c - 我的代码中的功能不起作用

Question

我尝试运行该程序，但它运行不正确。问题出在函数上，但我不知 Prop 体在哪里。我首先声明了这些函数，然后尝试在 main 中调用它们。但是，我不确定情况是否如此。我认为问题出在函数定义上？但我不知道还能做什么。如果有人能看一下并向我指出，那就太好了。

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

float computeMonthlyPayment(float p, float YearRate, float YearTerm);
float computeMonthlyInterest(float p, float YearRate);
void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);
void printTable(float MonthlyPayment, float p, float YearRate,float YearTerm);

int main()
{

    float n, p, r, MonthlyPayment, YearRate, YearTerm;

    printf("Enter the loan amount: ");
    scanf("%f", &p);

    if (p <= 0.0)
        printf("\nERROR: Invalid rate; must be greater than 0\n");
        while (p <= 0.0)
        {
            printf("\nEnter the loan amount: ");
            scanf("%f", &p);
        }

    printf("\nEnter annual interest rate: ");
    scanf("%f", &YearRate);

    if (YearRate <= 0.0 || YearRate > 30.0)
        printf("\nERROR: Invalid rate; must be > 0.0 amd <= 30.0.\n");
        while (YearRate <= 0.0 || YearRate > 30.0)
        {
            printf("\nEnter annual interest rate: ");
            scanf("%f", &YearRate);
        }

    printf("\nEnter the term of the loan (in years): ");
    scanf("%f", &YearTerm);

    if (YearTerm <= 0.0)
        printf("\nERROR: Invalid rate; must be greater than 0\n");
        while (YearTerm <= 0.0)
        {
            printf("\nEnter the term of the loan (in years): ");
            scanf("%f", &YearTerm);
        }


    float computeMonthlyInterest(float p, float YearRate);
    float computeMonthlyPayment(float p, float YearRate, float YearTerm);
    void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);


    return 0;
}


float computeMonthlyPayment(float p, float YearRate, float YearTerm)
{
    float r = YearRate/12;
    float n = YearTerm*12;
    float MonthlyPayment = 0;

    MonthlyPayment = (r*p)/1-((1+r)/n);

    return MonthlyPayment;
}


float computeMonthlyInterest(float p, float YearRate)
{
    float r = 0;
    r = ((YearRate)/12)/12;

    return r;

}


void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n)
{

    printf("LOAN INFORMATION\n");
    printf("-----------------------\n");
    printf("Initial loan amount:  %.2f\n", p);
    printf("Annual interest rate:  %.3f\n", YearRate);
    printf("Monthly interest rate:  %.3f\n", r);
    printf("Term of loan (years):  %f\n", YearTerm);
    printf("Term of loan (months):  %f\n", n);
    printf("Monthly payment amount:  %.2f\n", MonthlyPayment);

}

Answer 1

看一下 main() 中的第 48..50 行。

int main()
{

    // ...

    float computeMonthlyInterest(float p, float YearRate);
    float computeMonthlyPayment(float p, float YearRate, float YearTerm);
    void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);

    // ...
}

这些是函数的原型(prototype)，而不是您实际调用它们的方式。您应该以与调用 printf() 或 scanf() 相同的方式调用它们，通过向它们传递适当的参数。就目前而言，您只是在 main() 中重新声明函数，而不是实际调用它们。尝试这样的事情:

int main()
{

    // ...

    r = computeMonthlyInterest(p, YearRate); // r should be labeled better.
    MonthlyPayment = computeMonthlyPayment(p, YearRate, YearTerm);
    printLoanInfo(p, MonthlyPayment, YearRate, r, YearTerm, n);

    // ...
}

但这仍然没有 100% 修复，因为 n 尚未初始化。虽然 printLoanInfo() 说明了它的用途(这也是我识别 r 的方式)，但您忘记在 main() 中设置它。所以..

int main()
{

    // ...

    r = computeMonthlyInterest(p, YearRate);
    n = YearTerm * 12; // You did this in computeMonthlyPayment(), but not here.
    MonthlyPayment = computeMonthlyPayment(p, YearRate, YearTerm);
    printLoanInfo(p, MonthlyPayment, YearRate, r, YearTerm, n);

    // ...
}

因此，考虑到这些更改，您的 main() 可能应如下所示:

int main()
{

    float n, p, r, MonthlyPayment, YearRate, YearTerm;

    printf("Enter the loan amount: ");
    scanf("%f", &p);

    if (p <= 0.0)
        printf("\nERROR: Invalid rate; must be greater than 0\n");
        while (p <= 0.0)
        {
            printf("\nEnter the loan amount: ");
            scanf("%f", &p);
        }

    printf("\nEnter annual interest rate: ");
    scanf("%f", &YearRate);

    if (YearRate <= 0.0 || YearRate > 30.0)
        printf("\nERROR: Invalid rate; must be > 0.0 amd <= 30.0.\n");
        while (YearRate <= 0.0 || YearRate > 30.0)
        {
            printf("\nEnter annual interest rate: ");
            scanf("%f", &YearRate);
        }

    printf("\nEnter the term of the loan (in years): ");
    scanf("%f", &YearTerm);

    if (YearTerm <= 0.0)
        printf("\nERROR: Invalid rate; must be greater than 0\n");
        while (YearTerm <= 0.0)
        {
            printf("\nEnter the term of the loan (in years): ");
            scanf("%f", &YearTerm);
        }


    // Remove these lines:
    // float computeMonthlyInterest(float p, float YearRate);
    // float computeMonthlyPayment(float p, float YearRate, float YearTerm);
    // void printLoanInfo(float p, float MonthlyPayment, float YearRate, float r, float YearTerm, float n);


    // Add these lines:
    r = computeMonthlyInterest(p, YearRate);
    n = YearTerm * 12;
    MonthlyPayment = computeMonthlyPayment(p, YearRate, YearTerm);
    printLoanInfo(p, MonthlyPayment, YearRate, r, YearTerm, n);


    return 0;
}