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Need help with loop

hympert (4)
Hi everyone, I'm an absolute beginner here and I'm trying to learn C++ by myself through videos on youtube and other online resources. Here's a small program I practice using loop but somehow it doesn't work out as expected.

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  #include <iostream>

using namespace std;

int main()
{

    cout << "What is today's day?" << endl;
    cout << " m for Monday \n t for Tuesday \n w for Wednesday \n T for Thursday \n f for Friday \n s for Saturday \n S for Sunday." << endl;





    for(char input ; !(input == 'e') ; cin >> input){

            switch(input){

                case 'm':
                    cout << "It's Monday!" << endl;
                    break;

                case 't':
                    cout << "It's Tuesday!" << endl;
                    break;

                case 'w':
                    cout << "It's Wednesday!" << endl;
                    break;

                case 'T':
                    cout << "It's Thursday!" << endl;
                    break;

                case 'f':
                    cout << "It's Friday!" << endl;
                    break;

                case 's':
                    cout << "It's Saturday!" << endl;
                    break;

                case 'S':
                    cout << "It's Sunday!" << endl;
                    break;

                //Everything else except for 'e' and 7 cases above
                default:
                    cout << "Your input is not valid" << endl;
                   
            }

        }
        
        //If enter 'e' program will end by displaying this message.
 
        cout << "Have a nice day!";
    }

What I'm trying to do is to ask a user to input a character represent the day of the week. Everything works just fine. The problem is that when I build and run the program, it automatically displays "It's Tuesday!" before I enter any character. I also try with 'if' and 'while', but 'for' is a better suit. I've been revising my code many times but still couldn't figure out why. Any help will be appreciated. Thanks in advance.
Chriscpp (368)
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#include <iostream>

using namespace std;

int main()
{

    cout << "What is today's day?" << endl;
    cout << " m for Monday \n t for Tuesday \n w for Wednesday \n T for Thursday \n f for Friday \n s for Saturday \n S for Sunday." << endl;





    for(char input ; cin >> input,!(input == 'e') ; ){//<<<<<<<<<<<

            switch(input){

                case 'm':
                    cout << "It's Monday!" << endl;
                    break;

                case 't':
                    cout << "It's Tuesday!" << endl;
                    break;

                case 'w':
                    cout << "It's Wednesday!" << endl;
                    break;

                case 'T':
                    cout << "It's Thursday!" << endl;
                    break;

                case 'f':
                    cout << "It's Friday!" << endl;
                    break;

                case 's':
                    cout << "It's Saturday!" << endl;
                    break;

                case 'S':
                    cout << "It's Sunday!" << endl;
                    break;

                //Everything else except for 'e' and 7 cases above
                default:
                    cout << "Your input is not valid" << endl;

            }

        }

        //If enter 'e' program will end by displaying this message.

        cout << "Have a nice day!";
    }
hympert (4)
Thank you, it works!!!! Can you explain why my code doesn't work but your code works ?
Chriscpp (368)
your code
for(char input ; !(input == 'e') ; cin >> input)
your input is tying to do something without knowing what the input is, therefor input something before you do something with it so
for(char input ; cin >> input,!(input == 'e') ; )
hympert (4)
So if I don't set variable equal to something, then it will automatically get a random value? I thought that the middle section of the for loop is for condition, does that mean that cin >> input is a condition? Thank you.
closed account (EwCjE3v7)
So if I don't set variable equal to something, then it will automatically get a random value? I thought that the middle section of the for loop is for condition, does that mean that cin >> input is a condition? Thank you.


Yes std::cin >> can be used for a condition such as 
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int i = 0
// Make sure we get input
if (std::cin >> i) {
.....
}

// Keep getting input into i
while (std::cin >> I) {}

// declare i2 and initialise it to 0, get input into it and add one to it
for (int i2 = 0; std::cin >> i2; ++i2) {...}
Last edited on
hympert (4)
Thank you so much for your clear illustration CaptainBlastXD and Chriscpp for correcting my code.
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