小编use*_*546的帖子

我在理解指针时遇到了一些麻烦.在下面的代码中,我尝试以两种方式打印变量的地址 - 一次使用地址运算符然后使用指针:

#include<iostream>
using namespace std;
int main (void)
{
    int x = 10;
    int *int_pointer;
    int_pointer = &x;
    cout << "x address=" << &x << endl;
    cout << "x address w pointer=" << int_pointer << endl;
    return 0;
}

x address = 0028FCC4
x address w pointer = 0028FCC4

这按预期工作.但是,当我做同样的事情,但现在使用字符类型变量,我得到一些垃圾输出:

#include<iostream>
using namespace std;
int main(void)
{
    char c = 'Q';
    char *char_pointer;
    char_pointer = &c;
    cout << "address using address operator=" << &c << endl;
    cout << …

我想补充标题"1999年至2008年美国PM2.5的排放",该标题使用r中的基础绘图功能.在那,我希望2.5成为PM的下标.如果PM2.5恰好位于字符串的末尾,我没有任何问题:

barplot(height = total.emissions$Emissions, names.arg=total.emissions$year,  
        xlab="Year", ylab= " Amount of emitted in tonsPM"2.5 ,   
        main = "Emissions from in the United States from 1999 to 2008PM"[2.5] )

但如果它在字符串的中间,我就不能这样做.如果我把它分成两部分,如下:

barplot(height = total.emissions$Emissions, names.arg=total.emissions$year,  
        xlab="Year", ylab= " Amount of PM_[2.5] emitted in tons",   
        main = expression("Emissions from PM"[2.5] "in the United States from 1999 to 2008"))

由于方括号,我收到错误说出意外的符号.