Question

Suppose that str1, str2, and str3 are string variables, and str1 \(=\) "English", str2 = "Computer Science", and str3 = "Programming". Evaluate the following expressions. a. \(\quad \operatorname{str} 1>=\operatorname{str} 2\) b. \(\quad\) str1 \(\quad !=\) "english" c. \(\operatorname{str} 3<\operatorname{str} 2\) d. \(\quad\) str \(2 \quad>=\) "Chemistry"

Short answer

a) true, b) true, c) false, d) true.

Step-by-step solution

Evaluate Expression a

Given str1 = "English" and str2 = "Computer Science", we compare if str1 is greater than or equal to str2. In string comparison, lexicographical order (dictionary order) is used. Since 'E' comes after 'C', "English" is greater than "Computer Science". Thus, the expression `str1 >= str2` evaluates to `true`.

Evaluate Expression b

Here, str1 is "English". We check if it is not equal to "english". String comparison is case-sensitive, so "English" is not equal to "english" (due to capitalization). Thus, the expression `str1 != "english"` evaluates to `true`.

Evaluate Expression c

Now we compare str3 = "Programming" with str2 = "Computer Science". Lexicographically, 'P' comes after 'C', so "Programming" is greater than "Computer Science". Therefore, the expression `str3 < str2` evaluates to `false`.

Evaluate Expression d

String comparison of `str2 >= "Chemistry"` means checking if "Computer Science" is greater than or equal to "Chemistry". Since 'C' (from "Computer Science") is equal to 'C' (from "Chemistry"), we look at the next letters. 'o' comes after 'h', so "Computer Science" is greater than "Chemistry". Therefore, `str2 >= "Chemistry"` evaluates to `true`.

Key concepts

Lexicographical Order

When you compare strings in C++, the comparison is based on lexicographical order. This is similar to dictionary order. For example, if you have two strings, "Apple" and "Banana", and you compare them, you would find that "Apple" comes before "Banana".
The comparison works by examining each character of the strings from left to right. The first character that is different in both strings determines which string is greater or smaller:

• If the character from the first string is earlier in the alphabet than the corresponding character from the second string, the first string is considered "less" than the other.
• Conversely, if it is later in the alphabet, then the first string is "greater".

In C++ code, you might use expressions like `(str1 >= str2)` to evaluate if one string is greater than or equal to another. This way of comparing is key when determining the order in expressions such as `str1 >= str2` from the exercise above.

Case Sensitivity in Strings

In C++, string comparisons are case-sensitive by default. This means that uppercase and lowercase characters are considered distinct and have different values. For instance, in the exercise, comparing "English" and "english" shows that they are not the same string.
This is because:

• The ASCII value of uppercase 'E' is different from the lowercase 'e'.
• Thus, when checking if `str1 != "english"`, the result is `true` because they differ in case.

It's essential to understand case sensitivity when working with strings, especially if your program involves user input. Sometimes, you may need to convert strings to the same case before comparison to avoid issues resulting from this case sensitivity, using functions like `tolower()` or `toupper()`.

Boolean Expressions in C++

Boolean expressions are critical in C++ programming, allowing decisions to be made based on conditions. They evaluate to either `true` or `false`. In the context of string comparisons, boolean expressions direct the flow by checking if a condition is met.
For example, using C++'s comparison operators, you can have expressions like:

• `(str1 >= str2)`, which checks if a string is greater than or equal to another.
• `(str1 != "english")`, which checks if two strings are not equal.
• `(str3 < str2)`, determining if one string is lexicographically less than another.
• `(str2 >= "Chemistry")`, which checks if a string comes after another string lexicographically or is the same.

These expressions are vital for controlling decision-making processes in your code, allowing specific actions based on whether these expressions evaluate to `true` or `false`.

Step-by-Step Problem Solving

Tackling problems step by step is a methodical approach to ensure you thoroughly understand and solve each part of a problem in coding. In our exercise, each expression was tackled systematically, demonstrating each step's reasoning.
Here's how you can approach it: 1. **Identify the Problem:** For each expression in the exercise, clearly determine what is being asked. 2. **Understand the Concepts:** Knowing lexicographical order and case sensitivity are crucial first steps. 3. **Break Down the Problem:** Handle each comparison individually and apply the relevant C++ concepts.

• For example, when comparing `(str1 >= str2)`, consider which is greater based on the order of characters.
• In `str1 != "english"`, focus on case sensitivity.
• In `(str3 < str2)`, decide if the order of characters makes one string smaller.
• Finally, in `str2 >= "Chemistry"`, consider both order and equality of strings.

Following a step-by-step approach ensures that no aspect of the problem is overlooked, making debugging easier and learning more efficient.