Nested For Loops and Random

24au ver.

Note: this is for the Autumn 2024 iteration of CSE 121. Looking for a different quarter? Please visit https://courses.cs.washington.edu/courses/cse121/.

Nested For Loops¶

(loops inside loops, can be used to produce complex text patterns)

Example

for (int i = 1; i <= 5; i++>) {
    for (int j = 1; j <= (5 - i); j++) {
        System.out.print(".");  // print dots
    }
    System.out.println(i);  // print line number
}

Output

....1
...2
..3
.4
5

Update Statements¶

(common update statements in for loops)

Statement	Description
`i++`	increment `i` by `1`; same as `i = i + 1`
`i += 1`	increment `i` by `1`; same as `i = i + 1`
`i--`	decrement `i` by `1`; same as `i = i - 1`
`i -= 1`	decrement `i` by `1`; same as `i = i - 1`

Random¶

(produce random numbers)

import java.util.*;  // We must include this in order to use Random!

// Create a Random object
Random rand = new Random();

// Generating values
int a = rand.nextInt(10); // generating an integer in the range of 0 to 9
int b = rand.nextInt(10) + 1; // generating an integer in the range of 1 to 10
int c = rand.nextInt(7) + 4; // generating an integer in the range of 4 to 10

Methods¶

Method	Description
`nextInt()`	random integer
`nextInt(max)`	random integer between `0` (inclusive) and `max` (exclusive)
`nextDouble()`	random double between `0.0` (inclusive) and `1.0` (exclusive)

Formula for Generating a Random Number between min - max (inclusive)¶

Steps	Example
1. What is the desired min?	4
2. What is the desired max?	10
3. Calculate the range = max - min + 1	10 - 4 + 1 = 7
4. Substitute into: `rand.nextInt(range) + min`	`rand.nextInt(7) + 4`

Fenceposting¶

(pulling one iteration out of the loop)

Example

System.out.print(1);               // one number to start with
for (int i = 2; i <= 5; i++) {
    System.out.print(", " + i);    // commas between numbers
}
System.out.println();              // end the line

Output

1, 2, 3, 4, 5