当用户输入无效数字时，如何给出打印语句错误'；s或字母C

我有一个while循环菜单系统，可以收集用户的输入。但是，可以选择的选项数量显然有限（在本例中为4和6）

菜单一：

我的第一个菜单使用用户输入的字母来选择动作。我想让用户得到一个printf语句，如果他们使用了菜单上未使用的任何字母，则说明他们输入了无效的字母。代码如下：

printf("\n\nOption | Action\n");
    printf("     Q | Quit\n");
    printf("     T | Loan Table\n");
    printf("     C | Calculate Loan\n");
    printf("     E | Explanation\n");
    printf("Select Option: ");
    fseek(stdin, 0, SEEK_END);
    scanf("%c", &menuChoice);
    menuChoice = toupper(menuChoice);

我目前使用的错误句柄是：

if(menuChoice != 'Q' || menuChoice != 'T' || menuChoice != 'C'  || menuChoice != 'E') 
    { 
    printf("Error! Choose a valid menu option.");        
    }

这显然不起作用，因为如果它不是E，例如，但仍然是C，它仍然会调出错误消息。我已经删除了这个

我的while循环目前使用它，但是它没有做任何事情，而且我对while循环在C中的工作方式仍然非常熟悉

我对此菜单的问题是，如何为此菜单调出打印语句错误

菜单二：

我的另一个菜单有点复杂，因为它使用数字系统。它基本上与上面的菜单相似，只是有数字。然而，还有更多的条件。菜单代码为：

printf("\nYou selected option C.\n");
        printf("\nLoan Calculator\n");
        printf("Option | Plan\n");
        printf("     1 | LF1\n");
        printf("     2 | LF2\n");
        printf("     3 | BBPL\n");
        printf("     4 | ILZERO\n");
        printf("     5 | ILFIVE\n");
        printf("     6 | LS5\n");
        printf("Select Plan: ");
        fseek(stdin, 0, SEEK_END);
        scanf("%d", &planCode);
        //CHECK IF IT IS A NUMBER BETWEEN 1 AND 6
        printf("Cost of car: ");
        fseek(stdin, 0, SEEK_END);
        scanf("%d", &carCost);
        //CHECK IF IT IS A NUMBER
        printf("Deposit: ");
        fseek(stdin, 0, SEEK_END);
        scanf("%d", &deposit);
        //CHECK IF IT IS A NUMBER
        printf("Length of Loan (years): ");
        fseek(stdin, 0, SEEK_END);
        scanf("%d", &loanLength);
        //CHECK IF IT IS A NUMBER AND IS BETWEEN 1 AND 10

如图所示，有相当多的条件。我尝试了很多方法来捕捉错误，但是程序总是会崩溃，或者即使不满足条件也会显示print语句

我试过

！isdigit（）

但是，即使是数字，它仍会播放该语句

如何捕捉这些错误

我是C语言的新手，他们对C语言的在线资源是有限的，希望你能提供帮助。提前谢谢

以下是我编写的全部代码，如果这还不够信息：

包括：

#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>

主要内容：

intmain（）
{
char menuChoice；
整数规划码；
成本、存款、贷款长度；
双重贷款初始；
双重贷款支付；
双铝酸盐；
双倍收费；
做
{
printf（“\n\n选项|操作\n”）；
printf（“Q|Quit\n”）；
printf（“贷款表”）；
printf（“C|Calculate Loan\n”）；
printf（“解释”）；
printf（“选择选项：”）；
fseek（stdin，0，SEEK_END）；
scanf（“%c”和menuChoice）；
menuChoice=toupper（menuChoice）；
如果（menuChoice=='T'）
{
printf（“\n您选择了选项T”。\n”）；
printf（“\nEndor Loan Details List\n”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“贷款供应商|贷款产品代码|初始费用|月费|利率%|最高贷款金额|最低贷款金额|\n”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“| 1 |叶友| LF1 | 150美元| 0美元| 6.14%| 70000美元| 5000美元|\n”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“| 2 |叶友| LF2 |$155 |$0 | 6.24%|$70000 |$1000 |\n”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“3家大银行150美元0美元6.30%| 80000美元| 5000美元”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“4 | ITSALOAN | ILZERO | 149美元| 0美元| 7.10%*| 50000美元| 1000美元|\n”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“| 5 | ITSALOAN | ILFIVE | 140美元| 5美元| 7.10%*| 50000美元| 1000美元|\n”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“6只贷款绵羊5只| 349美元| 0只| 5.91%| 50000美元| 500美元|\n”）；
printf（“+-----------------------------------------------------------------------------------------------------------------------------------+\n”）；
printf（“注*：对于任何超过20000美元的贷款，ITSALOAN目前有一项特别促销活动，利率降至6.1%”；
}
如果（menuChoice=='C'）
{
printf（“\n您选择了选项C”。\n”）；
printf（“\n计算器\n”）；
printf（“选项|计划”）；
printf（“1 | LF1\n”）；
printf（“2 | LF2\n”）；
printf（“3 | BBPL\n”）；
printf（“4 | ILZERO\n”）；
printf（“5 | ILFIVE\n”）；
printf（“6 | LS5\n”）；
printf（“选择计划：”）；
fseek（stdin，0，SEEK_END）；
scanf（“%d”和平面代码）；
//检查它是否是介于1和6之间的数字
printf（“汽车成本：”）；
fseek（stdin，0，SEEK_END）；
scanf（“%d”、&carCost）；
//检查它是否是一个数字
printf（“存款：”）；
fseek（stdin，0，SEEK_END）；
scanf（“%d”和存款）；
//检查它是否是一个数字
printf（“贷款期限（年）：”；
fseek（stdin，0，SEEK_END）；
scanf（“%d”和贷款长度）；
//检查它是否是一个数字，并且介于1和10之间
如果（平面代码==1）
{
贷款初始=成本-存款；
如果
double calcPayment(double loanAnnualRate, double loan, int length)
{
    double retv;
    int payments;
    double mul;
    double rate;
    rate = loanAnnualRate / 12;
    payments = length * 12;
    mul = pow(1 + rate, payments);
    retv = (loan * mul * rate) / (mul - 1);
    return retv;
}

