C language doesn't scan variable after reading string or char when int required

Question

C language doesn't scan variable after reading that variable as string(or char) instead of integer But the most weird is that it is entering in infinite loop


int main( ){
    int answer;
    printf("Hello\n");

    while (answer != 3){
        scanf("%d",&answer);
        switch (answer) {
            case 3:
                break;
            default:{
                printf("Invalid input\nTry again\n\n");
                break;}
        }
    }

    return 0;
}

To find how C language works and fix the problem

Side note: `int answer; ... while (answer != 3){` The `answer` variable is uninitialized the first time. — 001, Mar 07 '23 at 20:40
The problem is when I try to read string or char otherwise it runs correctly — Mihai, Mar 07 '23 at 20:43
What *does* `start()` use? The MRE means we don't have to keep asking questions. — Weather Vane, Mar 07 '23 at 20:47
but when enter string it doesnt read my scanf and enter a infinite loop printing only case 3 code — Mihai, Mar 07 '23 at 20:49
[scanf() leaves the newline character in the buffer](https://stackoverflow.com/questions/5240789/scanf-leaves-the-newline-character-in-the-buffer) may explain the reason you're having trouble reading char or string variables. It isn't exactly clear what trouble you're having. — Retired Ninja, Mar 07 '23 at 20:53
@Barmar: Re “FYI you don't need a block around each `case` body”: It is a useful practice for preventing identifiers declared in one `case` segment from polluting others, so it should not be discouraged. — Eric Postpischil, Mar 07 '23 at 20:55

score 0 · Accepted Answer · answered Mar 07 '23 at 20:52

0

You can add one more statement under the label default to avoid an infinite loop when a non-number is entered

        default: {
            printf( "Invalid input\nTry again\n\n" );
            scanf( "%*[^\n]" );
            break; }
        }

If the user will try to interrupt the input you can also write

if ( scanf("%d",&answer) == EOF ) break;

to exit the while loop.

Pay attention to that the variable answer shall be initialized before the while loop.

answered Mar 07 '23 at 20:52

Vlad from Moscow

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But why it doesn't read my first scanf. It is only for my better understanding – Mihai Mar 07 '23 at 20:58
1

@Mihai I have not understood what you mean by the first scanf. If you enter a non-number then it is stored in the input buffer and you need to skip it. Otherwise a next call of scanf will try to read that non-number with the same result and you will have an infinite loop. – Vlad from Moscow Mar 07 '23 at 20:59
Если ты разговариваешь на русском пожалуйста объясни почему при вводе строки просто перестает читать scanf. Тоесть объясни как именно происходит процесс для понимания.Еще раз спасибо за решение проблемы и если что не злись на мои тупые вопросы) – Mihai Mar 07 '23 at 21:10
@Mihai Если вы ввели не число, то оно не читается и остается во входном буфере. Следующий вызов scanf снова сталкивается с этим не числом и не может его прочитать, и в результате получается бесконечный цикл. – Vlad from Moscow Mar 07 '23 at 21:13
Значи при втором scanf он опять читает из буфера и не может прочесть и вы просто создали scanf который может прочесть из буфера. Огромное вам спасибо – Mihai Mar 07 '23 at 21:19

C language doesn't scan variable after reading string or char when int required

1 Answers1