c - 没有花括号的嵌套循环

Question

请帮帮我，我的头要炸了

#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;
}

直到现在我读的书在嵌套循环中用来放置花括号但不是在这个例子...问题 1)为什么在第二次迭代中总和将是 3 而不是 2(我问这个是因为总和在转到嵌套 for 之前初始化为 0)？问题 2)为什么当我想 printf() 时 j 会出错？任何人都可以向我解释这个程序是如何工作的吗？我的意思是第一次迭代，第二次迭代....谢谢兄弟....

Answer 1

这段代码:

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，只有下一行被包含在循环中。

现在在第一次迭代中，您将获得:

"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

第二个:

"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，你不能打印 j 的原因是因为你的 printf 语句都在你内部的 for-loop 之外，所以 j 未定义:)