CODEWITHSUNDEEP
cinputmenu
Moms
Moms

Reputation: 165

How to give a print statement error when the user inputs an invalid number's or letter in C

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;

}

Upvotes: 0

Views: 552

Answers (2)

Redouane
Redouane

Reputation: 430

If i were you i may validate scanf input for Menu Two using my little function below:

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; }

First parameter is pointer where input value will be stored, second and third parameter is range that the input will be check on. you can supply 0 to min and max if you want no range checking.

and you can use it with a sub do-while loop in your code this way:

        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 loops will run and prompt user for new input until it's a valid input, same way you can validate reset of inputs.

NOTE: Add #Include<stdbool> header in your file too.

You may also need to read about SCANF(...) and its return value meaning from this Link.

And you should consider Roux post to use switch statement for Menu One choices.

Upvotes: 2

user5726937
user5726937

Reputation:

Try swich statement, maybe? It lets you select actions for certain values of "menu choice", and an action for "all other values". Here's an example: 

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

Alternatively, if(menuChoice != 'Q' && menuChoice != 'T' && menuChoice != 'C' && menuChoice != 'E') should be "true" for anything except Q, T, C and E.

Upvotes: 1

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