printf() presents weird results

Question

My code is this

#include<stdio.h>
int main(void)
{
    unsigned short height = 0;
    unsigned short width = 0;
    const unsigned short MIN_SIZE = 3;
    printf("Enter the values for the width and the height minimum of %u\n:",
           MIN_SIZE);
    scanf(" %hd %hd", &width, &height);
    if (width < MIN_SIZE)
    {
        printf("The value of width   %u is too small. I set this to %u    \n",
               width, MIN_SIZE);
        width = MIN_SIZE;
    }
    if (height < MIN_SIZE)
    {
        printf
            ("The value of height %u is too small. I setting this to   %u \n"),
            height, MIN_SIZE;
        height = MIN_SIZE;
    }
    for (unsigned int i = 0; i < width; ++i)
    {
        printf("*");
    }
    return 0;
}

When I give a width of 7 for example, and a height of 0, the printf() presents weird numbers. Can you explain please why this is happening?

Also, when you say that it presents 'weird results', what do you mean by that? — qaphla, Sep 10 '13 at 19:57
Not without knowing what the actual out put is, no, we can't. — DiMono, Sep 10 '13 at 20:03
What compiler do you use? Doesn't it give a "too few arguments for format" warning or similar? — Martin R, Sep 10 '13 at 20:09

score 6 · Answer 1 · edited May 23 '17 at 11:50

6

THis one would probably compile with a warning. You need to keep the closing parenthesis after providing all the argument.

printf
            ("The value of height %u is too small. I setting this to   %u \n"),
            height, MIN_SIZE;

Probably you meant:

printf("The value of height %u is too small. I setting this to   %u \n", height, MIN_SIZE);

The main issue is that we should use "%hu" for short intergers. I would try this:

#include<stdio.h>
int main(void)
{
    unsigned short height = 0;
    unsigned short width = 0;
    const unsigned short MIN_SIZE = 3;
    int i ;
    printf("Enter the values for the width and the height minimum of %u\n:", MIN_SIZE);
    scanf(" %hu %hu", &width, &height);
    if (width < MIN_SIZE) {
        printf("The value of width   %hu is too small. I set this to %hu    \n", width, MIN_SIZE);
        width = MIN_SIZE;
    }
    if (height < MIN_SIZE) {
        printf("The value of height %hu is too small. I setting this to %hu \n", height, MIN_SIZE);
        height = MIN_SIZE;
    }
    for (i = 0; i < width; ++i)
    {
        printf("*");
    }
    return 0;
}

There was a good related discussion on SO about this: What is the format specifier for unsigned short int?

edited May 23 '17 at 11:50

Community

1
1

answered Sep 10 '13 at 20:05

Manoj Pandey

4,528
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2

It does compile (comma operator), but any decent compiler should warn that there are more '%' conversions than data arguments. – Martin R Sep 10 '13 at 20:07
+1 for finding the problem. But interestingly, it will compile with the C99 standard in `gcc`. – lurker Sep 10 '13 at 20:08
I meant that when i set for example the width 7 and the height 0 printf() presenting correctly the width but in height prints something like 2476842 – paulakis Sep 10 '13 at 20:08
@Martin R, I agree (+1). I have updated the answer to be more accurate. – Manoj Pandey Sep 10 '13 at 20:09
I know that i can use integers but i want to know why compiler does that – paulakis Sep 10 '13 at 20:12
Thank you buddy.... I didn't see it before.... But the weird is that compiler started and doesn't hit any error – paulakis Sep 10 '13 at 20:14
`%hu` isn't necessary for `printf` (though it *is* necessary for `scanf`), since all arguments of type `char` and `short` (and their `unsigned` variants) get promoted to `int` or `unsigned int` when passed to variadic functions like `printf` due to the default argument promotions. – Adam Rosenfield Sep 10 '13 at 20:16
In scanf() i didn't write %hu but %hd... Is this wrong ? My book doesn't reference anywhere about "variadic" – paulakis Sep 10 '13 at 20:25
1

I would say yes. Since "%hd" is a short and "%hu" is an unsigned short . – Manoj Pandey Sep 10 '13 at 20:28
Do you want "... minimum of %hu\n:"? `%hu` – chux - Reinstate Monica Sep 11 '13 at 02:48

printf() presents weird results

1 Answers1