I wanted to see how I could enhance the efficiency of this program, in terms of conciseness and security.

1. How can I ensure that the user will not break the program by typing a character or a special symbol when I have asked for a number?

2. Are there any functions in C that can recognize if the data that the user has input is a digit or a character?

I am new to programming. Any help would be appreciated. Thank You!

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

int main()
{
    //Declaring Variables
    float num1, num2;
    int op;
    char ans;

    //Getting the user to choose an option
Again:
    printf("\n\t\tMENU FOR OPERATIONS:\n ");
    printf("\t\t____________________\n\n");

    printf("1. Addition\n");
    printf("2. Subtraction\n");
    printf("3. Multiplication\n");
    printf("4. Division\n");
    printf("5. Modulus\n");
    printf("6. Power Function\n\n");
    printf("Enter the MENU option: ");
    scanf("%d", &op);

    while ( op != 1 && op != 2 && op != 3 && op != 4 && op != 5 && op != 6)
    {
        printf("\nYou entered an invalid MENU option!\n");
        printf("Kindly try again.\n\n");
        printf("Enter the MENU option: ");
        scanf("%d", &op);
    }


    //Getting the numbers from user
    printf("Enter the first number: ");
    scanf("%f", &num1);
    printf("Enter the second number: ");
    scanf("%f", &num2);

    //Implementing a switch statement for processing the input
    switch(op)
    {
    //Case for Addition function
    case 1:
        printf("Result = %.1f\n",  num1   num2 );
        break;

    //Case for Subtraction function
    case 2:
        printf("Result = %.1f\n", num1 - num2);
        break;

    //Case for Multiplication function
    case 3:
        printf("Result = %.1f\n", num1 * num2);
        break;

    //Case for Division function
    case 4:
        printf("Result = %.1f\n", num1 / num2 );
        break;

    //Case for Modulus function
    case 5:
        printf("Result: %d\n",(int)num1 % (int)num2);
        break;

    //Case for Power Function
    case 6:
        printf("Result: %.1f\n", pow(num1, num2));
        break;

    default:
        printf("You entered an invalid operator!\n\n");
        break;

    }
    //Asking the user if he wants to run the program again
    printf("\nDo you want to continue (Y/N)? ");
    ans = getche();
    ans = toupper(ans);

    //Implementing a while loop to get the user to enter a valid character
    while((ans != 'Y' ) && (ans != 'N'))
    {
        printf("\n\nYou must type a Y or an N!\n");
        printf("Do you want to continue (Y/N)? ");
        ans = getche();
        ans = toupper(ans);
    }

    //Implementing an if statement to ascertain whether the user wants to continue or quit
    if( ans == 'Y')
    {
        system("cls");
        goto Again;      //links the program to the start in case of a YES
    }
    else
    {
        exit(1);              //Successfully exits the program in case of a NO
    }
}

CodePudding user response：

1. Stop using scanf() as a user interface function. It is not designed to be used as such, and you can easily found plenty of reasons why. I personally like this. Use combination of fgets() and sscanf, if necessary.

2. Yes, in the ctypes.h, there are functions like isalpha and isdigit etc.

Additionally, do not use goto as a flow control element, ever, as it leads to hard to debug, hard to read, hard to follow through spaghetti code. If your program logic is implemented by goto, that almost always means you didn't think enough on it.

As a side note, by convention most C functions return 0 in case of success, and a non-zero value indicating some sort of error. Here, i,t is not much of a problem, but if you find yourself writing a library or such, you will annoy your users.