While loop in C prints the same line more than once

Question

char ch;
int nr=0;

printf("\n: "); 
ch = getchar();

while(ch != 'q' && ch != 'Q'){
    ch = tolower(ch);
    if(ch == 'a' || ch == 'e' || ch == 'o' || ch == 'i' || ch == 'u')
        nr++;
    
    printf("something");
    ch = getchar();
}
    
printf("vocale: %d", nr);

its supposed to count the number of vowels until the user presses q or Q. it's such a silly program and yet i cant get past it.

Please include a minimal reproducible example in your question. — mkrieger1
– mkrieger1, Commented Nov 1, 2022 at 19:55
Of course it prints "something" every time. You've told it to. — Chris
– Chris, Commented Nov 1, 2022 at 19:58
It likely prints them all at once because your IO is buffered and you haven't printed a newline. — Chris
– Chris, Commented Nov 1, 2022 at 19:59
@500-InternalServerError 'y' is not a proper vowel in the English language. (though I've seen others mistakenly include it -- must be like that "New Math" stuff) — David C. Rankin
– David C. Rankin, Commented Nov 1, 2022 at 20:22

Vlad from Moscow · Accepted Answer · 2022-11-01 20:11:53Z

1

Instead of using getchar

ch = getchar();

that also reads white space characters use scanf like

scanf( " %c", &ch );

Pay attention to the leading space in the format string. It allows to skip white space characters.

For example

while ( scanf( " %c", &ch ) == 1 && ch != 'q' && ch != 'Q'){

Also it will be more safer to write

ch = tolower( ( unsigned char )ch );

edited Nov 1, 2022 at 20:11

answered Nov 1, 2022 at 19:58

Vlad from Moscow

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Comments

Tenobaal · Accepted Answer · 2022-11-01 20:04:20Z

-1

The problem is, that the input only gets flushed to your program whenever the user presses enter. Another reason why it seems not to work is, because you don't have a newline at the end of you output (printf("vocale: %d", nr); ), which causes the output not to be flushed to the terminal when the program ends. Fix this and your program works, but maybe not as you expect it to, because you still have to press enter. It will still only count to the first 'q' found.

int main() {
    char ch;
    int nr = 0;
    printf(": "); 
    while(tolower(ch = getchar()) != 'q'){
        ch = tolower(ch);
        if(ch == 'a' || ch == 'e' || ch == 'o' || ch == 'i' || ch == 'u')
            nr++;
    }
    printf("vocale: %d\n", nr);
}

The program:

: aeu q oi (here I pressed enter)
vocale: 3

answered Nov 1, 2022 at 20:04

Tenobaal

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1 Comment

David C. Rankin Over a year ago

Just a note, the printf("vocale: %d", nr); after the close of the loop lacking a '\n' has nothing to do with streams not getting flushed (at that location). Streams are flushed and closed at program exit.

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