Question

    int ch;
    do
    {
            ch = getchar();
            printf("ch = %d\n",ch);
    }while(ch != '\n' && ch != EOF);

In this case the output for input 1234 is

    ch = 49
    ch = 50
    ch = 51
    ch = 52
    ch = 10

But on giving it like this

    char chs[100] = {0};
    unsigned int u = 0;
    int sign = 1,k=0;
    if(scanf("%[- 0-9]",&chs[0])== 1)
    {
             int ch;
             do
             {
              ch = getchar();
              printf("ch =  %d\n",ch);
             }while(ch != '\n' && ch != EOF);

In this case output for input = 1234 is

    ch =10

Why is this happening here ???
Can someone please explain … Why isn’t the output same as before ??

How scanf is exactly working here ?

Answer 1

The call to scanf reads data from the stream. When you later try to read from the stream again by using getchar the characters that were read by scanf have already been consumed and are not read again.

Also, see the documentation for scanf for valid values of the format string.