whats wrong with this code?

**smahdi1991** · 11-01-2009

hello.
i am a complete beginner in C, so please bear with me .
well i wrote a simple program , but i have no idea why it is not working! its pretty simple you know !

here is my code

Code:

              //in the name of god

#include<stdio.h>
int main()
{
        int x,y;
        char c;
        printf("\nPlease Enter 2 operands and then your desigred operator(+/*)");
        scanf("%d%d%c",&x,&y,&c);
        
        printf("x = %d,,y = %d  Operator:%c\n",x,y,c);
        
        if (c == '*' )
        {
               printf("x * y = :%d",x*y);        
        }
        
        else if (c == '+' )
        {
               printf("x + y:%d",x+y);         
        }
        else
        printf("error happened!");

        return 0;
}

what is wrong with

Code:

scanf("%d%d%c",&x,&y,&c);

i noticed that if i write

Code:

scanf("%d%c%d",&x,&c,&y);

it would work perfectly! but i really dont know what is the difference between the two!
would anyone help me ?
thanks

**C_ntua** · 11-01-2009

Cause you are putting "3 3 +" and it reads " " as a character :P
If you put "3 3+" (without space) it works fine

**Kinshara** · 11-01-2009

why error because you scanf %d%d%s in one time,
the system would be confuse, which one is the first %d,the second, the third when you input at once..
how if you write the scanf 3 times?
so

Code:

scanf("%d",&(int variable));
scanf("%d",&(int variable));
scanf("%s",(stringvariable)); //or you can gets(variabelstring); also

**Elysia** · 11-01-2009

Do NOT use gets. Use fgets in such case.
To explain in better english, consider that you enter:
33+
scanf will think that 33 is actually one number, not two.
If you do, 3+3 on the other hand, it will think the first number is 3 (because there is a non-number afterwards) and then a character and later another number.
Make sense?

**Kinshara** · 11-01-2009

in my compiler(I use visual C), I can use that, because I use"fflush(stdin);"
so the other buffer from scanf, being erased..
I don't really know what your compiler is, but it's still same topic "C" code.. hehehe

**Elysia** · 11-01-2009

fflush stdin is BAD.
gets is also NASTY.
Avoid both.

**Kinshara** · 11-01-2009

hmmm I must use it,, or, when I run my program, it will out automaticly when I input..
any other idea? to avoid it?

**laserlight** · 11-01-2009

Originally Posted by Kinshara

in my compiler(I use visual C), I can use that, because I use"fflush(stdin);"
so the other buffer from scanf, being erased..
I don't really know what your compiler is, but it's still same topic "C" code.. hehehe

If you are talking about the use of gets(), then the problem is that you have no way of limiting the amount of input read. You have to trust that your users do not enter more input than you expect. Thus, you can use gets(), but you should not.

Likewise, you can use fflush(stdin), but it results in undefined behaviour, since fflush() is only defined for output streams and update streams whose most recent operation was not input. However, you can get away with fflush(stdin) on specific compilers (like the one that you are using), but your code will not be portable.

**Elysia** · 11-01-2009

Originally Posted by Kinshara

hmmm I must use it,, or, when I run my program, it will out automaticly when I input..
any other idea? to avoid it?

Yes, you can flush the input buffer. There are lots of examples on the board.

**Kinshara** · 11-01-2009

how can I flush the input buffer without useing fflush(stdin)?? can you show me example? or the link to the board?
sory if I disturb you

**Elysia** · 11-01-2009

C Board - Search Forums

**Kinshara** · 11-01-2009

is any negative site if we use fflush stdin for our computer?

**Elysia** · 11-01-2009

What does that mean? Does it have any bad effect on the computer or something? Is that what you are asking?

**Kinshara** · 11-01-2009

yeah..
sorry if my language is bad!..

**Elysia** · 11-01-2009

The problem is that it is undefined. No one knows that is going to happen if you use it.
Your code could crash. It might not work. It might work.
That is the beauty of undefined. So do not use it, quite simply put.

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