A program to print Fahrenheit-Celsius table with floating-point values

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Another
program to print Fahrenheit-Celsius table with decimal integer

This program is presented
as below.

#include <stdio.h>
/* print Fahrenheit_Celsius table
    for fahr = 0, 20, ..., 300; floating-point version */
int main()
{
    float fahr, celsius;
    int lower, upper, step;

    lower = 0;      /* lower limit of temperature table */
    upper = 300;     /* upper limit of temperature table */
    step = 20;       /* step size */

    fahr = lower;
    while (fahr <= upper)  {
        celsius = (5.0/9.0) * (fahr-32.0);
        printf("%3.0f %6.1f\n", fahr, celsius);
        fahr = fahr + step;
    }

    return 0;
}

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The figure of this program is presented as above. The right part of the figure is the output. This is much like the program which is mentioned at the beginning of the article, except that fahr and celsius are
declared to be float. We were unable to use 5/9 in the previous version because integer division would truncate it to zero. A
decimal point in a constant indicates that it is floating point, however, so 5.0/9.0 is not truncated because it is the ratio of two floating-point values.

If an arithmetic operator has integer operands, an integer operation is performed. If
an arithmetic operator has one floating-point operand and one integer operand, however, the integer will be converted to floating point before the operation is done. Writing floating-point constants with explicit decimal points even when
they have integral values emphasizes their floating-point nature for human readers.

For now, notice that the assignment

fahr = lower;  

and the test

while (fahr <= upper)

also work in the nature way — the int is converted to float before the operation is done.

The implications of width and precision are tabled as follows.

• %d            print as decimal integer
• %6d          print as decimal integer, at least 6 characters wide
• %f             print as foating point
• %6f           print as floating point, at least 6 characters wide
• %.2f          print as floating point, 2 characters after decimal point
• %6.2f        print as floating point, at leat 6 wide and 2 characters after decimal point

Among others, printf also recognizes %o for
octal, %x for hexadecimal, %c for
character, %s for charater string, and %% for % itself.

Reference

The C Progrmming Language