scanf "extra input" required

Question

for some simple HW code I wrote I needed to get 7 arguments via the scanf function:

scanf("%d %d %d %d\n", &vodka, &country, &life, &glut);
scanf("%d\n", &ageof);
scanf("%d\n", &dprice);
scanf("%d\n", &mprice);

as you can see, I'm asking for 7 arguments in this order:

argument [space] argument [space] argument [space] argument (down line)

argument (down line)

argument (down line)

argument (down line)

BUT, when running the code, I'm suddenly required to input 8 of them, and I have no idea why....

any help anyone?

Answer 1

As explained by @chqrlie and @Blue Moon a white space in the format, be it ' ', '\n', '\n' or any white-space does the same thing. It directs scanf() to consume white-space, such as '\n' from an Enter, until non-white-space is detected. That non-white-space character is then put back into stdin for the next input operation.

scanf("%d\n", ...) does not return until some non-white space is entered after the int. Hence the need for the 8th input. That 8th input is not consumed, but available for subsequent input.

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The best way to read the 4 lines of input is to .... drum roll ... read 4 lines. Then process the inputs.

char buf[4][80];
for (int i=0; i<4; i++) {
  if (fgets(buf[i], sizeof buf[i], stdin) == NULL) return Fail;
}
if (sscanf(buf[0], "%d%d%d%d", &vodka, &country, &life, &glut) != 4) {
  return Fail;
}
if (sscanf(buf[1], "%d", &ageof) != 1) {
  return Fail;
}
if (sscanf(buf[2], "%d", &dprice) != 1) {
  return Fail;
}
if (sscanf(buf[3], "%d", &mprice) != 1) {
  return Fail;
}
// Use vodka, country, life, glut, ageof, dprice, mprice
return Success