当float包含等式时,得到0作为结果

Question

我正在尝试编写一个非常简单的程序,将几夸脱的水(用户输入)转换为C中的水分子.

#include <stdio.h>
#include <float.h>

int main(void)
{
    float water_quarts;
    float water_grams = (water_quarts*950.00);
    float water_molecules = (water_grams/3e-23F);


    printf("Enter an amount of water in quarts: \n");
    scanf("%f", &water_quarts );
    printf("%f quarts is %f grams of water.\n", water_quarts, water_grams );
    printf("%f grams is %f molecules of water.\n", water_grams, water_molecules );

    return 0;
}

但是,当我编译并运行它时,它给了我:

Enter an amount of water in quarts: 
15
15.000000 quarts is 0.000000 grams of water.
0.000000 grams is 0.000000 molecules of water.

我不完全确定我做错了什么.我在lubuntu 14.10上使用gcc 4.9.1,通过VirtualBox运行.

Answer 1

您需要将值分配给water_grams和water_molecules你把输入后water_quarts从用户(也就是你以后scanf()).

#include <stdio.h>
#include <float.h>

int main(void)
{
    float water_quarts;
    printf("Enter an amount of water in quarts: \n");
    scanf("%f", &water_quarts );

    float water_grams = (water_quarts*950.00);
    float water_molecules = (water_grams/3e-23F);

    printf("%f quarts is %f grams of water.\n", water_quarts, water_grams );
    printf("%f grams is %f molecules of water.\n", water_grams, water_molecules );

    return 0;
}

或者

float water_quarts;
float water_grams ;
float water_molecules ;


printf("Enter an amount of water in quarts: \n");
scanf("%f", &water_quarts );
water_grams  = (water_quarts*950.00);
water_molecules  = (water_grams/3e-23F);

否则,您要为它们分配未初始化的值,这就是您获得意外输出的原因.

当你声明一个变量时,它会有一些垃圾值(除非你为它赋值一些),并且由于这个原因,当你做

float water_grams = (water_quarts*950.00);
float water_molecules = (water_grams/3e-23F);

water_quarts 有一些垃圾值,因此,你只是给其他变量分配一些垃圾.