View Compilation Error

0_0_38684423_16242.cpp: In function 'i64 fpow(i64, i64)':
0_0_38684423_16242.cpp:11:5: error: 'a' was not declared in this scope
   11 |     a = (a + mod) % mod;
      |     ^
0_0_38684423_16242.cpp:12:12: error: 'b' was not declared in this scope
   12 |     while (b)
      |            ^