我最近在大学开始学习C语言，我今天的任务是写一个程序来计算一组结构中产品的平均价格。我被告知我的代码应该被分成不同的函数。我如何将printf for循环和平均价格for循环放在一个单独的函数中，然后在main()中调用它?
感谢您的提前回复。
#define n 2
struct products{
char name[30];
char brand[30];
double price;
int quantity;
};
int main()
{
struct products products_arr[n];
int i;
float sum,avg;
for (i=0;i<n;i++)
{
printf("Enter product/s:nn");
printf("Enter product name: n");
scanf("%s",products_arr[i].name);
printf("Enter product brand: n");
scanf("%s",products_arr[i].brand);
printf("Enter product price: n");
scanf("%lf",&products_arr[i].price);
printf("Enter product quantity: n");
scanf("%d",&products_arr[i].quantity);
}
for (i=0;i<n;i++)
{
printf("n%s - %s - %.2lf - %d",products_arr[i].name,
products_arr[i].brand,
products_arr[i].price,
products_arr[i].quantity);
printf("n");
}
for (i = 0; i < n; i++)
{
sum += products_arr[i].price;
}
avg = sum / n;
printf("nAverage = %.2f", avg);
return 0;
}
如何使用avg函数
double avg(struct products * prod, int sz){
double sum = 0;
for(int i = 0 ; i < sz; i++){
sum += prod[i].price;
}
return sum / sz;
}
注意，你必须传递一个指向数组开头的指针，加上数组的大小
现在在main
中调用它double average = avg(products_arr, n);
如果函数体在main体之后，则需要在main
之前前向声明avgdouble avg(struct products * prod, int sz);
你可以使用它作为执行其他功能的模型
既然您正在学习C语言，那么对于您现有的代码有几个注意事项。你真正的问题似乎是"如何将我的代码划分为单独的函数"。
有两种基本方法，
- 学习时，通常更容易编写程序，调试并工作，然后将类似的功能分离为单独的函数，或者随着经验的增长
- 你了解你需要创建的功能，以及它将如何与你现有的代码接口，并简单地编写一个新的函数来满足你的需求。
在你的情况下，写你的程序，然后把它放在你面前，这样你就可以把输入，计算和输出功能分开，这会给你一个很好的路线图，你需要你的函数做什么。
在第一次编写程序时，您可能想要改进代码的注意事项(此处和以后)在下面的注释中列出:
#include <stdio.h>
#include <string.h>
#define N 2 /* define as many as you need - UPPERCASE */
#define MAXC 30
#define BUFSZ 1024
typedef struct products { /* add a typedef to make type use convenient */
char name[MAXC];
char brand[MAXC];
double price;
int quantity;
} products;
int main (void)
{
char buf[BUFSZ] = ""; /* read buffer */
int i = 0;
double sum = 0., avg = 0.;
products products_arr[N] = {0}; /* initialize arrays all zero */
puts ("Enter products"); /* heading before loop */
for (i = 0; i < N; i++)
{
fputs ("n Enter product name : ", stdout);
/* read user input with fgets() to consume entire line */
if (fgets (products_arr[i].name, MAXC, stdin) == NULL) {
puts ("(user canceled input)");
return 0;
}
/* trim trailing 'n' with strcspn()
* strcspn (string, "n") // returns no. of chars to "n"
* string[strcspn (string, "n")] = 0; // overwrites 'n' with 0
*/
products_arr[i].name[strcspn (products_arr[i].name, "n")] = 0;
fputs (" Enter product brand : ", stdout);
if (fgets (products_arr[i].brand, MAXC, stdin) == NULL) {
puts ("(user canceled input)");
return 0;
}
products_arr[i].brand[strcspn (products_arr[i].brand, "n")] = 0;
fputs (" Enter product price : ", stdout);
if (fgets (buf, MAXC, stdin) == NULL) { /* read all input with fgets */
puts ("(user canceled input)");
return 0;
}
/* parse needed information from read-buffer with sscanf() */
if (sscanf (buf, "%lf", &products_arr[i].price) != 1) {
fputs ("error: invalid double value.n", stderr);
return 1;
}
fputs (" Enter product quantity : ", stdout);
if (fgets (buf, MAXC, stdin) == NULL) { /* read all input with fgets */
puts ("(user canceled input)");
return 0;
}
if (sscanf (buf, "%d", &products_arr[i].quantity) != 1) {
fputs ("error: invalid integer value.n", stderr);
return 1;
}
}
for (i = 0; i < N; i++)
{ /* add 'n' to end of format string, don't call printf() twice */
