If the serial received data is stored in a array inData[index] and then if strtok function is performed wont the data be
available as seperate charecters and not as a single string to perform atof function??
inData[index] is an array element, not an array. It is important to keep the terminology straight.
strtok() returns a pointer to a portion of the string that is being parsed. If inData contains "Joe is a small monkey" and strtok() is called, with a delimiter set containing just a space, strtok() will return a pointer that points to "Joe".
If inData contains "123.456 789.123 876.543", and strtok() is called, with a delimiter set containing just a space, strtok() will return a pointer that points to "123.456", which, obviously, atof() will easily handle.