/in/foo.cc: In function 'void f(int)':
/in/foo.cc:17:9: warning: unused variable 'c' [-Wunused-variable]
    char c = s[i];
         ^
/in/foo.cc:46:9: warning: unused variable 'c' [-Wunused-variable]
    char c = s[i];
         ^
/in/foo.cc:76:9: error: redeclaration of 'char ch'
    char ch = s[i+1];
         ^~
/in/foo.cc:75:9: note: 'char ch' previously declared here
    char ch = s[i];
         ^~
/in/foo.cc:75:9: warning: unused variable 'ch' [-Wunused-variable]