c - 即使在代码的前面声明了变量，也会出现“未声明的标识符”错误

Question

当用户输入值时，

int 变量 h 在第 10 行声明。

但是，当代码编译时，它说它是未声明的。

#include <cs50.h>
#include <stdio.h>

int main(void)
{
    printf("How tall would you like your pyramid?\n");
    bool inc = true;
    while (inc)
    {
        int h = GetInt();
        if (h <= 23 && h >= 1)
        {
            inc = false;
        }
        else
        {
            printf("your value needs to be between 1 and 26\n");
        }
    }

    for (int i=0; i<=h; i++)
    {
        printf("#\n");
    }
}

Answer 1

你的变量h在另一个城堡里:

while (inc)
{
    int h = GetInt();
    if (h <= 23 && h >= 1)
    {
        inc = false;
    }
    else
    {
        printf("your value needs to be between 1 and 26\n");
    }
    // h is destroyed after this line and is no longer visible.
}

for (int i=0; i<=h; i++)
{
    printf("#\n");
}

括号表示范围，范围表示变量可见性。 h 在 while 循环的范围内声明，h 在该范围之外不可见，在 之外也不可见}循环的。如果你想在循环之外访问它，你应该把它放在循环之外:

int h = -1;
while (inc)
{
    h = GetInt();
    if (h <= 23 && h >= 1)
    {
        inc = false;
    }
    else
    {
        printf("your value needs to be between 1 and 26\n");
    }
}

for (int i=0; i<=h; i++)
{
    printf("#\n");
}
// h is still visible here.