begineer for C program (RS 232)

Task: to get the data from the weight.
Example: 35.25kg, data from rs232 is “=52.53”

for (i=0; i<=20; i++)
{ printf ("%c
",(nIn=serCgetc()));} // get input char

But the data is read char by char and in reveser order.
How can I change to correct order?
Also, i need to have calcation by use of this value,
how can I change char –> char array / string –> nember?

I am beginner only and really dont know how to do?
please help me

thank thank thank