CODEWITHSUNDEEP
cvalidationinteger
user2421843
user2421843

Reputation: 47

Validating Integer in C Programming

How can I make sure the number input by user is integer ranging from 0 to 4 only and also making sure that it is non negative/non symbol/alphabet??

If I do this,then it will not be able to validate alphabet/symbol

printf("Enter number 0 to 4");
scanf("%d",x);

if((x<0)||(x>4))
{
   printf("0 to 4 only");
   scanf("%d",x);
}
else
{
 xxxxxx
}

Upvotes: 0

Views: 461

Answers (2)

Jonathan Leffler
Jonathan Leffler

Reputation: 753505

If the input should be a single number on the line, then:

char line[4096];
int  x;

if (fgets(line, sizeof(line), stdin) == 0)
    ...EOF or other major trouble...
else if (sscanf(line, "%d", &x) != 1)
    ...not an integer...
else if (x < 0)
    ...negative - not allowed...
else if (x > 4)
    ...too large - maximum is 4...
else
    ...Hooray - number is valid in the range 0-4...use it...

You get to choose how the errors are handled. The first error handling should abandon the efforts to get a number from the user; the other three could warrant a retry (but keep an eye on how many retries you allow; if they get it wrong 10 times in a row, it is probably time to give up).

The key point is that the code uses fgets() to get the whole line, and then parses that. It would be possible to do further analysis — to make sure there isn't extra information on the line (so the user didn't type '3 dogs' instead of just '3'). This also allows you to report errors in terms of the whole line. The test for if (sscanf(line, "%d", &x) != 1) is also important. The members of the scanf()-family of functions report the number of successful conversion specifications (%d is a conversion specification). Here, if sscanf() successfully converts an integer, it will return 1; otherwise, it may return 0 or EOF (though EOF is unlikely with sscanf()). If there were 3 conversion specifications, the correct check would be != 3; it might report 1 or 2 successful conversions.

Upvotes: 2

md5
md5

Reputation: 23699

First %d format from scanf expects a pointer to int. So you will write:

scanf("%d", &x);

Then you can test whether the read data match with the format, using scanf return value:

if (scanf("%d", &x) != 1 || x < 0 || x > 4)
{
    /* Wrong input */
}
else
{
    /* Well-formed input */
}

Read man scanf for further informations.

Upvotes: 2

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