scanf() doesn't execute in its 2nd time use

[dnayak382]

i am a beginner to c programming language...

can anyone plz explain "why scanf() statement is not working after its use in the condition part of the while loop" as in the code is in attachment.

#include <stdio.h>

int main()
{
    int n[50], num;
    int i = 0, c = 0;

    printf("Enter numbers (At end enter any letter): ");
    while (scanf("%d", &n[i]))
    {
        i++;
    }

    printf("\n\tEnter a number: ");
    scanf("%d", &num);          //This statement doesn't execute

    printf("\n\tnum = %d", num);

    return 0;
}

[Salem]

Well if you entered
1 2 3 a
to make the first loop end, then the "a" will still be there, ready to fail on the next scanf as well.

You need to remove the unwanted data from the input stream before trying to read another int.

[mcpaddington]

I'm also a beginner to C, but from what I see you just need to put in a fflush. Here is a revised piece of code I made. I'm not entirely sure what your programs first line does or why a letter needs to be answered but here you go.

#include <stdio.h>

int main()
{
    int n[50], num;
    int i = 0, c = 0;

    printf("Enter numbers (At end enter any letter): ");
    while (scanf("%d", &n[i]))
    {
        i++;
    }

    printf("\n\tEnter a number: ");
    fflush(stdin);
    
    scanf("%d", &num);          //This statement doesn't execute

    printf("\n\tnum = %d", num);
    fflush(stdin);
    getchar();
}

[tabstop]

Cprogramming.com FAQ > Why fflush(stdin) is wrong

[mcpaddington]

Ok after reading a FAQ about it, I found away around it. Can someone please explain how this works and if it is "acceptable" to use it ?

#include <stdio.h>


 void myflush ( FILE *in )
{
  int ch;

  do
    ch = fgetc ( in ); 
  while ( ch != EOF && ch != '\n' ); 

  clearerr ( in );
}

void mypause ( void ) 
{ 
  fflush ( stdout );
  getchar();
}

int main( void )
{
    int n[50], num;
    int i = 0, c = 0;

    printf("Enter numbers (At end enter any letter): ");
    while (scanf("%d", &n[i]))
    {
        i++;
    }

    printf("\n\tEnter a number: ");
    myflush ( stdin );
    scanf("%d", &num);          //This statement doesn't execute
    
    printf("\n\tnum = %d", num);
    myflush ( stdin );
    mypause();
}

[AndrewHunter]

Ok after reading a FAQ about it, I found away around it. Can someone please explain how this works and if it is "acceptable" to use it ?

This was recently discussed in this thread. Take a look through there and then ask if you have any additional questions.

[mcpaddington]

This was recently discussed in this thread. Take a look through there and then ask if you have any additional questions.

Ok I get most of it now, just one question. What does 'EOF' stand for ?

Edit: Nevermind I think I found it, does it mean End of File ?

[AndrewHunter]

End of File flag, it gets set when no more input can be read from a stream(which does include keyboard input). EOF - Wiki

[mcpaddington]

End of File flag, it gets set when no more input can be read from a stream(which does include keyboard input). EOF - Wiki

Thank you for your help