int main()
{
    char menuChoice;
    int planCode;
    int carCost, deposit, loanLength;
    double loanInitial;
    double loanPayments;
    double IALSpecialRate;
    double fee;
    do
    {
        printf("\n\nOption | Action\n");
        printf("     Q | Quit\n");
        printf("     T | Loan Table\n");
        printf("     C | Calculate Loan\n");
        printf("     E | Explanation\n");
        printf("Select Option: ");
        fseek(stdin, 0, SEEK_END);
        scanf("%c", &menuChoice);
        menuChoice = toupper(menuChoice);

        if (menuChoice == 'T')
        {
            printf("\nYou selected option T.\n");
            printf("\nVendor Loan Details List\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("|   | Loan Vendor | Loan Product Code | Initial Fee | Monthly Fee | Interest Rate % | Max. Loan Amount | Min. Loan Amount |\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("| 1 | Leaf-Friend | LF1               | $150        | $0          | 6.14%%         | $70,000          | $5,000           |\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("| 2 | Leaf-Friend | LF2               | $155        | $0          | 6.24%%         | $70,000          | $1,000           |\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("| 3 | Big Bank    | BBPL              | $150        | $0          | 6.30%%         | $80,000          | $5,000           |\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("| 4 | ITSALOAN    | ILZERO            | $149        | $0          | 7.10%%*        | $50,000          | $1,000           |\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("| 5 | ITSALOAN    | ILFIVE            | $140        | $5          | 7.10%%*        | $50,000          | $1,000           |\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("| 6 | Loan Sheep  | LS5               | $349        | $0          | 5.91%%         | $50,000          | $500             |\n");
            printf("+-----------------------------------------------------------------------------------------------------------------------+\n");
            printf("NOTE*: ITSALOAN has a special promotion on at the moment for any loan above $20000 the interest rate drops to 6.1%");
        }
        if (menuChoice == 'C')
        {
            printf("\nYou selected option C.\n");
            printf("\nLoan Calculator\n");
            printf("Option | Plan\n");
            printf("     1 | LF1\n");
            printf("     2 | LF2\n");
            printf("     3 | BBPL\n");
            printf("     4 | ILZERO\n");
            printf("     5 | ILFIVE\n");
            printf("     6 | LS5\n");
            printf("Select Plan: ");
            fseek(stdin, 0, SEEK_END);
            scanf("%d", &planCode);
            //CHECK IF IT IS A NUMBER BETWEEN 1 AND 6
            printf("Cost of car: ");
            fseek(stdin, 0, SEEK_END);
            scanf("%d", &carCost);
            //CHECK IF IT IS A NUMBER
            printf("Deposit: ");
            fseek(stdin, 0, SEEK_END);
            scanf("%d", &deposit);
            //CHECK IF IT IS A NUMBER
            printf("Length of Loan (years): ");
            fseek(stdin, 0, SEEK_END);
            scanf("%d", &loanLength);
        //CHECK IF IT IS A NUMBER AND IS BETWEEN 1 AND 10
        if (planCode == 1)
        {
            loanInitial = carCost - deposit;

