指针有三个功能

时间：2014-06-07 02:42:52

标签： c pointers

我是C的新手，正在尝试创建一个程序来查找银行帐户的复利。

我使用三个带指针的函数，一个用于获取数据，一个用于计算，另一个用于将数据打印到表中。我假设我对指针的混淆导致计算值在表中打印不正确。

目前我没有收到任何错误，但有关我的指针“默认为int”的一些警告。

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

//Function declarations
void GETDATA(double* StartAmnt, float* IntrRate, int* NumYears, int* StartYear);

void Mathemagic (double StartAmnt, float IntrRate, int NumYears, int StartYear,
                 float* IntrEarned, float* PercentGained,long double* FutureValue,
                 int* FutureYear);

void PRINTTABLE (double StartAmnt, float IntrRate, int NumYears, int StartYear,
                 float IntrEarned, float PercentGained,long double FutureValue,
                 int FutureYear);

int main(void)
{

    //Local Declarations
    double StartAmnt;
    float IntrRate;
    float IntrEarned;
    float PercentGained;
    long double FutureValue;

    int NumYears;
    int StartYear;
    int FutureYear;

    //Statements
    GETDATA (&StartAmnt, &IntrRate, &StartYear, &NumYears);

    Mathemagic (StartAmnt, IntrRate, StartYear, NumYears, &IntrEarned,
                &PercentGained, &FutureValue, &FutureYear);

    PRINTTABLE (StartAmnt, IntrRate, NumYears, StartYear, IntrEarned,
                PercentGained, FutureValue, FutureYear);


    return 0;
}//main

void GETDATA(double* StartAmnt, float* IntrRate, int* NumYears, int* StartYear)
{
    //Statements
    printf("COP 2220-51014 Project 2: Michael Walt\n\n");
    printf("Enter a Starting amount (dollars and cents): ");
    scanf("%lf", StartAmnt);
    printf("Enter an Interest rate (ex. 2.5 for 2.5%):   ");
    scanf("%f", IntrRate);
    printf("Enter the Number of years (integer number):  ");
    scanf("%d", NumYears);
    printf("Enter the Starting year (four digits):       ");
    scanf("%d", StartYear);
    return;
}//GETDATA


void Mathemagic (double StartAmnt, float IntrRate, int NumYears, int StartYear,
                 float* IntrEarned, float* PercentGained,long double* FutureValue,
                 int* FutureYear)
{
    //Statements

    *FutureValue = StartAmnt*pow((1+(IntrRate/100)),NumYears);

    *PercentGained =((*FutureValue - StartAmnt)/StartAmnt)*100;

    *IntrEarned = (*FutureValue-StartAmnt);

    *FutureYear = (StartYear+NumYears);

    return;
}//Mathemagic

PRINTTABLE(StartAmnt, IntrRate, NumYears, StartYear, IntrEarned,
           PercentGained, FutureValue, FutureYear)
{
    printf("\n+-----------------------------+--------------+\n");
    printf("| Description                 |  Input Data  |\n");
    printf("|-----------------------------+--------------|\n");
    printf("| Starting amount             | $  %.2f  |\n", StartAmnt);
    printf("| Interest rate               |        %f%% |\n", IntrRate);
    printf("| Number of Years             |        %d     |\n", NumYears);
    printf("| Starting year               |     %d     |\n", StartYear);
    printf("+-----------------------------+--------------+\n");
    printf("| Future value                |   Results    |\n");
    printf("|-----------------------------+--------------|\n");
    printf("| In %d the balance will be | $  %f  |\n", FutureYear, FutureValue);
    printf("| Interest earned             | $   %f  |\n", IntrEarned);
    printf("| Total percent gained        |       %f%% |\n", PercentGained);
    printf("+-----------------------------+--------------+\n");
    return;
}

2 个答案:

答案 0 :(得分：1)

您提供的参数顺序不正确，这是您的结果未正确计算的原因。您也没有在PRINTTABLE的函数定义中指定参数类型。它的工作现在正确。 

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

//Function declarations
void GETDATA(double* StartAmnt, float* IntrRate, int* NumYears, int* StartYear);

void Mathemagic (double StartAmnt, float IntrRate, int NumYears, int StartYear,
             float* IntrEarned, float* PercentGained,long double* FutureValue,
             int* FutureYear);

void PRINTTABLE (double StartAmnt, float IntrRate, int NumYears, int StartYear,
             float IntrEarned, float PercentGained,long double FutureValue,
             int FutureYear);

int main(void)
{

//Local Declarations
double StartAmnt;
float IntrRate;
float IntrEarned;
float PercentGained;
long double FutureValue;

int NumYears;
int StartYear;
int FutureYear;

//Statements
GETDATA (&StartAmnt, &IntrRate, &NumYears, &StartYear);

