View Compilation Error

0_0_19571783_20532.cpp: In function 'void build(char*)':
0_0_19571783_20532.cpp:13:21: error: 'strlen' was not declared in this scope
   int len=strlen(str);
                     ^
0_0_19571783_20532.cpp: In function 'int find(char*)':
0_0_19571783_20532.cpp:37:21: error: 'strlen' was not declared in this scope
   int len=strlen(str);
                     ^
0_0_19571783_20532.cpp: In function 'int main()':
0_0_19571783_20532.cpp:60:21: error: 'strcmp' was not declared in this scope
     if(strcmp(str,"")==0)
                     ^