Inserting characters at specified position

Question

I want to make a program that when the user enters AB1245 and have the program change it to AB 12345 (an added space between 2nd and 3rd character)

char Bilnr[9];

for (i = 8; i < 3; i--) {
    Bilnr[i++]=Bilnr[i];

}

As I understand this, this program will start with Bilnr[9] and set it to the value of Bilnr[8].

Then set Bilnr[8] to the value of Bilnr[7].

But it doesn't move any of the values. It simply prints AB1245.

Answer 1

One thing I notice is that if your loop ever actually executes, it would be infinite

for (I=8; I<3; I--) {
    Bilnr[I++]=Bilnr[I];

}

I++ doesn't mean I+1 rather, it means I = I+1

but your loop won't execute, because your condition, I<3 will be false from the get-go when you initialize I with I=8

You're also never setting I[2] to be a ' '

you also also have to realize that arrays start at 0, so Bilnr[0] == 'A'

try

for(int i = 8; i > 2; i--)
{
    Bilnr[i] = Bilnr[i-1];
}
Bilnr[2] = ' ';

Answer 2

It prints the same, because the loop never runs. The loop condition is wrong, it should be I>3 to start. The for loop works as follows:

for (initialization; condition-that-has-to-be-true; optional-increment-decrement) {
}

Also remember C/C++ arrays start counting at 0, not 1.

To fix your complete code:

char Bilnr[9] = "AB12345";

for (I=7; I>2; I--) {
    Bilnr[I]=Bilnr[I-1];
}

Then you have AB112345. All you need then is put in the space:

Bilnr[2] = ' ';