Exercise 1-15

The line celsius = (5.0/9.0) * (fahr-32.0); is where the conversion occurs. We can return this expression from a function called convert that takes in the floating-point value fahr as a parameter. Then, we assign the value of convert(fahr) to celsius within the loop.

    #include <stdio.h>
    
    float convert(float fahr);
    
    /* print Fahrenheit-Celsius table
        for fahr = 0, 20, ..., 300; floating-point version */
    main()
    {
        float fahr, celsius;
        int lower, upper, step;
    
        lower = 0;      /* lower limit of temperature table */
        upper = 300;    /* upper limit */
        step = 20;      /* step size */
    
        /* print Fahrenheit-Celsius table */
        fahr = lower;
        while (fahr <= upper) {
            celsius = (5.0/9.0) * (fahr-32.0);
            celsius = convert(fahr);
            printf("%3.0f %6.1f\n", fahr, celsius);
            fahr = fahr + step;
        }
        return 0;
    }
    
    /* convert:  convert fahrenheit temperature to celsius */
    float convert(float fahr)
    {
        return (5.0/9.0) * (fahr-32.0);
    }