Why not write the code like this?

I bring this up because we recently encountered a bug. We need to transmit the battery level to BT, and then BT displays the level on the phone. A problem we encountered is that if we transmit 100% of the level, the actual level displayed is 0.

We use a function like this, which has 3 parameters.

#include <stdio.h>
#include <stdint.h>
#include <stdbool.h>


typedef unsigned char   uint08;
typedef unsigned short   uint16;
typedef long unsigned int  uint32;
typedef unsigned long long  uint64;
typedef unsigned int         uint;

#define nullptr (void*)(0)

/******************************************************************************
 * Descript: Converts a numeric value to a string in decimal format.
 * Params:
 *     @str[OUT]--Converts the value of the input buffer.
 *     @dec[IN]--Decimal value.
 *     @num[IN]--The number of conversions. (num<=10)
 *     @isDropZero[IN]--Whether to discard zero or not.
 * Return: The length of the converted string.Negative means failure.
 * Others: None.
*******************************************************************************/
const uint32 Pow10Array[] = {1, 10, 100, 1000, 10000, 100000, 1000000,
 10000000, 100000000, 1000000000};
int decToStr(char *str, uint32 dec, uint num, bool isDropZero)
{
 uint08 temp;
 uint32 value;
 char *pTemp;
 
 if(str == nullptr || num == 0) return 0;
 if(num > 10) num = 10;

 pTemp = str;
 while(num--) {
  value = dec/Pow10Array[num];
  temp = value%10;
  if(isDropZero && temp == 0) continue;
  if(isDropZero) isDropZero = false;
  *pTemp++ = '0'+temp;
 }
 if(pTemp == str) *pTemp++ = '0';

 return (pTemp-str);
}

int main()
{
    char buffer[64] = { };
    int indicators = 1;

    decToStr((char*)buffer, indicators, 3, true);
    printf("%s\n", buffer);

    return 0;
}

There is a num parameter in the function. If this parameter is not set correctly, it will be fatal. For example, if the number is 100 and I set this parameter to 2, the result will be like this.

The implementation of this function is quite good.

Of course, since it is a common problem.

But I wonder why they don't write code like this?

#include <stdio.h>

int main()
{
    char buffer[64] = { 0 };
    int indicators = 100;

    sprintf(buffer, "%d", indicators);

    printf("%s\n", buffer);

    return 0;
}