c++ - Swap function based on ai+b mod n -

i need swap function swap based on results after computing ai+b mod n

for example have text : "test" , want swap based on ai+b mod n result ai+b mod n 2, 4, 1, 3 ie text after swap "etts" letter @ first position @ position 3, position 2 position 1, position 3 4 , 4 2.

the following code generate values ax+b mod n, need on how swap words in file. in advance.

int main () {     cout << "enter values of , b." << endl;     cin >> >> b;     cout << "enter input file name." << endl;     cin >> inputfile;      file * pfile;     pfile = fopen (inputfile, "rb");     if (pfile == null) perror ("error opening file");     else     {         fseek (pfile, 0, seek_end);   // non-portable         sizeoffile = ftell (pfile);         cout << sizeoffile << "\n";         fclose (pfile);     }      n = sizeoffile / 32;     cout << n << endl;      (i = 1; <= n; i++)     {         int message1 = ((a * + b) % n);         int c = message1;         cout << c << endl;     }     return c; } 

create second string, same length first, , copy (ai+b)'th character of first string i'th position of output.

keep in mind c++ starts counting @ 0.