View Compilation Error

0_0_37359734_22704.cpp: In function 'int main()':
0_0_37359734_22704.cpp:7:18: error: 'a' was not declared in this scope
             gets(a);
                  ^
0_0_37359734_22704.cpp:10:15: error: 'b' was not declared in this scope
               b[sum]=a[0];
               ^
0_0_37359734_22704.cpp:16:14: error: 'b' was not declared in this scope
              b[sum]=a[0];
              ^
0_0_37359734_22704.cpp:24:18: error: 'b' was not declared in this scope
                  b[sum]=a[i+1];
                  ^
0_0_37359734_22704.cpp:30:17: error: 'b' was not declared in this scope
                 b[sum]=a[i+1];
                 ^
0_0_37359734_22704.cpp:35:25: error: 'b' was not declared in this scope
             printf("%s",b);
                         ^
0_0_37359734_22704.cpp: At global scope:
0_0_37359734_22704.cpp:39:14: error: expected unqualified-id before 'return'
              return 0;
              ^
0_0_37359734_22704.cpp:40:14: error: expected declaration before '}' token
              }
              ^