I have a while loop menu system that gathers the users inputs. However there are obviously a limited number of options to choose from (in this instance 4 and 6).
Menu One:
The first menu I have uses letters that the user inputs to select the action. I want the user to get a printf statement saying that they have entered an invalid letter if they use any of the letters that aren't used on the menu. This is the code below:
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);
My current error handle I use at the moment is:
if(menuChoice != 'Q' || menuChoice != 'T' || menuChoice != 'C' || menuChoice != 'E')
{
printf("Error! Choose a valid menu option.");
}
This obviously doesn't work because if it isn't E for example but is still C it will still pull up the error message. I have since removed this.
My while loop uses this at the moment however it doesn't do anything and I am still very novice on how while loops work in C.
My question for this menu is how do I pull up a print statement error for this menu?
Menu Two:
The other menu I have is a bit more complicated as it uses a number system. It is basically like the menu above but rather just with numbers. However there are more conditions. The menu code is:
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
As shown there are a fair more conditions. I have tried many ways of trying to catch the error however the program would always crash or would show the print statement even if the condition isn't met.
I have tried !isdigit() however it would still play the statement even if it was a digit.
How do I catch these errors?
I am fairly new to C and their is limit sources on C online, hope you can help. Thanks in advance
Here is the whole code I have written if this isn't enough information:
Includes:
#include <stdio.h>
#include <conio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>
Calculations:
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;
}
Main:
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;
}
答案 0 :(得分：2)
如果我是你，我可以使用下面的小功能验证菜单二的scanf输入：
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; }
第一个参数是指针，其中存储输入值，第二个和第三个参数是输入将被检查的范围。 如果你不想检查范围，你可以提供0到min和max。
并且您可以通过这种方式在代码中使用sub-do-while循环：
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));
Do-While循环将运行并提示用户输入新输入，直到它成为有效输入， 同样，您可以验证输入的重置。
注意：在您的文件中添加＃Include＆lt; stdbool ＆gt; 标题。
您可能还需要阅读有关SCANF（...）及其返回值的含义Link。
你应该考虑使用Roux帖子来为Menu One选择使用switch语句。
答案 1 :(得分：1)
尝试swich声明，也许吧？它允许您为“菜单选项”的某些值选择操作，并为“所有其他值”选择操作。这是一个例子：
switch (menuChoice)
{
case 'Q':
do_whatever_q_does();
break;
case 'E':
do_whatever_e_does();
break;
(and so on)
default :
throw_error_message();
}
或者，除了Q，T，C和E之外，if(menuChoice != 'Q' && menuChoice != 'T' && menuChoice != 'C' && menuChoice != 'E')应为“true”。