printf ("n%s - %s - %.2lf - %dn", products_arr[i].name,
products_arr[i].brand,
products_arr[i].price,
products_arr[i].quantity);
sum += products_arr[i].price; /* don't waste loop, sum here */
}
avg = sum / N;
printf("nAverage = %.2fn", avg); /* always end final output with n */
}
将代码划分为函数
有了Input、computation和Output的路线图，您可以很容易地识别与输入相关的代码——以及它需要哪些变量。你有一个最大的数组大小为N，你将需要作为参数传递给你的输入函数是产品的数组。然后，输入函数可以返回读取的产品数量(可以小于N)。当出现错误时，您可以返回一个负值，或者简单地返回错误发生时成功读取的产品数量，从而保留此时收集的数据。
/** read up to a max of N products from stdin
* return number of elements read on success (can be less than N),
* otherwise returns -1 if user cancels input with manual EOF
*/
int read_products (products *products_arr)
{
char buf[BUFSZ] = ""; /* read buffer */
int i = 0;
puts ("Enter products"); /* heading before loop */
for (i = 0; i < N; i++)
{
fputs ("n Enter product name : ", stdout);
/* read user input with fgets() to consume entire line */
if (fgets (products_arr[i].name, MAXC, stdin) == NULL) {
puts ("(user canceled input)");
return 0;
}
/* trim trailing 'n' with strcspn() // How?
* strcspn (string, "n") // returns no. of chars to "n"
* string[strcspn (string, "n")] = 0; // overwrites 'n' with 0
*/
products_arr[i].name[strcspn (products_arr[i].name, "n")] = 0;
fputs (" Enter product brand : ", stdout);
if (fgets (products_arr[i].brand, MAXC, stdin) == NULL) {
puts ("(user canceled input)");
return -1;
}
products_arr[i].brand[strcspn (products_arr[i].brand, "n")] = 0;
fputs (" Enter product price : ", stdout);
if (fgets (buf, MAXC, stdin) == NULL) { /* read all input with fgets */
puts ("(user canceled input)");
return -1;
}
/* parse needed information from read-buffer with sscanf() */
if (sscanf (buf, "%lf", &products_arr[i].price) != 1) {
fputs ("error: invalid double value.n", stderr);
return i;
}
fputs (" Enter product quantity : ", stdout);
if (fgets (buf, MAXC, stdin) == NULL) { /* read all input with fgets */
puts ("(user canceled input)");
return i;
}
if (sscanf (buf, "%d", &products_arr[i].quantity) != 1) {
fputs ("error: invalid integer value.n", stderr);
return 1;
}
}
return i;
}
对于你的平均函数，除了产品的数组，你还需要传递数组中包含的产品的数量(因为它可以小于N)。您总是将函数的返回类型与返回值的类型相匹配。这里你可以这样做:
/** computes the average of nelem product price
* returns average
*/
double products_avg (products *products_arr, int nelem)
{
int i = 0; /* initialize variables */
double sum = 0;
for (; i < nelem; i++) /* loop nelem times */
{
sum += products_arr[i].price; /* sum price */
}
return sum / nelem; /* return average */
}
最后，您的输出函数可以只打印单个产品。同样，除了数组之外，还需要传递数组中产品的数量。由于输出函数不需要返回一个值，它可以是类型void，因为不需要指示成功/失败，并且您不依赖于返回的任何计算值，例如
/** prints individual product's name, brand, price & quantity */
void products_print (products *products_arr, int nelem)
{
int i = 0; /* initialize variables */
for (; i < nelem; i++) /* loop nelem times */
{ /* add 'n' to end of format string, don't call printf() twice */
printf ("n%s - %s - %.2lf - %dn", products_arr[i].name,
products_arr[i].brand,
products_arr[i].price,
products_arr[i].quantity);
}
}
把它们放在一起，你的程序可以拆分为函数:
#include <stdio.h>
#include <string.h>
#define N 2 /* define as many as you need - UPPERCASE */
#define MAXC 30
#define BUFSZ 1024
typedef struct products { /* add a typedef to make type use convenient */
char name[MAXC];
char brand[MAXC];
double price;
int quantity;
} products;
/* function prototypes (will go in header file later) */
