运行循环或者整段代码​的时候报错“未定义函​数或变量”，但单独执​行该段代码会将添加路​径的数据赋值给变量，​并且相同路径的上一个​变量的赋值就正常

data_num=1;
for num1=1:data_num
    switch num1
        case  1
            s4='F:\data\sourc1.txt';
            sou4=load(strcat(s4));
            pd1_1=sou4(1:2:end,:);
            pd2_1=sou4(2:2:end,:);
        case  2
            s5='F:\data\source1.txt';
            sou5=load(strcat(s5));
            pd1_2=sou5(1:2:end,:);
            pd2_2=sou5(2:2:end,:);
        otherwise
            disp('input data error')
    end

NOTE: 只截取了程序的出错部分，无法在网站运行，还请各位论坛大神帮忙解答debug

报错：未定义函数或变量‘pd1_2'

Answer 1

[Sugandhi]

Hi Jiamin Ji,

The error you're encountering, "Undefined function or variable 'pd1_2'", occurs because the `case 2` block is never executed. This is due to the fact that the loop only runs once (`data_num = 1`), and thus, the `switch` statement only evaluates `case 1`. As a result, `pd1_2` and `pd2_2` are never defined. Possible workarounds:

1. If you intend to execute both cases, increase the `data_num` to at least 2.
2. If `case 2` might not always execute, initialize `pd1_2` and `pd2_2` outside the loop to avoid the undefined variable error.
3. Before accessing `pd1_2` and `pd2_2`, add a check to ensure they are defined.

[Jiamin Ji]

Thanks very much for your so kind and patient answer, I have already solved it.

Answer 2

[jinjin lee]

很明显你那个switch是根据你的num1的值执行的，num1=1是只有pd1_1和pd2_1有值， pd1_2和 pd2_2均没有赋值也没有这两个变量，那么你后面的代码如果引用pd1_2和 pd2_2，那必然报错啊。

[Jiamin Ji]

是的，已解决。感谢坛友友善耐心指出粗心小问题