for 循环接受一个比循环条件额外的值

Question

I have written a program which accepts a value from a user and then iterates over that value in a for loop. in for loop I accept numbers to be stored in the array. My problem is for loop accepts one extra value than specified by user.

int main()
{
  int  i = 0;
  int  a;
  int no_of_boxcars = 0;
  double array[10];
  double boxcart_wt = 0;
  //printf("Enter the no of wagons");
  scanf_s("%d", &no_of_boxcars);        // no of boxcars
  for (i = 0; i<=no_of_boxcars;++i)
  {
    printf("%d \t", i);
    scanf_s("%lf ", &boxcart_wt);   //weight in boxcar

    array[i] = boxcart_wt;
  }
}

if the user enters 3 it should accept 3 values if

for (i = 0; i<no_of_boxcars;++i)
{
  //but here accepts 4 values
}

if the user enters 3 it should accept 4 values if

for (i = 0; i<=no_of_boxcars;++i)
{
  //and here accepts 5 values
}

Answer 1

Indexes in C go from 0..n-1 . In your for loop you go from 0..n and that is one too many. Change

for (i = 0; i<=no_of_boxcars;++i)

to

for (i = 0; i<no_of_boxcars;++i)

Answer 2

A space in the scanf format matches any white-space, and any number of consecutive white-space.

The problem with a trailing space is that then scanf must continue reading until it reads something that isn't a white-space, otherwise it doesn't know when the spaces ends.

That leads to the problem that you need to give some extra non white-space input.

For all but two formats ( "%c" and "%[" ) the scanf function automatically reads and discards leading white-space. So it's usually not needed to include spaces in a format string. Except perhaps for those two formats that doesn't skip white-space.

Read eg this scanf (and family) reference for more details.