View Compilation Error

0_0_29278719_13642.cpp: In function 'int main()':
0_0_29278719_13642.cpp:11:18: error: 'strlen' was not declared in this scope
   if (strlen(a[i]) < strlen(b[i])) {
                  ^
0_0_29278719_13642.cpp:13:18: error: 'strcpy' was not declared in this scope
    strcpy(t, a[i]);
                  ^
0_0_29278719_13642.cpp:18:22: error: 'strlen' was not declared in this scope
   int n = strlen(a[i]) - strlen(b[i]);
                      ^
0_0_29278719_13642.cpp:22:17: error: 'strcat' was not declared in this scope
   strcat(t, b[i]);
                 ^
0_0_29278719_13642.cpp:23:20: error: 'strcpy' was not declared in this scope
   strcpy(s[i], a[i]);
                    ^