View Compilation Error

0_0_36579079_25713.cpp: In function 'int main()':
0_0_36579079_25713.cpp:26:16: error: 'strlen' was not declared in this scope
    len=strlen(s);
                ^
0_0_36579079_25713.cpp:41:39: error: 'strcmp' was not declared in this scope
     if(strcmp(dic[i].back,dic[j].front)==0)
                                       ^