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CONDITIONAL STATEMENTS

If Statements in C++

Lesson Read the full explanation

While writing code in any language, you will have to control the flow of your program - you will want to execute a certain piece of code if a condition is satisfied, and some different code in case it is not.

If statements are used to make these decisions in code. The keyword if tells C++ to execute the code in the curly braces under certain conditions, defined in the parentheses. These conditions are known as boolean conditions and they may only be true or false.

When the condition evaluates to true, the program executes the statement inside the curly braces. When the boolean condition evaluates to false, the statement inside the curly braces will not execute. But what will happen then?

Normally nothing would happen. But with an else statement, an alternate block of code can be executed.

if (test expression) {
    // run code if test expression is true
}
else {
    // run code if test expression is false
}

When writing if statements, we usually compare two values using one or more comparison operators:

Operator Name Examples
== Equal  x == 5,  x == y
!= Not equal  x != 3,  x != y
> Greater than  x > 5,  x > y
< Less than  x < 8,  x < y
>= Greater than or equal to  x >= 4,  x >= y
<= Less than or equal to  x <= 3,   x <= y

We can also combine multiple conditional statements with the help of logical operators:

Operator Name Description Examples
&& And Returns true if both statements are true x < 5 && x < 10
|| Or Returns true if one of the statements is true x < 5 || x < 10
! Not Reverses the result, returns false if the result is true !(x < 5 && x < 10)

Let's go through some examples together to better understand how if-else statements work:

# Declare 2 variables and initialize them
int a = 2;
int b = 3;

// Prints "a equals 2"
if(a == 2) {
  cout << "a equals 2" << endl;
}

// Prints nothing
if(b != 3) {
  cout << "b is not equal to 3" << endl;
}

// Prints "b equals 3"
if(a == 2 && b - a == 1) {
  cout << "b is equal to 3" << endl;
}

// Prints "a = 2, b = 3"
if(a != 2 || b != 3) {
  cout << "Inside if" << endl;
}
else {
  cout << "a = 2, b = 3" << endl;
}

// Prints "a + b equals 5"
if(!(a + b == 5)) {
  cout << "a + b is not equal to 5" << endl;
}
else {
  cout << "a + b equals 5" << endl;
}

// Prints "a is even, b is odd"
if(a % 2 == 0) {
  if(b % 2 == 0) {
    cout << "Both a and b are even" << endl;
  }
  else {
    cout << "a is even, b is odd" << endl;
  }
}
else {
  if(b % 2 == 0) {
    cout << "a is odd, b is even" << endl;
  }
  else {
    cout << "Both a and b are odd" << endl;
  }
}

Assignment
Follow the Coding Tutorial and let's write some if-else statements.

Hint
Look at the examples above if you get stuck.

STEP 1 OF 6
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    C++ · CONDITIONAL STATEMENTS

    Nested Conditionals in C++, explained

    Introduction

    In this lesson, we will explore the concept of if statements in C++. These statements are fundamental in controlling the flow of a program based on certain conditions. Understanding how to use if statements effectively is crucial for making decisions in your code, which is a common requirement in many programming scenarios.

    Understanding the Basics

    The if statement allows you to execute a block of code only if a specified condition is true. If the condition is false, you can use an else statement to execute an alternative block of code. This is essential for making decisions in your programs.

    Here is a simple example:

    int x = 10;
if (x > 5) {
    // This block will execute because x is greater than 5
    cout << "x is greater than 5" << endl;
} else {
    // This block will not execute
    cout << "x is not greater than 5" << endl;
}

    Main Concepts

    Let's delve deeper into the key concepts and techniques involved in using if statements:

    • Comparison Operators: These operators are used to compare two values. Examples include == (equal), != (not equal), > (greater than), < (less than), >= (greater than or equal to), and <= (less than or equal to).
    • Logical Operators: These operators are used to combine multiple conditions. Examples include && (and), || (or), and ! (not).

