C++ String manipulation - if stament

Question

I have the following code that works correctly. However after I add an else statement anything always evaluates to else

wgetstr(inputWin, ch); //get line and store in ch variable
        str = ch;          //make input from char* to string


        if(str=="m" || str=="M"){
            showFeedback("Data Memory Updated");
        }
        if(str=="p" || str=="P"){
            showFeedback("Program Memory Updated");
        }
        if(str=="g" || str=="G"){
            showFeedback("Accumulator, Program Counter, Zero Result Updated");
        }
        if(str=="e" || str=="E"){
            showFeedback("Editing Mode Enabled");
        }
        if(str=="c" || str=="C"){
            showFeedback("Program Copied Into Program Memory");
        }
        if(str=="r" || str=="R"){
            showFeedback("Executing Program");
        }
        if(str=="x" || str=="X"){
            showFeedback("Program Exited");
        }

All the previous evaluates correctly based on what the input is. ie If I enter "m" it calls the showeFeedback("Data Memory Updated") on so on, but if I add the following else statement, I always get "Invalid Command Entered" no matter what I enter.

else{
            showFeedback("Invalid Command Entered");
        }

Answer 1

All of those are separate if-statements. The else you added only goes with the last one. Change all but the first if to else if and it should work like you expect.

Answer 2

You need to use else if for everything except the first one.

So the simple change to your existing code:

        if(str=="m" || str=="M"){
            showFeedback("Data Memory Updated");
        }
        else if(str=="p" || str=="P"){
            showFeedback("Program Memory Updated");
        }
        else if(str=="g" || str=="G"){
            showFeedback("Accumulator, Program Counter, Zero Result Updated");
        }
        else if(str=="e" || str=="E"){
            showFeedback("Editing Mode Enabled");
        }
        else if(str=="c" || str=="C"){
            showFeedback("Program Copied Into Program Memory");
        }
        else if(str=="r" || str=="R"){
            showFeedback("Executing Program");
        }
        else if(str=="x" || str=="X"){
            showFeedback("Program Exited");
        }
        else
        {
            showFeedback("Invalid Command Entered");
        }

Answer 3

Another approach would be to use the switch statement that exists exactly for this kind of needs..

eg:

char str = ch[0];

switch (str)
{
    case 'm':
    case 'M': { showFeedback("Data Memory Updated"); break; }
    case 'p':
    case 'P': { showFeedback("Program Memory Updated"); break; }
    ....
    default: { showFeedback("Invalid Command Entered"); }
    /* default case is choosen if noone of the above is selected */
}

EDIT: just to explain your doubt in the comment, char str = ch[0] means take first character of the string and put it here .

if you want to check the complete string doing direct comparisons (with == or != ) is not adeguate: you should use strcmp(char* str1, char* str2) function that returns 0 if the two strings are equal.

Answer 4

Because when you add the else, its against the if(str=="x" || str=="X") line - so anything that is not an X will hit the else statement.

I think what you want are to convert all those ifs to "else if", except the first one of course.

Answer 5

需要注意的一件事，您可能希望使用toupper将字符串转换为大写，这样就不必将其与小写猜测进行“或”运算，这可能会使它更快一些。