View Compilation Error

0_0_38810922_27157.cpp: In function 'int sg(int, int)':
0_0_38810922_27157.cpp:3:3: error: 'sqrt' was not declared in this scope
    3 | = sqrt(s); while(t*t + t >= s) t--; if(c > t) return s - c;
      |   ^~~~
0_0_38810922_27157.cpp: In function 'int main()':
0_0_38810922_27157.cpp:5:6: error: expected ';' before ')' token
    5 | stdin); int n, c, s, cas = 0, flag; while(scanf("%d", &n), n){
      |      ^