http://kor.i2p/books/The%20C%20Programming%20Language%20by%20K&R/chapter1.html
Nevertheless, writing
floating-point constants with explicit decimal points even when they have
integral values emphasizes their floating-point nature for human readers. The detailed rules for when integers are converted to floating point are in Chapter 2 . For now, notice that the assignment fahr = lower; and the test while (fahr < = upper) also work in the natural way - the int is converted to float before the operation is done.