View Compilation Error

0_0_18616316_22432.cpp: In function 'int main()':
0_0_18616316_22432.cpp:13:10: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    if(a>='0'&&a<='9') sum+=1;
          ^
0_0_18616316_22432.cpp:13:18: error: ISO C++ forbids comparison between pointer and integer [-fpermissive]
    if(a>='0'&&a<='9') sum+=1;
                  ^