quizPrep.md

Week 2 Quiz Prep

Disclaimer: This document is meant to supplement other studying materials, not replace them

Concepts

• Arrays
• Loops
• Functions
• CS Voices
  
  

You can use a code playground on the CS 125 website to follow along and test the code! https://cs125.cs.illinois.edu/

Conceptual Overview

(These will be shorter from now on in the interesting of making more practice problems)

Arrays

• Arrays in Java are a way of ordering data, and they are indexed starting at 0
• The last element of the array is at the index of the array's length - 1, not the array's length
• Once the length of an array has been declared it cannot be changed
• There are two ways to declare an array in Java. These examples focus on int arrays

1. int[] myArray = new int[3]; //type[] arrayName = new type[length]; 
2. int[] myArray = {1,2,3}; //initialize and declare in one line 

• To access the values in the array you should use the [] operators
• Out of Bounds errors meaning you are accesing an invalid value!!! Ex:

int[] myArray = new int[7];
myArray[7] = 3;  //Error >:(

Loops

A couple types of loops we have learned in this cass:

int i = 0;
while (i < 7) {
  i++;
}

for (int i = 0; i < 7; i++) { //start, condition, update
  // i is only accesible in here
}

//enhanced for loop
// the variable in the enhanced for loop isn’t the index, it’s the value at that index in the array
int[] myArray = new int[7];
for (int i : myArray) {
  System.out.println(i);
}

Dont forget about:
break; - Stops executing a loop entirely
continue; - Skips to the next iteration

Functions

Allow us to use a piece of code over and over again

Function syntax:

returnType functionName (parameterType parameterName) {
	//return something if needed; 
}

Important: The code in the function is not executed until it is called

void myFunction() {
 System.out.println("isnt java cool");
}

The above code will do nothing unless you call it like below:

void myFunction() {
 System.out.println("isnt java cool");
}
myFunction();

Functions can also take in arguments:

void myFunction(int a) {
 System.out.println(a);
}

Functions can also return values. These are not the same as print statements When a return is executed we exit the function Ex:

int myFunction() {
 return 7;
 //everything below here will not be executed
}

Practice Problems

I will add solutions after the quiz prep session Monday.

1. Write a function that prints out all the values of an array that is passed in.

Spoiler!

	void printArray(int[] a) {
	  for (int i : a) {
           System.out.println(i);
 	  }
  
	}
	

2. Write a function that takes in two arrays, and then returns the array that has the largest sum

Spoiler!

	int[] returnLargestSum(int[] one, int[] two) {
  	  int sumOne = 0;
  	  int sumTwo = 0;
  
  	  for (int i : one) {
    		sumOne += i;
  	  }
  	  for (int i = 0; i < two.length; i++) {
    		sumTwo += two[i];
 	  }
  
  	  if (sumOne > sumTwo) {
    		return one;
  	  } else {
    	       return two;
  	  }
	}
	

3. Uh oh. It appears a football player is deflating the footballs again >:(. Write a function that accepts an array of football pressures. If a PSI in the array is below 12.5 return true, otherwise return false.

Spoiler!

	boolean bradyDetector(double[] one) {
 	  for (double i : one) {
    	    if (i < 12.5) {
     	      return true;
    	    }
  	  }
  
  	return false;
	}

	

4. Write a function that accepts an int array, index, and an int value. Then change the index to the value and return the new array.

Spoiler!

	int[] changeValue(int[] myArray, int index, int value) {
  	   myArray[index] = value;
  	   return myArray;
	}


	

5. Hard: Write a function that determines if the passed in array has repeated numbers. Brute Force is a completely acceptable solution.

Spoiler!

	boolean areThereRepeats(int[] passedIn) {
  	   for (int i = 0; i < passedIn.length; i++) {
    		for (int j = 0; j < passedIn.length; j++) {
      		  if (i != j) {
        
        	     if (passedIn[i] == passedIn[j]) {
                        return true;
       		     }
      		  }
    		}
  	     }
 	   return false;
	}