函数名: log10 
 功  能: 对数函数log 
 用  法: #include <math.h> 
         double log10(double x); 
 程序例: 
#include <math.h> 
 #include <stdio.h> 
int main(void) 
 { 
    double result; 
    double x = 800.6872; 
   result = log10(x); 
    printf("The common log of %lf is %lf\n", x, result); 
   return 0; 
 }