View Compilation Error

0_0_14744999_25500.cpp: In function 'int main()':
0_0_14744999_25500.cpp:13:19: error: 'strcpy' was not declared in this scope
    strcpy(t[num],x);
                   ^
0_0_14744999_25500.cpp:14:16: error: 'strlen' was not declared in this scope
    len=strlen(x);
                ^
0_0_14744999_25500.cpp:17:17: error: 'strcmp' was not declared in this scope
    if(strcmp(x,y)==0) break;                           //不相等 
                 ^