OOP344 Challenge 2: myPrint function

The challenge can be found here.
Below is my solution.

#include "biof.h"
#include "<"string.h">"
#include "<"stdio.h>"
#include "<"stdarg.h>"
#include "<"stdlib.h>"

char* toUpperCase(char* str){
  int i = 0;
  for(i = 0; i < strlen(str); i++)
    if(str[i] >= 'a' && str[i] <= 'z')
      str[i] -= 32;
  return str;
}

char* myItoa(int val, char* str){
  int i;
  int j;
  int length;
  int scale;

  if (val == 0){
    str[0] = '0';
    str[1] = '\0';
  }
  else{
    for (i = 1, length = 0; val / i != 0 ; i *= 10, length++);
    if (val > 0) {
      for (i = 0; i < length; i++){
        scale = 1;
        for (j = 0; length - j > i + 1; j++)
          scale *= 10;
        str[i] = (val / scale) % 10 + 48;
      }
      str[i] = '\0';
    }
    else {
      val *= -1;
      str[0] = '-';
      for (i = 0; i < length; i++){
        scale = 1;
        for (j = 0; length - j > i + 1; j++)
          scale *= 10;
        str[i+1] = (val / scale) % 10 + 48;
      }
      str[i+1] = '\0';
    }
  }

  return str;
}

char* myFtoa(double val, char* str){
  int decPart = ((int)(val * 100)) % 100;
  int intPart = (int)val;
  int roundPos = ((int)(val * 1000)) % 10;

  char dot[2] = ".";
  char decStr[3] = "";
  char intStr[20] = "";

  if(roundPos >=5)
    decPart++;

  myItoa(decPart, decStr);
  myItoa(intPart, intStr);
    
  strcpy(str,"");
  strcat(str, intStr);
  strcat(str, dot);
  strcat(str, decStr);

  return str;
}

void bio_putint(int val){
  char temp[20] = "";
  bio_putstr(myItoa(val, temp));
}

int myPrint(const char* msg, ...){
  int i = 0;
  int num = 0;
  char buf[100];
  int dTemp;
  int hTemp;
  double fTemp;
  char cTemp;
  const char* strTemp;


  va_list args;
  va_start(args, msg);


  for(i = 0; i < strlen(msg); i++)
    if(msg[i] == '%' && 
      (msg[i+1]=='b' || msg[i+1]=='c' || msg[i+1]=='f' || 
       msg[i+1]=='s' || msg[i+1]=='x' || msg[i+1]=='X') )
      num++;

  for(i = 0; i < strlen(msg); i++){
    if(msg[i] != '%')
      bio_putch(msg[i]);
    else if(msg[i] == '%'){
      buf[0] = 0;
      switch(msg[i+1]){
      case 'd': dTemp = va_arg(args, int);
        bio_putint(dTemp);
        i++;
        break;
      case 'c': cTemp = va_arg(args, char);
        bio_putch(cTemp);
        i++;
        break;
      case 'x': hTemp = va_arg(args, int);
        itoa(hTemp, buf, 16);
        bio_putstr(buf);
        i++;
        break;
      case 'X': hTemp = va_arg(args, int);
        itoa(hTemp, buf, 16);
        bio_putstr(toUpperCase(buf));
        i++;
        break;
      case 'f': fTemp = va_arg(args, double);
        bio_putstr(myFtoa(fTemp, buf));
        i++;
        break;
      case 's': strTemp = va_arg(args, const char*);
        bio_putstr(strTemp);
        i++;
        break;
      default: 
        bio_putch(msg[i]);
        break;
      }
    }
  }

  va_end(args);
  return num;
}

int main(){
  int howMany;
  bio_init();
  howMany = myPrint("int %d, char %c, string %s, hex %X, float %f.\n", -56, 'M', "OOP344", 12, 12.34567);
  myPrint("Printed %d parameter(s)", howMany);
  bio_getch();
  bio_end();
  return 0;
}

Tested under VCC and BCC.
output is:
int -56, char M, string OOP344, hex C, float 12.35.
Printed 5 parameter(s)

I add a logical control that can round the decimal value. For example: 3.675 will be printed 3.68, while 5.321 will be printed 5.32.