learn through suffering C language
learn through suffering C language
Input validation
Post-assessment and pre-assessment
C has three loop statements in total.
It's about while loops, for loops, and do-while loops.
While and for loops have already been explained.
Actually, do-while loops are almost identical to while loops.
do-while statements are generally used in the following format:
The meaning and behavior of a conditional statement are exactly the same as those of a while statement.
In other words, it repeats the execution of the loop statement as long as the condition is true.
Furthermore, as a difference in notation, in the case of do-while statements,
A semicolon ; is required after the condition expression in a while statement.
The only difference between a do-while loop and a while loop is
The difference lies in whether the conditional statement is evaluated after the fact or in advance.
A while loop evaluates a condition before executing the statements within the loop.
However, the do-while loop evaluates the condition *after* the block of code it repeats has been executed.
Actually, it doesn't make that much of a difference.
In fact, a while loop and a do-while loop can sometimes produce the same result.
Therefore, do-while loops are not frequently used.
However, do-while loops have one significant advantage.
That's because a loop is guaranteed to execute at least once.
In the case of a while loop, if the condition is initially false,
It will end without the loop ever being executed.
With a do-while loop, the code block will always execute at least once.
It's about while loops, for loops, and do-while loops.
While and for loops have already been explained.
Actually, do-while loops are almost identical to while loops.
do-while statements are generally used in the following format:
do-while loop
do {
Loop Sentence;
} while (conditional expression);The meaning and behavior of a conditional statement are exactly the same as those of a while statement.
In other words, it repeats the execution of the loop statement as long as the condition is true.
Furthermore, as a difference in notation, in the case of do-while statements,
A semicolon ; is required after the condition expression in a while statement.
The only difference between a do-while loop and a while loop is
The difference lies in whether the conditional statement is evaluated after the fact or in advance.
A while loop evaluates a condition before executing the statements within the loop.
However, the do-while loop evaluates the condition *after* the block of code it repeats has been executed.
Actually, it doesn't make that much of a difference.
In fact, a while loop and a do-while loop can sometimes produce the same result.
Therefore, do-while loops are not frequently used.
However, do-while loops have one significant advantage.
That's because a loop is guaranteed to execute at least once.
In the case of a while loop, if the condition is initially false,
It will end without the loop ever being executed.
With a do-while loop, the code block will always execute at least once.
Input validation
The advantage of a do-while loop is that it guarantees at least one execution.
Above all, it really shines when it comes to input validation.
For example, let's try creating a program to calculate the area of a circle.
The area of a circle is radius times radius times pi.
Here, we're checking that the radius isn't a negative value, as that wouldn't make sense.
Next, let's check the case without using loops.
When running this program with an input of 8, the result is as follows:
The result of running this program with the input -8 is as follows.
While this technically checks out, it's a bit unfriendly.
If the input is incorrect, let's have them re-enter it.
The following program is an example of re-entrancy implemented with a while loop.
When running this program with the inputs -8, -5, and 8, the results are as follows:
The retyping was flawlessly done.
However, the problem lies with the program this time.
Looking at the program, I can see that the scanf function is being used twice.
Writing the `scanf` function twice for the same data input is truly wasteful.
The following program is an example of eliminating this waste with a do-while loop.
When running this program with the inputs -8, -5, and 8, the results are as follows:
This time, you only need to write the scanf function once.
The advantage of the do-while loop, which guarantees execution at least once, is being utilized.
Above all, it really shines when it comes to input validation.
For example, let's try creating a program to calculate the area of a circle.
The area of a circle is radius times radius times pi.
Here, we're checking that the radius isn't a negative value, as that wouldn't make sense.
What is pi?
In computing, pi is calculated as 3.14159. This is because extending it to the next digit gives 3.141592, and rounding down between 9 and 2 does not introduce significant error.
Next, let's check the case without using loops.
do-while loop
#include <stdio.h>
int main(void)
{
int r;
double s;
printf("Radius?:");
scanf("%d", &r);
if (r < 0) {
printf("The radius cannot be a negative value.\n");
} else {
s = r * r * 3.14;
printf("The area is %f.\n", s);
}
return 0;
}When running this program with an input of 8, the result is as follows:
Results
Radius?: 8 Value entered
The area is 200.960000.
The area is 200.960000.
The result of running this program with the input -8 is as follows.
Results
Radius?:-8 Input value
Radius cannot be negative.
Radius cannot be negative.
While this technically checks out, it's a bit unfriendly.
If the input is incorrect, let's have them re-enter it.
The following program is an example of re-entrancy implemented with a while loop.
do-while loop
#include <stdio.h>
int main(void)
{
int r;
double s;
printf("Radius?:");
scanf("%d", &r);
while (r < 0) {
printf("Radius?:");
scanf("%d", &r);
}
s = r * r * 3.14;
printf("The area is %f.\n", s);
return 0;
}When running this program with the inputs -8, -5, and 8, the results are as follows:
Results
Radius?:-8 Value entered
Radius?:-5 Value entered
Radius?:8 Value entered
The area is 200.960000.
Radius?:-5 Value entered
Radius?:8 Value entered
The area is 200.960000.
The retyping was flawlessly done.
However, the problem lies with the program this time.
Looking at the program, I can see that the scanf function is being used twice.
Writing the `scanf` function twice for the same data input is truly wasteful.
The following program is an example of eliminating this waste with a do-while loop.
do-while loop
#include <stdio.h>
int main(void)
{
int r;
double s;
do {
printf("Radius?:");
scanf("%d", &r);
} while (r < 0);
s = r * r * 3.14;
printf("The area is %f.\n", s);
return 0;
}When running this program with the inputs -8, -5, and 8, the results are as follows:
Results
Radius?:-8 Value entered
Radius?:-5 Value entered
Radius?:8 Value entered
The area is 200.960000.
Radius?:-5 Value entered
Radius?:8 Value entered
The area is 200.960000.
This time, you only need to write the scanf function once.
The advantage of the do-while loop, which guarantees execution at least once, is being utilized.
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Learning C language through suffering (Kushi C) isThis is the definitive introduction to the C language.
It systematically explains the basic functions of the C language.
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