3.1. Conditionals

Conditional statements in Python and C++ are very similar.

3.1.1. Simple if

In Python, we write a simple if statement in the following way:

if condition:
    statement1
    statement2
    ...

In C++ this same pattern is simply written as:

if (condition) {
    statement1
    statement2
    ...
}

Once again you can see that in C++ the curly braces define a block rather than indentation. In C++ the parenthesis around the condition are required because if is technically a function that evaluates to true or false.

3.1.2. if else

The if-else statement in Python looks like this:

if condition:
    statement1
    statement2
    ...
else:
    statement1
    statement2
    ...

In C++ this is written as:

if (condition) {
    statement1
    statement2
    ...
}
else {
    statement1
    statement2
    ...
}

3.1.3. elif

C++ does not have an elif pattern like Python. In C++ you can get the functionality of an elif statement by nesting if and else. Here is a simple example in both Python and C++.

# demonstrates if,elif, and else statements in python def main(): grade = 85 if (grade < 60): print('F') elif (grade < 70): print('D') elif grade < 80: print('C') elif grade < 90: print('B') else: print('A') main()

In C++ we have a couple of ways to write this

// Shows how to use conditional statements #include <iostream> using namespace std; int main() { int grade = 85; if (grade < 60) { cout<<'F'<< endl; } else { /* if, elif, and else statement can be used inside of themselves to allow for sub options */ if (grade < 70) { cout<<'D'<< endl; } else { if (grade < 80) { cout<<'C'<< endl; } else { if (grade < 90) { cout<<'B'<< endl; } else { cout<<'A'<< endl; } } } } return 0; }

We can get closer to the look of the elif statement in C++ by taking advantage of the C++ rule that a single statement does not need to be enclosed in curly braces. Since the if is the only statement used in each else we can get away with the following.

//Shows how to put conditional statements together, //specfically putting "else if" after an "if" statement. #include <iostream> using namespace std; int main() { int grade = 85; if (grade < 60) { cout<<'F'<<endl; } else if (grade < 70) { cout<<'D'<<endl; } else if (grade < 80) { cout<<'C'<<endl; } else if (grade < 90) { cout<<'B'<<endl; } else cout<<'A'<<endl; return 0; }

3.1.3.1. Check Yourself

Q-4: T/F: It is necessary to have an else statement after an if statement. (Hint: Test it out in the code above.)

• True
• Not quite, try modifying the code above to test it out.
• False
• Good job!

3.1.4. switch

C++ also supports a switch statement that acts something like the elif statement of Python under certain conditions because the statement takes cases and checks the validity of the case against the code. It uses cases instead of conditions and the case must be based on integers or a user-defined data type called an enumerated constant.

To write the grade program using a switch statement we would use the following:

// Shows how to use a Switch statement. #include <iostream> using namespace std; int main() { int grade = 85; int tempgrade = grade/10; switch(tempgrade) { /*switch cases allow for different options based on the value of temp grade similar to if statements*/ case 10: case 9: cout << "The grade is A" << endl; break; case 8: cout << "The grade is B" << endl; break; case 7: cout << "The grade is C" << endl; break; case 6: cout << "The grade is D" << endl; break; default: cout << "The grade is F" << endl; } return 0; }

Frankly, the switch statement is not used very often. It is not as powerful as the else if model because the switch variable can only be compared for equality with an integer or something called an enumerated constant. Second it is very easy to forget to put in the break statement. Note above how cases 10 and 9 are coded together. If the break statement is left out then then the next alternative will be automatically executed. For example if the grade was 95 and the break was omitted from the case 9: alternative then the program would print out both (A and B.) So, you might want to just avoid it and use if…

3.1.4.1. Check Yourself

Q-6: When indicating the condition for a C++ if statement, what symbols are used?

• { }
• No. Try again.
• [ ]
• No. Try again.
• ( )
• Right!
• Any set of matching braces may be used.
• No. Try again.
• none of the above
• One of the above is indeed correct.

Q-7: When using a switch, what prevents all the cases from passing as correct?

• Ending statements with ;
• No. This is always needed.
• Using a break statement
• Good job!
• Enclosing each cases with { }
• No. Try again.
• Setting a default case
• No. This is a good idea, but it will not help.

Q-8: What symbol is used to indicate the “and” in C++ such as in a compound condition?

• ||
• No, this means "or".
• and
• No, this is Python.
• !
• No, this means "not"
• &&
• Very good!

You have attempted of activities on this page