Take a look here to get you started.
https://www.geeksforgeeks.org/implementitoa/
Code below is from the link above.
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41  // Implementation of itoa()
char* itoa(int num, char* str, int base)
{
int i = 0;
bool isNegative = false;
/* Handle 0 explicitely, otherwise empty string is printed for 0 */
if (num == 0)
{
str[i++] = '0';
str[i] = '\0';
return str;
}
// In standard itoa(), negative numbers are handled only with
// base 10. Otherwise numbers are considered unsigned.
if (num < 0 && base == 10)
{
isNegative = true;
num = num;
}
// Process individual digits
while (num != 0)
{
int rem = num % base;
str[i++] = (rem > 9)? (rem10) + 'a' : rem + '0';
num = num/base;
}
// If number is negative, append ''
if (isNegative)
str[i++] = '';
str[i] = '\0'; // Append string terminator
// Reverse the string
reverse(str, i);
return str;
}
