How to find Count of chararter in String

Query to get the count of I's present in the string:

To find Count of charater in string we need to check length of string - length of string without that charater. For example We need to find Count of I in "This is the string where I need to count number of I are present in line", means Check the lengh of "This is the string where I need to count number of I are present in line" - check length of "Ths s the strng where need to count number of are present n lne"