Mathemagic (StartAmnt, IntrRate, NumYears,  StartYear, &IntrEarned,
       &PercentGained, &FutureValue, &FutureYear);

PRINTTABLE (StartAmnt, IntrRate, NumYears, StartYear, IntrEarned,
        PercentGained, FutureValue, FutureYear);


return 0;
}//main

void GETDATA(double* StartAmnt, float* IntrRate, int* NumYears, int* StartYear)
{
//Statements
printf("COP 2220-51014 Project 2: Michael Walt\n\n");
printf("Enter a Starting amount (dollars and cents): ");
scanf_s("%lf", StartAmnt);
printf("Enter an Interest rate (ex. 2.5 for 2.5%):   ");
scanf_s("%f", IntrRate);
printf("Enter the Number of years (integer number):  ");
scanf_s("%d", NumYears);
printf("Enter the Starting year (four digits):       ");
scanf_s("%d", StartYear);
return;
}//GETDATA


void Mathemagic (double StartAmnt, float IntrRate, int NumYears, int StartYear,
             float* IntrEarned, float* PercentGained,long double* FutureValue,
             int* FutureYear)
{
//Statements

*FutureValue = StartAmnt*pow((1+(IntrRate/100)),NumYears);

*PercentGained =((*FutureValue - StartAmnt)/StartAmnt)*100;

*IntrEarned = (*FutureValue-StartAmnt);

*FutureYear = (StartYear+NumYears);

return;
}//Mathemagic

void PRINTTABLE(double StartAmnt, float IntrRate, int NumYears, int StartYear,
             float IntrEarned, float PercentGained,long double FutureValue,
             int FutureYear)
{
 printf("\n+-----------------------------+--------------+\n");
 printf("| Description                 |  Input Data  |\n");
 printf("|-----------------------------+--------------|\n");
 printf("| Starting amount             | $  %.2f  |\n", StartAmnt);
 printf("| Interest rate               |        %f%% |\n", IntrRate);
 printf("| Number of Years             |        %d     |\n", NumYears);
 printf("| Starting year               |     %d     |\n", StartYear);
 printf("+-----------------------------+--------------+\n");
 printf("| Future value                |   Results    |\n");
 printf("|-----------------------------+--------------|\n");
 printf("| In %d the balance will be | $  %f  |\n", FutureYear, FutureValue);
 printf("| Interest earned             | $   %f  |\n", IntrEarned);
 printf("| Total percent gained        |       %f%% |\n", PercentGained);
 printf("+-----------------------------+--------------+\n");
 return;
}

答案 1 :(得分：1)

主要问题是您的PRINTTABLE函数定义错误：

PRINTTABLE(StartAmnt, IntrRate, NumYears, StartYear, IntrEarned,
       PercentGained, FutureValue, FutureYear)

虽然它已被声明为

void PRINTTABLE (double StartAmnt, float IntrRate, int NumYears, int StartYear,
                 float IntrEarned, float PercentGained,long double FutureValue,
                 int FutureYear);

前

如果启用所有警告，您将看到此

*.c:76:1: warning: return type defaults to 'int' [-Wreturn-type]
 PRINTTABLE(StartAmnt, IntrRate, NumYears, StartYear, IntrEarned,
 ^
*.c:76:1: warning: conflicting types for 'PRINTTABLE' [enabled by default]
*.c:12:6: note: previous declaration of 'PRINTTABLE' was here
 void PRINTTABLE (double StartAmnt, float IntrRate, int NumYears, int StartYear,
      ^

因为您对PRINTTABLE有不同的声明和定义，并且编译器正在使用您的代码中出现的最后一个。在C99之前，没有声明类型，所有参数都默认为int类型，返回值也暗示为int，从而使冲突类型警告在上面。

因此，它会在错误的转换和格式中引起许多其他警告，如

*.c:82:5: warning: format '%f' expects argument of type 'double', but argument 2 has type 'int' [-Wformat=]
     printf("| Starting amount             | $  %.2f  |\n", StartAmnt);

那是因为没有类型，StartAmnt将是int并且你将它打印为double

另一个问题是第49行，你错过了百分号

printf("Enter an Interest rate (ex. 2.5 for 2.5%):   ");
                                               ↑

您也使用了错误的格式。 FutureValue类型为long double，但您要按%f打印它。它应该是%Lf。

printf("| In %d the balance will be | $  %f  |\n", FutureYear, FutureValue);

无论如何，如果您正在使用MSVC，那么double和long double是相同的，因为很久以前它已经放弃了对80位扩展精度类型的支持。我也不知道你为什么要使用混合浮点数，双倍和长双倍，它只是花费你时间来转换类型。在大多数应用中，长双倍是不必要的，因为它需要更多的空间，并且由于更高的精度和旧x87的使用而更慢。通常，double是推荐的类型。浮子最常用于存储，因为精度非常有限。

不要将ALL CAPS用于那样的函数或变量

相关问题
最新问题