    while((int)p!=0)
    {
        tab[i--]=(int)p%10;
        p=p/10;
    }

    for(int k=0;k<x;k++)
    {
         printf("\narray[%d] = %d ;",k,tab[k]);
    }
    printf("\n");
    return 0;
}

Helper · Answer 4 · 2021-06-26T11:46:08.770

-2

If you just want the digits after the decimal point in variable, you could just have number - floor(number)

for example, if your number was 3.25, the calculation would be 3.25 - 3. This will give 0.25

edited Jun 26 '21 at 11:46

answered Jun 26 '21 at 11:31

Helper

1
1

1

This answer is just plain wrong, and has nothing to do with the question. I would recommend removing it. – GuedesBF Jun 29 '21 at 11:18

How to extract digits after decimal point in float and store in char Array

4 Answers4