1. Improved Code

Code that performs the same function can be written in various ways. For example, let's write a code that performs the same action using a for loop.

#include <stdio.h>

/* Code to print the Celsius-Fahrenheit temperature conversion table */

main() {
    int fahr;

    for (fahr = 0; fahr <= 300; fahr = fahr + 20) {
        printf("%3d %6.1f\n", fahr, (5.0 / 9.0) * (fahr - 32.0));
    }
}

When executed through a compiler, this code produces the same results as the code using the while loop written in section 1.2. However, there are several changes.

First, all variables except for the fahr variable representing Fahrenheit temperature have been removed. The lower and upper variables were integrated into the for loop, and the conversion formula is inserted directly as arguments in the printf statement instead of assigning it to a variable.

One fact we can ascertain here is that wherever a variable of a specific type's value can be used, any complex calculation that results in the same type can also be inserted. For instance, the third argument in the printf function of the code above contains a floating-point value, regardless of whether it is a single floating-point variable or a computed value from multiple variables.

Reducing the number of variables does not have significant performance implications since saving memory on that scale is rarely necessary. However, the code has become much simpler.

Of course, variable names also serve to indicate the purpose of the numbers. If upper = 300, it becomes clear to the reader that 300 serves as an upper limit. Considering this aspect, the code written like this may be harder to understand.

However, this issue can also be resolved by utilizing #define, which will be discussed later.

2. Explanation of the for Loop

The final aspect of the code to be explained pertains to the for loop. The for loop is another form of iteration. The structure of a for loop is as follows:

for(initialization; continuation condition; increment){
    Code to be executed at each step
}

Looking at it step-by-step, the initialization part sets the initial condition of the loop. In this case, it initializes fahr=0, setting the Fahrenheit temperature to 0.

The continuation condition specifies the condition under which the loop should continue. Here, it is fahr<=300; when this condition evaluates to false, the code within the braces will not be executed. Conversely, the code within the braces will continue to execute as long as this condition remains true.

If nothing is properly handled in the increment section such that fahr remains below 300 (for example, mistakenly increasing a different variable instead of fahr, or reducing fahr), the code within the braces will execute infinitely.

The increment section determines what action to perform each time a step is executed. In this case, it is fahr=fahr+20, which means that during each execution of the code within the braces, the fahr variable is increased by 20.

Although it is called an increment, this term is an abstract translation and can represent any action performed during each step of the iteration. It could decrease fahr, multiply it by 2, assign a different variable's value, or anything else, provided that the code is generally written to ensure that the loop will eventually terminate.

In summary, a for loop initializes a variable, performs some action each time the code within the braces executes, and moves closer to meeting the exit condition.

There is no rigid principle dictating whether to use while or for; simply choose the one that makes the code clearer and easier to understand.