变量在声明它们之后具有值 [英] Variables have values after declaring them

问题描述

我刚开始学习c + +，我遇到了一个小问题。在声明变量后，他们将值分配给它们。

Im just starting to learn c++ and I've run into a little problem. After declaring variables they have value assigned to them.

#include <iostream>
#include <fstream>
using namespace std;

ifstream d ("d.txt");
ofstream r ("r.txt");

int plotas (int a, int b);

int main()
{
    int p,
        a,
        n,
        x1,
        x2,
        y1,
        y2,
        s,
        s1;
    d >> p >> a;
    d >> n;
    for(int i =0; i < n; i++){
        d >> x1 >> y1 >> x2 >> y2;
        s+= plotas((x2-x1), (y2-y1));
    }
    s1= plotas(p, a)- s;
    cout << s1;
}
int plotas (int a, int b){
    return a*b;
}

例如，变量s是1967866170。

For example variable s is 1967866170. Shouldn't they all be 0? What am I doing wrong?

推荐答案

未分配任何值的局部变量具有不确定值（也称为垃圾值，它是以前存储在该内存位置的值（在c和c ++中） ）和访问未初始化的变量会导致未定义的行为。

Local variables that are not assigned any values have what is called Indeterminate Value ( also known as Garbage Value, it is the value that was previously stored in that memory location ( in c and c++) ) and accessing uninitialized variables leads to Undefined Behavior.

如果你不给他们分配一个值，他们将有垃圾值。

If you do not assign them a value, they will be having the garbage value.

但 static 和全局变量的默认值为0

But static and global variables have default value as 0

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