a c programming question

all. I am not sure whether it is appropriate to ask such a 'simple' question here, but actually it's hard for me :[ , and here is the question and a bit of c code:

main()
{
    int c, i;
    for (i = 0; (c = getchar()) != EOF && c != '\n'; ++i)
        printf("%d", i);
    if (c == '\n')
        printf("%d", i);
}
开发者_JAVA百科

After executing this program, when I input, say, "abc\n", the program will return:

0
1
2
3

I wondered why the result is not

0
1
2

since when c == '\n', there are no statement that increments i by 1. This is what I thought, I must be wrong, would you tell me where I was wrong? Thanks!

The sequence of operations in the for loop are:

i = 0
(c = getchar()) != EOF && c != '\n' // c is set to 'a'
printf("%d", i)    // displays 0

++i   // i == 1
(c = getchar()) != EOF && c != '\n' // c is set to 'b'
printf("%d", i)    // displays 1

++i   // i == 2
(c = getchar()) != EOF && c != '\n' // c is set to 'c'
printf("%d", i)    // displays 2

++i   // i == 3
(c = getchar()) != EOF && c != '\n' // c is set to '\n'
// the loop exits

So the printf() that's after the for loop prints the most recent value for i, which is 3.

The ++i gets executed after the c == '\n' case.

Perhaps this code would help clarify?

int i;
for (i = 0; i <= 3; ++i)
    printf("%d\n", i);

At the end of the loop, i will be 4, because of that final increment.

The main problem is with pre increment of index variable i. In stead of pre increment, use post increment i.e. i++ inside the for loop.The reason behind that is due to pre increment. When the condition inside the loop halts, the value stored in i is already 4 when you use pre increment.

main()
{
    int c, i;
    for (i = 0; (c = getchar()) != EOF && c != '\n'; i++)
        printf("%d", i);
    if (c == '\n')
        printf("%d", i);
}