01  #include <math.h>
02  #include <stdio.h>
03  
04  int main()
05  {
06    double result;
07    double x = 8.6872;
08  
09    result = log(x);
10    printf("The natural log of %lf is %lfn", x, result);
11  
12    return 0;
13  }

 OUTPUT :
 
 The natural log of 8.687200 is 2.161851