Question

i need to calculate the age then in c programming how can i do “user input filtering” at scanf.

 main()
 {
 scanf("%d %d %d ,month,date, year);
 --------;
 printf("your age is"...);
 }

here the user can enter alphabets or some symbols how to filter them in c?

Answer 1

If by filtering, you mean remove the offending characters, you can either read lines in buffers and inspect them, or use a quick hack like this:

scanf("%d%*[^0-9]%d%*[^0-9]%d", &month, &day, &year);

where the * after % means to read and throw away and the ^0-9 in brackets means any character that is not 0 through 9. Possible pitfall: if the first character is unwanted, scanf fails. If you put a %*[^0-9] in the beginning, then input beginning with a number fails.

Alternatively, ask the user for proper input in case of failure (in previous case also you should check for the return value of scanf):

while (scanf("%d %d %d", &month, &day, &year) != 3)
{
    printf("bad input! Retry\n");
    /* possibly flush the line: */
    while (!feof(stdin) && fgetc(stdin) != '\n');
}