how to put index in string at the end code example

Example 1: python3 return a list of indexes of a specific character in a string

string='mississippi'
s='s'
lst= []
for i in range(len(string)):
    if (string[i] == s):
        lst.append(i)
print(lst)
#result: [2, 3, 5, 6]

Example 2: add char in specific index stirng javascript

int j = 123456;
String x = Integer.toString(j);
x = x.substring(0, 4) + "." + x.substring(4, x.length);

//output : 1234.56