Why is there an error of use of undeclared identifier in my selection sort function?

Question

I am trying to implement the selection sort function with the following code:

void sort(int values[], int n)
{
int temp;
for (int i = 0; i < n; i++)
{
    int min = i;
    for (int j = i+1; j < n; j++)
    {
        if (values[min] > values[j])
            min = j;
    }
    // Swap values;
    temp = values[min];
    values[j] = values[i];
    values[i] = temp;
}
}

I receive an error: helpers.c:40:16: error: use of undeclared identifier 'j' based on my use of

 values[j] = values[i];

I see that I can fix this by changing the j to min:

 values[min] = values[i];

However, I find this a little less clear. Why is there an error in the first way that I wrote it?

Answer 1

Where is j is declared?

for (int j = i+1; j < n; j++)

It can only be used within the code block ({.....}) where it is declared.