scanf in switch case C programming

Question

Here is my code:

#include <stdio.h>

int main() {
    char op;
    int num1, num2;
    printf("Enter the operation(+,-,/,*,!,^) :  ");
    scanf(" %c", &op);
    switch (op) {
      case '+':
        printf("Enter the first operand : ");
        scanf(" %d", num1);
        printf("Enter the second operand : ");
        scanf(" %d", num2);  
        printf("%d", num1 + num2);
        break;
    }
}

when I run this. code stops after me entering first operand. I added space before scanf but it didn't solve the problem below.

output of code

Don't post pictures of text. Post text as text. Output is text. — Jabberwocky, Mar 28 '23 at 14:43
You'll need to discard the trailing line feed character from stdin. But that's not the only problem, you have some basic syntax errors `scanf(" %d",num1);` which the compiler should already have told you about: [What compiler options are recommended for beginners learning C?](https://software.codidact.com/posts/282565) — Lundin, Mar 28 '23 at 14:44
Somewhat unrelated: your approach is somewhat wrong. Write the code for the `-` operator and you'll understand what I mean. — Jabberwocky, Mar 28 '23 at 14:47
@Jabberwocky There's several problems here. Though I don't know a dupe for "basic scanf syntax errors made by every beginner". Maybe this one is better: https://stackoverflow.com/questions/35178520/how-to-read-parse-input-in-c-the-faq — Lundin, Mar 28 '23 at 14:48
@Lundin I'mean with the space in front of the scanf conversion specifiers (which the OP has put in their code) it should work provided the `&` is added. The real problem is the missing `&` which the dupe does not address. — Jabberwocky, Mar 28 '23 at 14:52
Note that you can take input before the switch statement. That way, you won't have to write the same code for every operator. — Harith, Mar 28 '23 at 15:03
You only need the space before the conversion specifications which don't automatically skip white space — and there are only three of those: `%c`, `%[…]` (scan sets) and `%n`. All the other conversion specifications skip white space automatically, whether you want them to or not. And white space includes newlines, of course. The `scanf()` function basically doesn't care about newlines — essentially, it can't be used reliably where you need line-based input. Use `fgets()` or POSIX `getline()` to read a line, and then use `sscanf()` or other functions to parse the line that was read. — Jonathan Leffler, Mar 28 '23 at 22:06

Jabberwocky · Accepted Answer · 2023-03-28T20:40:00.527

2

You forgot to add the address operator (&) in front of the num1 and num2 variables in the calls to scanf.

Modify those two lines like this:

scanf(" %d", &num1);
scanf(" %d", &num2);
//           ^add the &

edited Mar 28 '23 at 20:40

answered Mar 28 '23 at 14:56

Jabberwocky

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score -1 · Answer 2 · edited Apr 02 '23 at 03:04

-1

I usually add an & after the comma of every scanf I mean really when your advancing and that mistake is not corrected it can be annoying:

scanf("%d", &var);

edited Apr 02 '23 at 03:04

user16217248

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answered Apr 01 '23 at 15:18

mr. code

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*"I usually add an & after the comma of every scanf"* Do you understand what function `&` even has? – gre_gor Apr 29 '23 at 18:42

scanf in switch case C programming

2 Answers2