使用char和scanf以及for循环时遇到问题？

Question

My problem is using char and scanf. Below you can find my code that is almost working right. The problem is concerning the for loop. You see, I would like to ask 10 characters from the user, and count the alphabets, but for loop is not working properly. It dosent count the inputs right. For example, if the user types 6, it is fine, or a, it is also fine, but if he types for example 10 or 11, then the program thinks that the user typed 2 different character but when actually the user only typed one character "10". So please, help me, and explain, why the scanf whit the char isnt working properly. Thank you!

#include <stdio.h>
#include <stdlib.h>


unsigned int countalpha(void){

printf("Please enter 10 characters:\n");

char b;
int sum = 0;
int i = 0;

for (i = 0; i<10; i++)
    {
    scanf("%c\n", &b);


    if (isalpha(b))
        sum = sum +1;
    else
        sum = sum;

    }


    return sum;

}

int main()
{
    int sum;

    sum = countalpha();
    printf ("Letters totally: %d", sum);

    return 0;
}

Answer 1

The scanf() function is incredibly hard to use correctly.

Trailing white space in a scanf() format string is diabolical for interactive input. The notation "%c\\n" means 'read a character; then skip following white space until the next character that isn't white space, and only then return from the function'. This is seldom what you want. The user will need to type a character, perhaps a , and a return, and another one, and some blanks, and so on, but the input won't return until, in frustration, they type 'you stupid program' (and a newline), at which point everything suddenly starts working, except that their comment probably wasn't the correct response for the next input. Or they hit interrupt and never run your program again because it is too frustrating for them.

Note that any white space character in a scanf() format string means 'skip optional white space', which means blanks, tabs, newline (and sundry more obscure characters) are skipped if they are present, but there's no problem if there is no white space. Also note that the only conversion specifiers that don't skip white space anyway are %c , %[...] and %n ; all other conversion specifiers automatically skip white space.

You should probably be using " %c" . That means 'skip white space and then return the character that isn't white space'. Or, given your code, you can simply use "%c" , or even better just:

int c;
while ((c = getchar()) != EOF)
{
    if (isalpha(c)
        sum++;
}

If you want line oriented input, do not use scanf() or fscanf() ; use fgets() or getline() followed by sscanf() .

Incidentally, the lines:

else
    sum = sum;

are pretty pointless. The compiler will probably optimize them away, but other people shouldn't be forced to read them and puzzle over what you were thinking.

Answer 2

Is the user supposed to press ENTER between each character? Your format string "%c\\n" indicates that they should, but your problem statement suggests otherwise. Try removing the \\n .

Further points:

• scanf() returns the number of items parsed and assigned. You should always check this return to make sure that the expected number of items were assigned.
• The following code is pointless and should be removed:

    else
        sum = sum;