scanf char variable in between scanf integer variable doesn't work?

Question

I thought of making a calculator, just a simple one with loops and the basic operations, but the weird thing is that the scanf of character in between my scanf for number is being ignored. It works fine if I put it on top of the scanf of integer but it wouldn't look anything like a calculator. Is there any way to solve this issue? It's not yet finished; got an error up to here, so wondering what's wrong.

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

int main(){
    int number1,number2,total;
    char a;
    printf("This is your personal calculator:(End with ""="")\n");

    scanf("%d",&number1);
    scanf("%c",&a);
    scanf("%d",&number2);

    if (a == 'x' || a == 'X' || a == '*'){
        total=number1*number2;
        printf("%d",total);
    } else if (a == '/'){
        total=number1/number2;
        printf("%d",total);
    } else if (a == '+'){
        total=number1+number2;
        printf("%d",total);
    } else if (a == '-'){
        total=number1-number2;
        printf("%d",total);
    } else {
        printf("error");
    }

    system("pause");
    return 0;
}

You have to show how you are entering your numbers. I'm sure your calculator will work fine if you enter everything in one line without spaces, like `12+34`. But if you enter everything on a separate line, it is a different story. You have to include such important details in the question. — AnT stands with Russia, Nov 23 '13 at 18:58
Ity is also unclear why you tell the user to "end with =". Where, when and how is the user supposed to enter that "="? — AnT stands with Russia, Nov 23 '13 at 19:01

Jonathan Leffler · Answer 1 · 2014-02-17T15:20:59.647

You should test that you get a value from scanf(), every time.

The %c character reads the blank or newline after the first number; use " %c" with a leading space to skip over optional white space before reading the character.

if (scanf("%d", &number1) == 1 &&
    scanf(" %c", &a) == 1 &&
    scanf("%d", &number2) == 1)
{
    ...process possibly valid input...
}
else
{
    ...diagnostics...
}

It will probably be easier to give good diagnostics if you read whole lines with fgets() and parse them with sscanf().

Recommendation 1: show an example of what you type as input and what you get as output. This makes it easier for people to help you (they can tell whether the program is producing the same output for them).
Recommendation 2: echo your input so you can see what the program got. This allows you to tell whether the program got the input you expected. You'd probably find that number2 was not containing what you expected, for example.
Recommendation 3: initialize number1 and number2 to -1 so you can see when the scanf() failed (since you aren't yet checking whether scanf() succeeded).

score 1 · Answer 2 · answered Nov 23 '13 at 16:39

1

The problem is because of the newline char \n left over by the scanf. This could be avoided by placing a space before format specifier %c.

Try this

scanf(" %c", &a);  
       ^ An space

this will help you to eat up \n char left over by first scanf

answered Nov 23 '13 at 16:39

haccks

104,019
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176
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1

hi, thanks it solved the issue.. didnt know about it till now thanks – JMusicTouch Nov 23 '13 at 16:45
Your welcome. I glad that it helped you :) – haccks Nov 23 '13 at 16:46

score 0 · Answer 3 · answered Nov 23 '13 at 17:20

0

int main()

{

int number1,number2,total;
char a;
printf("This is your personal calculator:(End with ""="")\n");

scanf("%d",&number1);

fflush(stdin); // SIMPLE WAY FLUSH THE INPUT STREAM, INPUT BUFFER IS USUALLY CLEARED.
scanf("%c",&a);

scanf("%d",&number2);

if (a == 'x' || a == 'X' || a == '*'){
    total=number1*number2;
    printf("%d",total);
} else if (a == '/'){
    total=number1/number2;
    printf("%d",total);
} else if (a == '+'){
    total=number1+number2;
    printf("%d",total);
} else if (a == '-'){
    total=number1-number2;
    printf("%d",total);
} else {
    printf("error");
}

system("pause");
return 0;

}

answered Nov 23 '13 at 17:20

Rafed Nole

112
1
4
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It is illegal to apply `fflush` to `stdin`. `fflush` is only applicable to *output* streams. So, not only it isn't a "simple way to flush", it is actually a major error. – AnT stands with Russia Nov 23 '13 at 19:02
@AndreyT: Note that on some systems, `fflush(stdin)` is defined, notably on Windows and Linux (see [Using `fflush(stdin)`](http://stackoverflow.com/questions/2979209/using-fflushstdin)), but also on some other Unix-based systems. It is not defined behaviour according to the C standard or POSIX, but systems do define it. – Jonathan Leffler Feb 17 '14 at 15:26

scanf char variable in between scanf integer variable doesn't work?

3 Answers3