int read_products (products *products_arr);
double products_avg (products *products_arr, int nelem);
void products_print (products *products_arr, int nelem);
int main (void)
{
int nelem = 0;
double avg = 0.;
products products_arr[N] = {0}; /* initialize arrays all zero */
nelem = read_products (products_arr); /* read products assign return */
if (nelem < 1) { /* validate read_products return */
return 1;
}
avg = products_avg (products_arr, nelem); /* compute average */
products_print (products_arr, nelem); /* output products */
printf("nAverage = %.2fn", avg); /* always end final output with n */
}
/** read up to a max of N products from stdin
* return number of elements read on success (can be less than N),
* otherwise returns -1 if user cancels input with manual EOF
*/
int read_products (products *products_arr)
{
char buf[BUFSZ] = ""; /* read buffer */
int i = 0;
puts ("Enter products"); /* heading before loop */
for (i = 0; i < N; i++)
{
fputs ("n Enter product name : ", stdout);
/* read user input with fgets() to consume entire line */
if (fgets (products_arr[i].name, MAXC, stdin) == NULL) {
puts ("(user canceled input)");
return 0;
}
/* trim trailing 'n' with strcspn() // How?
* strcspn (string, "n") // returns no. of chars to "n"
* string[strcspn (string, "n")] = 0; // overwrites 'n' with 0
*/
products_arr[i].name[strcspn (products_arr[i].name, "n")] = 0;
fputs (" Enter product brand : ", stdout);
if (fgets (products_arr[i].brand, MAXC, stdin) == NULL) {
puts ("(user canceled input)");
return -1;
}
products_arr[i].brand[strcspn (products_arr[i].brand, "n")] = 0;
fputs (" Enter product price : ", stdout);
if (fgets (buf, MAXC, stdin) == NULL) { /* read all input with fgets */
puts ("(user canceled input)");
return -1;
}
/* parse needed information from read-buffer with sscanf() */
if (sscanf (buf, "%lf", &products_arr[i].price) != 1) {
fputs ("error: invalid double value.n", stderr);
return i;
}
fputs (" Enter product quantity : ", stdout);
if (fgets (buf, MAXC, stdin) == NULL) { /* read all input with fgets */
puts ("(user canceled input)");
return i;
}
if (sscanf (buf, "%d", &products_arr[i].quantity) != 1) {
fputs ("error: invalid integer value.n", stderr);
return 1;
}
}
return i;
}
/** computes the average of nelem product price
* returns average
*/
double products_avg (products *products_arr, int nelem)
{
int i = 0; /* initialize variables */
double sum = 0;
for (; i < nelem; i++) /* loop nelem times */
{
sum += products_arr[i].price; /* sum price */
}
return sum / nelem; /* return average */
}
/** prints individual product's name, brand, price & quantity */
void products_print (products *products_arr, int nelem)
{
int i = 0; /* initialize variables */
for (; i < nelem; i++) /* loop nelem times */
{ /* add 'n' to end of format string, don't call printf() twice */
printf ("n%s - %s - %.2lf - %dn", products_arr[i].name,
products_arr[i].brand,
products_arr[i].price,
products_arr[i].quantity);
}
}
使用/输出示例
两个示例完全相同，并且会产生相同的输出，例如:
$ ./bin/structavg
Enter products
Enter product name : foo
Enter product brand : fink
Enter product price : 23.44
Enter product quantity : 10
Enter product name : bar
Enter product brand : blink
Enter product price : 26.66
Enter product quantity : 10
foo - fink - 23.44 - 10
bar - blink - 26.66 - 10
Average = 25.05
看一遍，有问题就告诉我。