c - 函数中未初始化的变量

Question

我的任务是编写一个接受三个输入并返回三个值的程序。整个程序在这里:

#include <stdio.h>


    int findPercent(int percent)
    {
    int p = percent / 100;
    return p;
    }

    double convertSquareYards(int a)
    {
    double sy = a * 4840;
    return sy;
    }

    double convertCubicYards(double sy, double i, int p)
    {
    double cy = (sy * p) * (i / 36);
    return cy;
    }

    double convertGallons(double cy)
    {
    double g = cy / 201.974026;
    return g;
    }

    double convertPounds(double g)
    {
    double lb = g / 8.3430;
    return lb;
    }

    double convertTonnes(double lb)
    {
    double t = lb / 2000;
    return t;
    }

    double convertCubicFeet(double cy)
    {
    double cf = cy * 27;
    return cf;
    }

    double findHeight(double cf)
    {
    double h = ((cf / (360 * 160)) / 5280);
    return h;
    }

    int main(void)
    {

    double g, t, h, lb, i, cy, a, percent, cf;

    printf("What is the size of the county in acres? ");
    scanf("%lf", &a);

    printf("How much rainfall was recieved, in inches? ");
    scanf("%lf", &i);

    printf("What percent of the county recieved rainfall? ");
    scanf("%lf", &percent);


    g = convertGallons(cy);
    t = convertTonnes(lb);
    h = findHeight(cf);

    printf("%lf gallons fell in the county.\n", g);
    printf("The rainfall weighed %lf tonnes.\n", t);
    printf("The height of the football field is %lf miles.\n", h);

    return 0;
    }

当我尝试编译该程序时，出现以下错误:

project.c:67:3: warning: ‘cy’ is used uninitialized in this function [-Wuninitialized]
g = convertGallons(cy);
  ^
project.c:68:3: warning: ‘lb’ is used uninitialized in this function [-Wuninitialized]
t = convertTonnes(lb);
  ^
project.c:69:3: warning: ‘cf’ is used uninitialized in this function [-Wuninitialized]
h = findHeight(cf);
  ^

我确信这个程序有很多问题(这是我的第一个真正的程序)，如果您愿意，我很乐意听到任何其他意见。先感谢您。

Answer 1

在这种情况下，警告非常具有描述性；您在初始化变量之前使用变量，这在 C 中不是一个好主意，例如

 g = convertGallons(cy);

cy 在上面使用之前没有初始化。使用

double cy = 0; // Or some other initial value

在声明期间(其他变量相同)。读取未初始化变量的值(这就是当该变量传递给函数时发生的情况 - 生成了它的副本，因此在某种程度上正在读取)是未定义的行为，并且编译器似乎是提示这一点。