gcc编译（Xcode工作，但unix不能）

Question

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int main(){
    double d;
    printf("Please input the smallest number : ");
    // Ask the user to enter the smallest number
    scanf("%le", &d);
    // save the value

    int n=1;
    int i=1;
    double pi=4/(2 * i - 1) * pow(-1,i + 1);
    double minvalue = 4/((2*(n+1))-1);
    // declare the values

    while(fabs(minvalue) >= d){
        // Using fabs() to return the absolute value
        minvalue = 4.0/((2*(n+1))-1);
        // useing the formula
        n++;
        // printf("%d",n);
    }

    int k = 2;
    for(; k <= n; k++){
        // we already calculate once before, so k = 2
        pi = pi + 4.0/(2 * k - 1) * pow(-1,k + 1);
    }

    printf("The value of pi is：%f\n",pi);

    return 0;

}

当我使用＆＃34; gcc -o main main.c＆＃34;在unix中发表评论，它出现了：

Undefined           first referenced
 symbol                 in file
pow                                 /var/tmp//ccaESiRZ.o
ld: fatal: symbol referencing errors. No output written to a.out
collect2: ld returned 1 exit status

任何解决方案？