            if (loanInitial < 5000.00)
            {
                printf("\nSorry! Your loan is too low to be used with LF1.\nTry either LF2, ILZERO or ILFIVE.\n");
            }
            if (loanInitial > 70000.00)
            {
                printf("\nSorry! Youe loan is too high to be used with LF1.\nTry BBPL.\n");
            }
            if (loanInitial >= 5000.00 && loanInitial <= 70000.00)
            {
                loanPayments = calcPayment(0.0614, loanInitial, loanLength);
                fee = 150;

                printf("Loan Size                    : $ %8.2lf", loanInitial);
                printf("\nTotal Repayment              : $ %8.2lf", loanPayments * 12 * loanLength + fee);
                printf("\nMonthly Repayments           : $ %8.2lf", loanPayments);
                printf("\nAnnual Repayment(s)          : $ %8.2lf", loanPayments * 12);
                printf("\nTotal Repayment Without Fees : $ %8.2lf", loanPayments * 12 * loanLength);
                printf("\nTotal Fees                   : $ %8.2lf", fee);
                printf("\nActual Loan Cost             : $ %8.2lf", loanPayments * 12 * loanLength + fee - loanInitial);
            }
        }
        if (planCode == 2)
        {
            loanInitial = carCost - deposit;

            if (loanInitial < 5000.00)
            {
                printf("\nSorry! Your loan is too low to be used with LF2.\nTry LS5\n");
            }
            if (loanInitial > 70000.00)
            {
                printf("\nSorry! Youe loan is too high to be used with LF2.\nTry BBPL.\n");
            }
            if (loanInitial >= 1000.00 && loanInitial <= 70000.00)
            {
                loanPayments = calcPayment(0.0624, loanInitial, loanLength);
                fee = 155;

                printf("Loan Size                     : $ %8.2lf", loanInitial);
                printf("\nTotal Repayment               : $ %8.2lf", loanPayments * 12 * loanLength + fee);
                printf("\nMonthly Repayments            : $ %8.2lf", loanPayments);
                printf("\nAnnual Repayment(s)           : $ %8.2lf", loanPayments * 12);
                printf("\nTotal Repayment Without Fees  : $ %8.2lf", loanPayments * 12 * loanLength);
                printf("\nTotal Fees                    : $ %8.2lf", fee);
                printf("\nActual Loan Cost              : $ %8.2lf", loanPayments * 12 * loanLength + fee - loanInitial);
            }
        }
        if (planCode == 3)
        {
            loanInitial = carCost - deposit;

            if (loanInitial < 5000.00)
            {
                printf("\nSorry! Your loan is too low to be used with BBPL.\nTry either LF2, ILZERO or ILFIVE.\n");
            }
            if (loanInitial > 80000.00)
            {
                printf("\nSorry! Youe loan is too high to be used with BBPL.\nTry a cheaper car below $80,000.\n");
            }
            if (loanInitial >= 5000.00 && loanInitial <= 80000.00)
            {
                loanPayments = calcPayment(0.063, loanInitial, loanLength);
                fee = 150;

                printf("Loan Size                    : $ %8.2lf", loanInitial);
                printf("\nTotal Repayment              : $ %8.2lf", loanPayments * 12 * loanLength + fee);
                printf("\nMonthly Repayments           : $ %8.2lf", loanPayments);
                printf("\nAnnual Repayment(s)          : $ %8.2lf", loanPayments * 12);
                printf("\nTotal Repayment Without Fees : $ %8.2lf", loanPayments * 12 * loanLength);
                printf("\nTotal Fees                   : $ %8.2lf", fee);
                printf("\nActual Loan Cost             : $ %8.2lf", loanPayments * 12 * loanLength + fee - loanInitial);
            }
        }
        if (planCode == 4)
        {
            loanInitial = carCost - deposit;

            if (loanInitial < 1000.00)
            {
                printf("\nSorry! Your loan is too low to be used with ILFIVE.\nTry LS5.\n");
            }
            if (loanInitial > 50000.00)
            {
                printf("\nSorry! Youe loan is too high to be used with ILFIVE.\nTry either LF1, LF2, BBPL or LS5.\n");
            }
            if (loanInitial >= 1000.00 && loanInitial <= 50000.00)
            {
                if (loanInitial >= 20000) { IALSpecialRate = 0.061; }
                else IALSpecialRate = 0.071;
                loanPayments = calcPayment(IALSpecialRate, loanInitial, loanLength);
                fee = 149;

