KMP prefix table

Question

I am reading about KMP for string matching.
It needs a preprocessing of the pattern by building a prefix table.
For example for the string ababaca

Answer 1

string text = "ababbabbababbababbabb"; static int arr[30];

int i = 1;
while (i < text.length())
{
    int j = 0;
    int value = 0;
    while (((i + j) < text.length()) && (text[j] == text[i + j]))
        val[i + j] = ++value, j++;
    i += j + 1;
}

required output stored in val[]