c - C 中的 pow(user_inputed_data, 2) 函数

Question

我正在使用 C 进行编码。我试图让 pow 函数来解决这个问题。使用基数作为用户输入的变量。该程序要求用户计算一个简单的打开 jar 头的面积和成本。这是代码:

//Pre-processor Directives
#include <stdio.h>
#include <math.h>
#define PI 3.14159

//Start of function
int main(void)
{
    //Declared variables
    float base_area, height_area, total_area_per_container;
    float radius, height, cost_per_container, total_cost, cost_per_sq_cm;
    int containers;

    //user input
    //radius input
    printf("Enter radius of base in cm: ");
    scanf("%f", &radius);
    //height input
    printf ("Enter height of container in cm: ");
    scanf("%f", &height);
    //material cost
    printf("Enter material cost per square cm: ");
    scanf(" $%f", &cost_per_sq_cm);
    //amount of containers
    printf("Enter the number of containers to be produced: ");
    scanf("%d", &containers);

    //calcualtions of each container
    base_area = PI * pow(radius,2);
    height_area = 2 * PI * radius * height;
    total_area_per_container = base_area + height_area;

    //calculation of the cost of the material
    cost_per_container = total_area_per_container * cost_per_sq_cm;
    total_cost = containers * cost_per_container;

    //Print results
    printf("Surface area of container: %.2f cm\n", total_area_per_container);
    printf("Cost per container: $%.2f\n", cost_per_container);
    printf("Total production costs: $%.2f\n", total_cost);

    //exit program
    return (0);
}

如果我取出每个容器的注释计算下的 pow(radius,2) 并放入“radius * radius”，一切都会正常，我只是想测试一下 pow 函数是如何工作的。我觉得我做错了什么。我还使用 NetBeans IDE 8.0.2 来编写代码。

更新1:使用我的教练拥有的gcc编译器。在他的计算机上编译我的代码给了我这个错误的响应:

第一部分是一堆行话，说我正在将代码复制到他的计算机上，接下来的内容如下 - 存储我的东西的目录已被删除

In function `main':
undefined reference to `pow'
collect2: error: ld returned 1 exit status
gmake[2]: *** [dist/Debug/GNU-Linux-x86/hw5] Error 1
gmake[2]: Leaving directory
gmake[1]: *** [.build-conf] Error 2
gmake[1]: Leaving directory
gmake: *** [.build-impl] Error 2

BUILD FAILED (exit value 2, total time: 2s)

Answer 1

编译失败，因为您没有链接到数学库。尝试通过以下方式编译:

gcc infile.c -lm

其次，您的代码中有一个错误。 The scanf() calls are failing due to not "consuming/gobbling-up" the trailing newline character. Don't use scanf(): use fgets() and the atoX() and sscanf() functions if you must do string parsing like this.我的 getBuf() 函数中的 strtok() 调用只是为了将来您将此示例用于其他类型的字符串解析时使用。 fgets() 函数不像 scanf() 那样使用共享流缓冲区。

我已经更新了您的代码 list ，并且能够使用您建议的两种功率计算方法获得相同的结果。

代码列表

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/*******************************************************************************
 * Pre-processor Directives
 ******************************************************************************/
#include <stdio.h>  // printf()
#include <stdlib.h> // atof() will compile but return zero if this is missing
#include <math.h>   // pow()
#include <stdbool.h>    // bool

#define PI      M_PI
#define BUF_LEN     (256)


/*******************************************************************************
 * Function prototypes
 ******************************************************************************/
bool getBuf(char* buf);


/*******************************************************************************
 * Function definitions
 ******************************************************************************/
int main(void)
{
    //Declared variables
    float base_area, height_area, total_area_per_container;
    float radius, height, cost_per_container, total_cost, cost_per_sq_cm;
    int containers;
    char buf[BUF_LEN] = { 0 };

    // User input
    //radius input
    printf("Enter radius of base in cm: ");
    if ( !getBuf(buf) ) { return (-1); }
    radius = atof(buf);

    //height input
    printf ("Enter height of container in cm: ");
    if ( !getBuf(buf) ) { return (-1); }
    height = atof(buf);

    //material cost
    printf("Enter material cost per square cm: ");
    if ( !getBuf(buf) ) { return (-1); }
    cost_per_sq_cm = atof(buf);

    //amount of containers
    printf("Enter the number of containers to be produced: ");
    if ( !getBuf(buf) ) { return (-1); }
    containers = atoi(buf);

    //calcualtions of each container
    base_area = PI * pow(radius, 2.0);
    //base_area = PI * radius * radius;
    height_area = 2 * PI * radius * height;
    total_area_per_container = base_area + height_area;

    //calculation of the cost of the material
    cost_per_container = total_area_per_container * cost_per_sq_cm;
    total_cost = containers * cost_per_container;

    //Print results
    printf("Surface area of container: %.2f cm\n", total_area_per_container);
    printf("Cost per container: $%.2f\n", cost_per_container);
    printf("Total production costs: $%.2f\n", total_cost);

    //exit program
    return (0);
}

bool getBuf(char* buf)
{
    if (!buf)
    {
        printf("Bad input.\n");
        return false;
    }
    fgets(buf, BUF_LEN, stdin); // Get a string of data
    strtok(buf, "\n");      // Clear out trailing newline
    return true;
}

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示例输出

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gcc test.c -lm && ./a.out 
Enter radius of base in cm: 1
Enter height of container in cm: 2
Enter material cost per square cm: 3
Enter the number of containers to be produced: 4
Surface area of container: 15.71 cm
Cost per container: $47.12
Total production costs: $188.50

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