CSC1110 - Conditionals and Loops

name: inverse
layout: true
class: taylor msoe
---
class: center, middle

.title[
  # Conditionals and Loops
]

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---
# Controlling Program Flow

* We may only want to perform one or more statements when a specific condition is met

--
* `if` statement in Java provides this functionality
``` Java
if ( /* CONDITIONAL */ ) {
    // One or more statements
}
```

--
``` Java
int number = in.nextInt()
if (number < 0) {
    System.out.println("You entered a negative number");
}
```

---
# `if` / `else`

* May wish to do different things depending on whether a condition is met

--
* `if` / `else` statement in Java provides this functionality
``` Java
if ( /* CONDITIONAL */ ) {
    // One or more statements (executed when condition met)
} else {
    // One or more statements (executed when condition not met)
```

---
# Nested `if`

* Can nest `if` statements inside `if` statements

--
``` Java
    int number = in.nextInt();
    if (number < 0) {
        System.out.println("You entered a negative number");
    } else {
        if (number > 0) {
            System.out.println("You entered a positive number");
        } else {
            System.out.println("You entered a number that is neither positive nor negative");
        }
    }
```

---
# `if` / `else if`

* We can simplify the syntax for the previous example as follows:

--
``` Java
    int number = in.nextInt();
    if (number < 0) {
        System.out.println("You entered a negative number");
    } else if (number > 0) {
        System.out.println("You entered a positive number");
    } else {
        System.out.println("You entered a number that is neither positive nor negative");
    }
```

---
# Boolean Operators

* More complicated boolean expressions can be constructed with these boolean operator:
  + `&&` — logical **AND**
  + `||` — logical **OR**
  + `!` — logical **NOT**

--
``` Java
boolean answer = true && true;  // true
answer = true && false;         // false
answer = true || false;         // true
answer = false || false;        // false
answer = true || false && true; // true
answer = true || false && true; // true
```

---
# Identifier Scope

* The **scope** of an identifier defines when it is available to be used

--
* An identifier is in scope from when it is declared until the closing brace `}` that matches the previous openning brace, `}`

--
``` Java
    public static void main(String[] args) {
        int i = 5;
        if (i < 10) {
            int j = i;
        }
    }
```

---
# While Loops

* A `while` loop is similar to an `if` statement
``` Java
    while ( /* CONDITIONAL */ ) {
        // One or more statements
    }
```

--
* It differs in that when the statement block is completed, the conditional is evaluated again
``` Java
    Scanner in = new Scanner(System.in);
    int sum = 0;
    while (in.hasNextInt()) {
        sum += in.nextInt();
    }
    System.out.println(sum);
```

---
# Do-While Loops

* A `do`-`while` loop checks the conditional after running the statement block
``` Java
    do {
        // One or more statements
    } while ( /* CONDITIONAL */ );
```

--
* Statement block always runs at least once
``` Java
    Scanner in = new Scanner(System.in);
    int evenCount = 0;
    int value;
    do {
        value = in.nextInt();
        if (value > 0 && value % 2 == 0) {
            evenCount += 1;
        }
    } while (value > 0);
    System.out.println("You entered " + evenCount + " even integers");
```

---
# For loops

* A `for` loop is useful when you want to repeat a know number of times
``` Java
    for ( /* INITIALIZATION */; /* CONDITIONAL */; /* UPDATE */ );
        // One or more statements
    }
```

--
* Example
``` Java
    String phrase = "This is our last loop type for today."
    int numSpaces = 0;
    for (int i = 0; i < phrase.length(); i++) {
        if (phrase.charAt(i) == ' ') {
            numSpaces++;
        }
    }
    System.out.println("Your phrase has " + numSpaces + " space in it");
```