[英]Need help understanding this C Code (Array)
我需要帮助才能清楚地理解这段代码,请帮忙。 我无法弄清楚该程序如何跟踪响应数组中给出了多少个数字。 我不明白 for 循环发生了什么,特别是这条线 ++frequency[responses[answer]];
#include<stdio.h>
#define RESPONSE_SIZE 40
#define FREQUENCY_SIZE 11
int main(void)
{
int answer; /* counter to loop through 40 responses */
int rating; /* counter to loop through frequencies 1-10 */
/* initialize frequency counters to 0 */
int frequency[FREQUENCY_SIZE] = {0};
/* place the survey responses in the responses array */
int responses[RESPONSE_SIZE] = {1,2,6,4,8,5,9,7,8,10,1,6,3,8,6,10,3,8,2,7,6,5,7,6,8,6,7,5,6,6,5,6,7,5,6,4,8,6,8,10};
/* for each answer, select value of an element of array responses
and use that value as subscript in array frequency to determine element to increment */
for(answer = 0 ; answer < RESPONSE_SIZE; answer++){
++frequency[responses[answer]];
}
printf("%s%17s\n", "Rating", "Frequency");
/* output the frequencies in a tabular format */
for(rating = 1; rating < FREQUENCY_SIZE; rating++){
printf("%6d%17d\n", rating, frequency[rating]);
}
return 0;
}
for(answer = 0 ; answer < RESPONSE_SIZE; answer++){
++frequency[responses[answer]]; // <---
}
上面的循环只计算一个数字出现在数组responses
的次数,并存储在数组frequency
中该数字的索引处。 此行在第一个循环中执行此操作 -
++frequency[responses[answer]];
因此,它在数组frequency
索引responses[answer]
处增加值。
假设responses[answer]
值为1
,然后数组frequency
索引1
的值递增。
如前所述,第二个for
循环仅用于输出。
++frequency[responses[answer]]
是一种密集的写作方式
int r = response[answer];
frequency[r] = frequency[r] + 1;
需要注意的是frequency[r]
只评估一次。
因此,如果answer
等于0
,则responses[answer]
等于1
,因此我们将1
添加到frequency[1]
。
编辑
下表显示了循环中frequency
的变化(旧值 => 新值):
answer response[answer] frequency[response[answer]]
------ ---------------- ---------------------------
0 1 frequency[1]: 0 => 1
1 2 frequency[2]: 0 => 1
2 6 frequency[6]: 0 => 1
3 4 frequency[4]: 0 => 1
... ... ...
10 1 frequency[1]: 1 => 2
等等。
声明:本站的技术帖子网页,遵循CC BY-SA 4.0协议,如果您需要转载,请注明本站网址或者原文地址。任何问题请咨询:yoyou2525@163.com.