View Compilation Error

0_0_30610839_2912.cpp: In function 'int calculate(char*, char*)':
0_0_30610839_2912.cpp:8:22: error: 'strlen' was not declared in this scope
     int len1=strlen(a);
                      ^
0_0_30610839_2912.cpp:10:29: error: 'memset' was not declared in this scope
     memset(a1, 0, sizeof(a1));
                             ^