Thread: Help me to optimize this code

Hi..

Depends on whats needed, the question says display input and you do that " enter number:7 " so is displaying the numbers again needed..? if not, you don't need a Printf.. and you can use the one "for Loop". Then it comes down to, do you want the answer formatted and looking pretty or just Input displayed Y found/Not Found..?

Code:

#include <stdio.h>
int main() {
 int x[5];
 int i;
 int y=10;

 printf("\n Enter 5 numbers: ");
 scanf("%d%d%d%d%d",&x[0],&x[1],&x[2],&x[3],&x[4]);

 for (i=0;i<5;i++) {
  if (x[i]==y) {
   printf("\nFound");
   return 0;
     }
    }
    printf("\n Not Found");
 return 0;
}

Originally Posted by JohnGM

Code:

…
    scanf("%d%d%d%d%d",&x[0],&x[1],&x[2],&x[3],&x[4]);
…

I hope this is a joke.
What you think make this line?

You could do the same thing with

Code:

scanf("%5d",x)

Originally Posted by JohnGM

Hi ..

WoodSTokk........we can all make smart comments.....I am here to learn.....I am looking for your contribution but can't find it..?

John

Ops. I realy think thats a joke. Sorry.

To the problem.
The format "%d%d%d%d%d" expect 5 numbers in a row without delimiter.
Asume we enter "1234567890". What numbers will scanf read in the variables?
It can be 1, 2, 3, 4 and 567890 ... or 123456, 7, 8, 9 and 0 ... nobody knows.
It is better to use a delimiter.
In this example, i use space as delimiter:

Code:

…
        scanf(" %d %d %d %d %d", &x[0], &x[1], &x[2], &x[3], &x[4]);
…

Asume we enter "12 34 56 78 90".
Now we can enter 5 numbers and scanf see where one number begin and where it end.

But there is another problem. It dosn't matter what we enter, scanf is allways happy.
If we enter "12 34 56", scanf assign 12 to x[0], 34 to x[1] and 56 to x[2].
x[3] and x[4] will leave unchanged (they have garbage values since declaration).
For this case we can use the return value of scanf.
scanf returns the number of successfully assigned elements.
In our case, we want 5 numbers, so scanf should return 5.
Is this not the case, the input was not correct.
The result is:

Code:

…
    int x[5], ret;
…
    do {
        ret = scanf(" %d %d %d %d %d", &x[0], &x[1], &x[2], &x[3], &x[4]);
    } while (ret != 5);

Originally Posted by KBriggs

You could do the same thing with

Code:

scanf("%5d",x)

No, you cannot. The "5" in "%5d" specifies the field width, e.g., if the user entered "123456", it will match "12345". Nonetheless, the format specification only matches for a single int, i.e., the first int in the array since x is converted to a pointer to its first element.

Originally Posted by WoodSTokk

The format "%d%d%d%d%d" expect 5 numbers in a row without delimiter.
Asume we enter "1234567890". What numbers will scanf read in the variables?
It can be 1, 2, 3, 4 and 567890 ... or 123456, 7, 8, 9 and 0 ... nobody knows.
It is better to use a delimiter.

No, while I do prefer to insert such spaces, JohnGM's code is fine in this respect:

Originally Posted by C11 Clause 7.21.6.2 Paragraphs 5, 7, 8, 15a

A directive composed of white-space character(s) is executed by reading input up to the first non-white-space character (which remains unread), or until no more characters can be read. The directive never fails.

(...)

A directive that is a conversion specification defines a set of matching input sequences, as described below for each specifier. A conversion specification is executed in the following steps:

Input white-space characters (as specified by the isspace function) are skipped, unless the specification includes a [, c, or n specifier.

(...)

Trailing white space (including new-line characters) is left unread unless matched by a directive.

Therefore, it does not matter that there are no spaces separating the "%d": scanf will read "1234567890" as matching the first "%d". The format string will still correctly match say, "12 34 56 78 90".

Personally though, I would have kept to the idea of a loop from the original code rather than hard coding the five "%d" in a single format string.

Okay, the "%d" format skip whitespaces automaticly, so we can write the format "%d%d%d%d%d".
But this those not check if 5 numbers entered and without checking, the program runs with garbage values.

@laserlight: yes, the loop in post #1 was for me also nice and clear. I don't know, why JohnGM has changed this snippet.