在for循环中使用全局变量

for (int i = number_1; i > 0; i--)
{
    int j = 2;
    printf("%*s", i - 1,"");
    for (j; j > 0; j--)
    {
        printf("#");
    }
    printf("\n");
    j = j + 1;
}

Here I'm trying to run my secondary for loop by taking a variable that is declared in the previous loop. It iterates and prints the symbol "#", then gets incremented again by 1 before the outer loop ends.

在这里，我尝试使用前一个循环中声明的变量来运行第二个for循环。它迭代并打印符号“#”，然后在外部循环结束之前再增加1。

I'm getting this error:

我得到这个错误:

expression result unused

表达式结果未使用

What's going on here? I can certainly accomplish the task in a different way. But I'd like to find out why the code doesn't work in this case.

这是怎么回事?我当然可以用不同的方式完成任务。但是我想知道为什么在这种情况下代码不能工作。

3 个解决方案

#1

this statement:

这句话:

j = j + 1;

gives 'j' a value, but the next iteration through the loop hits this statement:

给'j'一个值，但循环的下一个迭代会遇到以下语句:

int j = 2;

So the results of the first statement are not used.

所以第一个语句的结果没有被使用。

However, since it is 'initialization', that might not matter.

但是，由于是“初始化”，这可能并不重要。

Then this statement:

然后这句话:

for (j; j > 0; j--)

has an error in the syntax. Where the first parameter is used to initialize a value, (in this case 'j') but no initialization is performed.

在语法中有错误。第一个参数用于初始化一个值(在本例中为'j')，但不执行初始化。

Suggest:

建议:

for (; j > 0; j--)

so the first parameter is omitted

因此省略了第一个参数

#2

change to

改变

for (int i = number_1, j = 2; i > 0; i--, ++j)//j move to this. 
{
    printf("%*s", i - 1,"");
    for (int k = j; k > 0; k--)
    {
        printf("#");
    }
    printf("\n");
}

#3

The error is usually only a warning. You have the expression j; here:

错误通常只是一个警告。有一个表达式j;在这里:

for (j; j > 0; j--)

but you don't assign the value of j to anything.

但是你没有把j的值赋给任何东西。

Change it to

将其更改为

for (; j > 0; j--)

And then there is another problem with j, as @user3629249 pointed out.
Move the declaration of j outside the loop:

还有另一个问题是j,@user3629249指出。移动j外循环的宣言:

int j = 2;
for (int i = number_1; i > 0; i--)
    {
        printf("%*s", i - 1,"");
        for (; j > 0; j--)
        {
            printf("#");
        }
        printf("\n");
        j = j + 1;
    }

#1