C programming language (2nd Edition) -- Reading Notes -- 1.3

for sentence

A specific task can be programmed in many ways .

#include <stdio.h>
/* print Fahrenheit-Celsius table
for fahr = 0, 20, ..., 300; floating-point version */
main()
{
float fahr, celsius;
float lower, upper, step;
lower = 0; /* lower limit of temperatuire scale */
upper = 300; /* upper limit */
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;
}
}

The following is another program to convert Fahrenheit temperature to Celsius temperature .

#include <stdio.h>
main ()
{
    /* Print Fahrenheit temperature - Centigrade temperature */
int fahr;

for(fahr = 0; fahr<=300;fahr = fahr + 20)
    printf("%3d %6.1f\n" fahr, (5.0 / 9.0)*(fahr - 32));
}

         Improvements ：

1. Remove most variables , Just one int Type variable fahr;

2.for The lower temperature limit in the statement 、 Both the upper limit and the step size are constants ;

3. The expression for calculating the Celsius temperature becomes printf The third argument to the function , It is no longer a separate assignment statement .

        The last point of improvement is C A language General rules Example ： In any situation where a certain type of variable is allowed , More complex expressions of this type can be used . because printf The third argument to the function must be the same as %6.1f Matching floating point values , So you can use any floating-point expression here .

        for A statement is a circular statement , It's right while Generalization of sentences . take for Statements and while Statements are , Can be found for Statement operation is more intuitive . Parentheses contain 3 part , The parts are separated by semicolons . a ：

fahr = 0;

Is the initialization part , Execute only once before entering the loop . Two ：

fahr <=300;

It is the test or condition part of the control cycle . The loop control will evaluate this condition , If the result value is true （true）, Execution loop body . After that, it will be implemented Three parts ：

fahr = fahr + 20

To loop the variable fahr Add one step , And evaluate the condition again . If the calculated value is false （false）, The loop will terminate execution .

And while The sentence is the same ,for The body of a loop can be a statement , It can also be a group of statements locked by curly braces .

Initialization part （ a ）、 Condition part （ Two ） And increase the step length （ Third ） Can be any expression .

        In actual programming , Optional while And for Any circular statement in , It mainly depends on which one is clearer .for Statement is more suitable for the situation that initialization and increasing step size are both single statements and logically related , Because it puts the loop control statements together , And while More compact .

practice 1-5 Modify the procedure in the above section , In reverse order （ from 300 To 0 degree ） Print the temperature conversion table .