    Here is an example that combines comparison and logical operators:

    int a = 3;
int b = 5;
if (a < b && b < 10) {
    cout << "Both conditions are true" << endl;
} else {
    cout << "At least one condition is false" << endl;
}

    Examples and Use Cases

    Let's look at some practical examples to understand how if statements can be used in various contexts:

    int age = 20;
if (age >= 18) {
    cout << "You are an adult." << endl;
} else {
    cout << "You are a minor." << endl;
}

int score = 85;
if (score >= 90) {
    cout << "Grade: A" << endl;
} else if (score >= 80) {
    cout << "Grade: B" << endl;
} else if (score >= 70) {
    cout << "Grade: C" << endl;
} else {
    cout << "Grade: F" << endl;
}

    Common Pitfalls and Best Practices

    When using if statements, it's important to avoid common mistakes and follow best practices:

    • Common Pitfalls:
      • Forgetting to use curly braces for multi-line blocks.
      • Using assignment operator = instead of comparison operator ==.
    • Best Practices:
      • Always use curly braces to define the scope of the if and else blocks, even for single-line statements.
      • Keep your conditions simple and readable.

    Advanced Techniques

    Once you are comfortable with basic if statements, you can explore more advanced techniques such as nested if statements and the ternary operator:

    int num = 10;
if (num > 0) {
    if (num % 2 == 0) {
        cout << "Positive even number" << endl;
    } else {
        cout << "Positive odd number" << endl;
    }
} else {
    cout << "Non-positive number" << endl;
}

// Ternary operator
string result = (num > 0) ? "Positive" : "Non-positive";
cout << result << endl;

    Code Implementation

    Here is a well-commented code snippet demonstrating the correct use of if statements:

    #include <iostream>
using namespace std;

int main() {
    int a = 2;
    int b = 3;

    // Check if a equals 2
    if (a == 2) {
        cout << "a equals 2" << endl;
    }

    // Check if b is not equal to 3
    if (b != 3) {
        cout << "b is not equal to 3" << endl;
    }

    // Check if a equals 2 and b - a equals 1
    if (a == 2 && b - a == 1) {
        cout << "b is equal to 3" << endl;
    }

    // Check if a is not equal to 2 or b is not equal to 3
    if (a != 2 || b != 3) {
        cout << "Inside if" << endl;
    } else {
        cout << "a = 2, b = 3" << endl;
    }

    // Check if a + b is not equal to 5
    if (!(a + b == 5)) {
        cout << "a + b is not equal to 5" << endl;
    } else {
        cout << "a + b equals 5" << endl;
    }

    // Check if a is even and b is odd
    if (a % 2 == 0) {
        if (b % 2 == 0) {
            cout << "Both a and b are even" << endl;
        } else {
            cout << "a is even, b is odd" << endl;
        }
    } else {
        if (b % 2 == 0) {
            cout << "a is odd, b is even" << endl;
        } else {
            cout << "Both a and b are odd" << endl;
        }
    }

    return 0;
}

    Debugging and Testing

    Debugging and testing are crucial for ensuring your if statements work as expected:

    • Debugging Tips:
      • Use print statements to check the values of variables and the flow of execution.
      • Check the conditions carefully to ensure they are correct.
    • Testing Tips:
      • Write test cases for different scenarios, including edge cases.
      • Use a testing framework like Google Test for more comprehensive testing.

    Example of a simple test case:

    #include <iostream>
using namespace std;

void testIfStatements() {
    int a = 2;
    int b = 3;

    if (a == 2) {
        cout << "Test 1 Passed" << endl;
    } else {
        cout << "Test 1 Failed" << endl;
    }

    if (b != 3) {
        cout << "Test 2 Failed" << endl;
    } else {
        cout << "Test 2 Passed" << endl;
    }
}

int main() {
    testIfStatements();
    return 0;
}

    Thinking and Problem-Solving Tips

    Here are some strategies for approaching problems related to if statements:

    • Break down complex conditions into simpler sub-conditions.
    • Use flowcharts to visualize the decision-making process.
    • Practice writing if statements with different types of conditions.

    Conclusion

    In this lesson, we covered the basics of if statements in C++, including comparison and logical operators, common pitfalls, best practices, and advanced techniques. Mastering these concepts is essential for making decisions in your code and writing efficient, maintainable programs. Keep practicing and exploring further applications to solidify your understanding.

    Additional Resources

    For further reading and practice problems, check out the following resources:

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