View Compilation Error

0_0_31868266_30714.cpp: In function 'int main()':
0_0_31868266_30714.cpp:9:14: error: 'strlen' was not declared in this scope
   k1=strlen(a);
              ^
0_0_31868266_30714.cpp:13:16: error: 'strstr' was not declared in this scope
   if(strstr(a,b)) printf("yes\n");
                ^