Java (Find the future date with if else statements)

Question

I have a question that I can\'t figure it out , Thank you: Write a program that prompts the user to enter an integer for today\'s day of the week (Sunday is 0 ,Monday is 1 ,

Answer 1

As you need day-number to day-string twice, put it in a separate function. I want to show you a couple of possible approaches. Version 1, basic, simple and tidy:

// isolate the daynumber --> daystring in a function, that's tidier
String dayFor (int daynumber) {
    String dayAsString = "ERROR";  // the default return value
    switch(dayNumber) {
        case 0 :
            dayAsString = "Sunday";
            break;
        case 1 :
            dayAsString = "Monday";
            break;
        // and so on, until
        case 6 :
            dayAsString = "Saturday";
            break;
     }
     return dayAsString;
}

A much shorter version that uses an array instead of the switch statement:

String dayFor (int daynumber) {
    String dayStrings[] = new String[]{"Sunday","Monday", .... "Saturday"};
    // notice that daynumber's modulo is used here, to avoid index out of
    // bound errors caused by erroneous daynumbers:
    return dayStrings[daynumber % 7];
}

It might be tempting to try something along the lines of the following function where each case returns immediately, but having multiple return statements is discouraged. Just showing it here because it is technically possible, and you'll encounter it sometimes

String dayFor (int daynumber) {
    switch(dayNumber) {
        case 0 :
            return "Sunday";
        case 1 :
            return "Monday";

        // and so on, until

        case 6 :
            return "Saturday";
     }
     // normally not reached but you need it because the compiler will
     // complain otherwise anyways.
     return "ERROR";
}

After this rather long intro the main function becomes short and simple. After the input you just need:

// present day + elapsed modulo 7 = the future day
int future = (day + elapsed) % 7;
System.out.print("Today is " + dayFor(day) + " and the future day is " + dayFor(future) );

Don't forget to add code to check your inputs!