C/C++ printf() before scanf() issue

Question

I'm using Eclipse to code in C/C++ and I'm struggling with what might be something pretty easy. In my code below I use printf() and after scanf(). Althougth printf is written before scanf() the output differs. I was able to find out something about similar issue here. But I wasn't able to solve it. Any ideas?

Code:

#include <stdio.h>

int main()
{
    int myvariable;

    printf("Enter a number:");
    scanf("%d", &myvariable);
    printf("%d", myvariable);

    return 0;
}

Expected output:

Enter a number:1
1

Instead I get:

1
Enter a number:1

Solution 1

Your output is being buffered. You have 4 options:

1. explicit flush

   fflush after each write to profit from the buffer and still enforce the desiredbehavior/display explicitly.

    fflush( stdout );
   

2. have the buffer only buffer lines-wise

   useful for when you know that it is enough to print only complete lines

    setlinebuf(stdout);
   

3. disable the buffer

    setbuf(stdout, NULL);
   

4. disable buffering in your console through what ever options menu it provides

---

Examples:

Here is your code with option 1:

#include <stdio.h>
int main() {

    int myvariable;
    
    printf("Enter a number:");
    fflush( stdout );
    scanf("%d", &myvariable);
    printf("%d", myvariable);
    fflush( stdout );

    return 0;
}

---

Here is 2:

#include <stdio.h>
int main() {

    int myvariable;

    setlinebuf(stdout);    

    printf("Enter a number:");
    scanf("%d", &myvariable);
    printf("%d", myvariable);

    return 0;
}

---

and 3:

#include <stdio.h>
int main() {

    int myvariable;

    setbuf(stdout, NULL);     

    printf("Enter a number:");
    scanf("%d", &myvariable);
    printf("%d", myvariable);

    return 0;
}

Solution 2

Ok, so finally I used something similar to what @zsawyer wrote as an option labelled 3. In my code I inserted this line:

setvbuf(stdout, NULL, _IONBF, 0);

As a first line in main():

#include <stdio.h>

int main()
{
    setvbuf(stdout, NULL, _IONBF, 0);

    int myvariable;

    printf("Enter a number:");
    scanf("%d", &myvariable);
    printf("%d", myvariable);

    return 0;
}

I got it from here.