读取一定量的水，以夸脱为单位，并显示该数量的水分子数。

单分子水的质量约为3.0×10克。一夸脱水约950克。

#include <stdio.h>  

int main(void)  
{  
    float mass_mol = 3.0e-23;    /* mass of water molecule in grams */  
    float mass_qt = 950;        /* mass of quart of water in grams */  
    float quarts;  
    float molecules;  

    printf("Enter the number of quarts of water: ");  
    scanf("%f", &quarts);  
    molecules = quarts * mass_qt / mass_mol;  
    printf("%f quarts of water contain %e molecules./n", quarts, molecules);  
    return 0;  
}