vector subscription out of range c++ - c++

Question

I am working on a program that reads integers from file, stores it in vector and use count sort to sort the integers and write them in new file. My problem ocurs when i run Countsort function, the breakpoint happens at this for loop:
for (int i = 0; i < C.size(); i++) {
C[A[i]] = C[A[i]] + 1;
}
my code looks like this:
//COUNT SORT
void countsort() {
int max = A[0];
for (int i = 1; i < A.size(); i++) {
if (A[i] > max) {
max = A[i];
}
}
//cout << "NAJVECJE STEVILO JE: " << max << endl; SAMO ZA TEST
vector<int> C(max + 1);
vector<int> B(A.size());
for (int i = 0; i < C.size(); i++) {
C[A[i]] = C[A[i]] + 1;
}
for (int i = 1; i < C.size(); i++) {
C[i] = C[i] + C[i + 1];
}
for (int i = C.size() - 1; i >= 0; i--) {
B[C[A[i]] - 1] = A[i];
C[A[i]] = C[A[i]] - 1;
}
for (int i = 0; i < A.size(); i++) {
A[i] = B[i];
}
}

Answer 1

First you zero whole C vector
for (int i = 0; i < C.size(); i++)
{
C[i] = 0;
}
In second loop you may not change C[0] so it will remain 0
for (int i = 0; i < A.size(); i++)
{
C[A[i]] = C[A[i]] + 1;
}
In third loop in my analysis you never change C[0]
for (int i = C.size() - 1; i > 0; i-- )
{
C[i] = C[i] + C[i - 1];
}
In last loop
for (int i = A.size() - 1; i >= 0; i--)
{
B[C[A[i]] - 1] = A[i];
C[A[i]] = C[A[i]] - 1;
cout << B[i] << " ";
}
A[i] may equal 0, so C[A[i]] is C[0] and it might equal 0 from analysis of previous loops. When you subtract 1 from it, you'll end up with B[-1] which breaks your code.

Answer 2

Before you write something to B vector you should probably initialize it firt like you did with C.
B = vector<int>(A.size());
Also I don't see any point of printing B[i] as it may not be assigned any value when you print it.
Edit #1
Your loop is not correct. Take a look at this:
for (int i = 1; i < C.size(); i++) {
C[i] = C[i] + C[i - 1];
}
Edit #2
Try this code.
vector<int> A, B;
//COUNT SORT
void countsort() {
int max = A[0];
for (int i = 1; i < A.size(); i++) {
if (A[i] > max) {
max = A[i];
}
}
vector<int> C(max + 1);
B = vector<int>(A.size());
for (int i = 0; i < C.size(); i++) C[i] = 0;
for (int i = 0; i < A.size(); i++) C[A[i]] = C[A[i]] + 1;
for (int i = 1; i < C.size(); i++) C[i] = C[i] + C[i - 1];
for (int i = A.size() - 1; i >= 0; i--) {
B[C[A[i]] - 1] = A[i];
C[A[i]] = C[A[i]] - 1;
}
for (int i = 0; i < B.size(); i++) cout << B[i];
}
int main(void) {
A.push_back(1);
A.push_back(2);
A.push_back(3);
A.push_back(4);
A.push_back(2);
A.push_back(2);
A.push_back(1);
countsort();
}