View Compilation Error

0_0_23186257_10068.cpp: In function 'int main()':
0_0_23186257_10068.cpp:2:227: error: 'pow' was not declared in this scope
 main() {      double m,n,i,s,j,k,a;      while(scanf("%lf",&m)!=EOF)     {           for(i=0;i<m;i++)         {              s=0;              scanf("%lf",&n);             for(j=1;j<=n;j++)                   s=s+1/j*pow(-1,j+1);               printf("%.2lf\n",s);         }       } }
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