float aFloat;
unsigned char *pBytes;
pBytes = (unsigned char * )&aFloat;
pBytes[3] = _buffer[_offset++];
pBytes[2] = _buffer[_offset++];
pBytes[1] = _buffer[_offset++];
pBytes[0] = _buffer[_offset++];
return aFloat;

Assume that _buffer is your byte array or pointer to an unsigned char *, and that _offset is the offset in your data.

To read an integer value:

int i = ((_buffer[_offset]<<24)|(_buffer[_offset+1]<<16)|(_buffer[_offset+2]<<8)|(_buffer[_offset+3]));
_offset+=4;
return i;