This program is presented as below.

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#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 %6.1fn", fahr, celsius);
        fahr = fahr + step;
    }
 
    return 0;
}

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 andcelsius 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

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fahr = lower;

and the test

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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, %sfor charater string, and %% for %itself.

Reference

The C Programming Language