View Compilation Error

0_0_13941304_6739.cpp: In function 'void dp(int)':
0_0_13941304_6739.cpp:35:11: error: 'a' was not declared in this scope
         f[a[i]] = max + 1;
           ^
0_0_13941304_6739.cpp: In function 'int main()':
0_0_13941304_6739.cpp:59:13: error: 'a' was not declared in this scope
             a[i] = str[i] - 'a' + 1;
             ^