View Compilation Error

0_0_21232961_10167.cpp: In function 'int main()':
0_0_21232961_10167.cpp:8:18: error: 'strcmp' was not declared in this scope
   if(strcmp(s,"0")==0)
                  ^
0_0_21232961_10167.cpp:10:19: error: 'strlen' was not declared in this scope
   int len=strlen(s),n=0;
                   ^
0_0_21232961_10167.cpp:13:4: error: 'n' was not declared in this scope
    n=n+s[i]-'0';
    ^
0_0_21232961_10167.cpp:15:6: error: 'n' was not declared in this scope
   if(n>9)
      ^
0_0_21232961_10167.cpp:17:6: error: 'n' was not declared in this scope
   if(n==0)
      ^