formulla for calculate the occurance of a character in all substring of a given string .

Let's the length of the string is 'L' and index 'j' which is start from 0. the formulla is -
                       
                    occurance=(j+1)*(L-j);

ex:-
        let's string is "Rajnish" and we have to calculate occurancce of   'a' in all substring found by this string.then the program is-

#include<stdio.h>

#include<string.h>

void main()

{

char s[10];

int length,j,sum=0,fre=0;

scanf("%s",s);

length=strlen(s);

for(j=0;j<length;j++)

{

if(s[j]=='a')

{

sum=sum+(j+1)*(length-j);

fre++; // this is for how many times 'a' present in string because if 'a'

//found two times then two substring are same and we have to considered only one

}

}

printf("%d",sum-fre);

}