                printf("Loan Size                    : $ %8.2lf", loanInitial);
                printf("\nTotal Repayment              : $ %8.2lf", loanPayments * 12 * loanLength + fee);
                printf("\nMonthly Repayments           : $ %8.2lf", loanPayments);
                printf("\nAnnual Repayment(s)          : $ %8.2lf", loanPayments * 12);
                printf("\nTotal Repayment Without Fees : $ %8.2lf", loanPayments * 12 * loanLength);
                printf("\nTotal Fees                   : $ %8.2lf", fee);
                printf("\nActual Loan Cost             : $ %8.2lf", loanPayments * 12 * loanLength + fee - loanInitial);
            }
        }
        if (planCode == 5)
        {
            loanInitial = carCost - deposit;

            if (loanInitial < 1000.00)
            {
                printf("\nSorry! Your loan is too low to be used with ILFIVE.\nTry LS5.\n");
            }
            if (loanInitial > 50000.00)
            {
                printf("\nSorry! Youe loan is too high to be used with ILFIVE.\nTry either LF1, LF2, BBPL or LS5.\n");
            }
            if (loanInitial >= 1000.00 && loanInitial <= 50000.00)
            {

                if (loanInitial >= 20000) { IALSpecialRate = 0.061; }
                else IALSpecialRate = 0.071;

                loanPayments = calcPayment(IALSpecialRate, loanInitial, loanLength);
                loanPayments = calcPayment(0.071, loanInitial, loanLength);
                fee = 40;

                printf("Loan Size                    : $ %8.2lf", loanInitial);
                printf("\nTotal Repayment              : $ %8.2lf", loanPayments * 12 * loanLength + fee + (60 * loanLength));
                printf("\nMonthly Repayments           : $ %8.2lf", loanPayments + 5);
                printf("\nAnnual Repayment(s)          : $ %8.2lf", loanPayments * 12 + 60);
                printf("\nTotal Repayment Without Fees : $ %8.2lf", loanPayments * 12 * loanLength);
                printf("\nTotal Fees                   : $ %8.2lf", fee);
                printf("\nActual Loan Cost             : $ %8.2lf", loanPayments * 12 * loanLength + fee - loanInitial + (60 * loanLength));
            }
        }
        if (planCode == 6)
        {
            loanInitial = carCost - deposit;

            if (loanInitial < 500.00)
            {
                printf("\nSorry! Your loan is too low to be used with LS5.\n");
            }
            if (loanInitial > 55000.00)
            {
                printf("\nSorry! Youe loan is too high to be used with LS5.\nTry either LF1, Lf2 or BBPL.\n");
            }
            if (loanInitial >= 500.00 && loanInitial <= 55000.00)
            {
                loanPayments = calcPayment(0.0591, loanInitial, loanLength);
                fee = 349;

                printf("Loan Size                    : $ %8.2lf", loanInitial);
                printf("\nTotal Repayment              : $ %8.2lf", loanPayments * 12 * loanLength + fee);
                printf("\nMonthly Repayments           : $ %8.2lf", loanPayments);
                printf("\nAnnual Repayment(s)          : $ %8.2lf", loanPayments * 12);
                printf("\nTotal Repayment Without Fees : $ %8.2lf", loanPayments * 12 * loanLength);
                printf("\nTotal Fees                   : $ %8.2lf", fee);
                printf("\nActual Loan Cost             : $ %8.2lf", loanPayments * 12 * loanLength + fee - loanInitial);
            }
        }
    }
    if (menuChoice == 'E') { printf("\nYou selected option E.\n"); }
    if (menuChoice == 'Q')
    {
        printf("\nExiting Program...\n");
        exit(0);
    }
} while (menuChoice != 'Q' || menuChoice != 'T' || menuChoice != 'C' || menuChoice != 'E');
printf("\nPlease Choose a valid option.\n"); 

_getch;
return 0;

switch (menuChoice)
{ 
  case 'Q': 
    do_whatever_q_does();
    break; 
  case 'E': 
    do_whatever_e_does();
    break;
  (and so on)
  default :
    throw_error_message();
}

bool readAndValidateInput(int* input, int min, int max) {
fseek(stdin, 0, SEEK_END);
if (scanf(" %d", input) != 1) {
    fprintf(stderr, "Invalid input.\n");
    return false;
}

if (min == 0 && max == 0)
    return true;

if (*input < min || *input > max) {
    fprintf(stderr, "Input not in range.\n");
    return false;
}

return true; }

        do {
           printf("Select Plan: ");
           //CHECK IF IT IS A NUMBER BETWEEN 1 AND 6
        } while (!readAndValidateInput(&planCode, 1, 6))

        do {
            printf("Cost of car: ");
            // supply 0 for min and max to omit range validation
        } while(!readAndValidateInput(&carCost, 0, 0));