Question

请帮助我，我的脑袋准备吹了

#include<stdio.h>
int main(void){
    unsigned short sum1=0;unsigned short counter=0;

    printf("Enter the number of integers you want to sum\n");scanf("%hd",&counter);
    for (unsigned int i=1;i<=counter;++i)
    { 
        printf("The i is %d and the sum is %d\n",i,sum1);
        sum1 =0;// 2 iteration sum =0;
        printf("The i is %d and the sum is %d\n",i,sum1);

        for(unsigned int j=1;j<=i;++j)
            sum1 =sum1+j;// 1 iteration sum=1;
        printf("The i is %d and the sum is %d\n\n",i,sum1);
    }
return 0;
}

到目前为止，我读过的书在嵌套循环中用于放置花括号但不在此例... 问题1）为什么在第二次迭代中总和将是3而不是2（我问这是因为sum在转到嵌套之前初始化为0）？问题2）为什么当我想printf（）j命中错误？任何人都可以解释我这个程序的工作原理吗？我的意思是第一次迭代，第二次迭代......谢谢兄弟......

Answer 1

此代码：

for (unsigned int i=1;i<=counter;++i)
{ printf("The i is %d and the sum is %d\n",i,sum1);
sum1 =0;// 2 iteration sum =0;
printf("The i is %d and the sum is %d\n",i,sum1);
for(unsigned int j=1;j<=i;++j)
sum1 =sum1+j;// 1 iteration sum=1;
printf("The i is %d and the sum is %d\n\n",i,sum1);}

相当于：

for (unsigned int i=1;i<=counter;++i) { 
    printf("The i is %d and the sum is %d\n",i,sum1);
    sum1 =0;// 2 iteration sum =0;
    printf("The i is %d and the sum is %d\n",i,sum1);
    for(unsigned int j=1;j<=i;++j) {
        sum1 =sum1+j;// 1 iteration sum=1;
    }
    printf("The i is %d and the sum is %d\n\n",i,sum1);
}

这是因为在没有大括号的for-loop中，只有下一行包含在循环中。

现在在第一次迭代中，您将得到：

"The i is 1 and the sum is 0"
"The i is 1 and the sum is 0"
"The i is 1 and the sum is 1" //Enters inner for-loop

第二

"The i is 2 and the sum is 1" //Hasn't reset yet
"The i is 2 and the sum is 0" //Reset
"The i is 2 and the sum is 3" //Sum was 0, then added 1 when j was 1, 
                              //then added 2 when j was 2

现在，您无法打印j的原因是因为您的printf语句都在您的内部for-loop之外，因此j未定义：）

Answer 2

在C语言中，您无法在for循环序列中声明变量：

for(int i=0; i<=10; i++)错了 int i;
for (i=0; i<=10; i++)是正确的

您也可以说int a,b,c=3;而不是单独声明int a, int b, int c=3;

为了帮助解决你的问题（我希望我可以评论，但我需要更多的声誉），如果你的声明（for，if，while）只有一个（或没有）操作，你不需要卷曲大括号：
for (i=0; i<=10; i++)
printf("%i ", i);

当进行更多操作时，你需要一个花括号来为compilator知道它们中有多少是在for循环中：

for (i=0; i<=10; i++){
printf("%i ", i);
if(i%2==1)
printf("Odd number");
printf("\n"); }

修改：
int i;
for(i=0; i<=10; i++){
int j = i+5; printf("%i", j); }
工作得非常好，但在for循环之外不能使用j。

没有花括号的嵌套循环

2 个答案: