Explain creating a pyramid in Java

Question

I am in a beginner java programming class and currently reviewing loops. If there is one thing I just do not understand, it\'s pyramids. I have researched the book exercis

Answer 1

Let's First understand For loop:

For Loop:

It is structured around a finite set of repetitions of code. So if you have a particular block of code that you want to have run over and over again a specific number of times the For Loop is helpful.

Syntax:

for(initilization; conditional expression; increment expression)
{
    //repetition code here
}

eg:

int x = 7;
for (int i = 1; i <= x; i++){
    // statements
}

In this "int i=1" is an initialization part, the loop will iterate till condition is true that is (I <=x) replace the value of I and x(1<=7).

After this statement inside the loop body will be executed and in the end "i++" that is the value of "I" will be incremented (I will become 2).

This process will repeat every time till the condition (I <= x) is true.

---

Now lets understand how pattern are form:

ROW (1) * --> COLUMN
|   (2) **
|   (3) ***
|   (4) *****
v   (5) *******

As we can see there are two things that need to be considered first the number of rows and second the number of columns:

We use two loops to construct such structures, first outer loop for number of rows and second inner loop for number of columns.

CODE LOGIC: First divide the pyramid into 3 triangle.

####$
###$$@
##$$$@@
#$$$$@@@
$$$$$@@@@

1> First triangle (White spaces represented by #)

####
###
##
#

2> Second triangle (represented by $)

$
$$ 
$$$
$$$$
$$$$$

3> Third triangle (represented by @)

#
@
@@
@@@
@@@@

Together it will make a pyramid structure

---

Lets begin :

Now lets breakdown our pattern problem:

######1
#####212
####32123
###4321234
##543212345
#65432123456
7654321234567

We will break this into 3 triangles and every triangle will have its own loop inside the main loop for the number of rows. As we can see a number of rows required for our pattern are 7 so we will make the first loop to repeat till 7 rows are achieved.

main loop (for rows):

int x = 7;
for (int i = 1; i <= x; i++) { // main loop for number of rows

    // other 3 loops will come insidethe mail loop

}   

First inner loop: As we have seen in pattern logic that the first triangle will consist of white spaces or blank.

                output eg: (representing white spaces with #)



                            ######          
                            #####   
                            ####    
                            ###
                            ##
                            #       


for (int j = 1; j <= x - i; j++)    // j represent a column number 
   System.out.print("   ");  
// This will create blank spaces till the condition is true.




**condition explained:** j <= x - i

Value of "i" is "1" as this is the first time the main loop is running and ever since the value of "i" has not changed.

 **replace values:** 

when j = 1 : 1 <= 7-1 (will print) ######

//first iteration of main loop and inner loop.

after this control will go to the next loop i.e second inner loop:

j = 2 : 2 <= 7-1 (will print) #####

// on second iteration of main loop and inner loop.

after this control will go to the next loop i.e second inner loop:

j = 3 : 3 <= 7-1 (will print) ####

// on third iteration of main loop and inner loop.

after this control will go to the next loop i.e second inner loop:

j = 4 : 4 <= 7-1 (will print) ###

//on fourth iteration of main loop and inner loop.

after this control will go to the next loop i.e second inner loop:

j = 5 : 5 <= 7-1 (will print) ##
// on fifth iteration of main loop and inner loop.

after this control will go to the next loop i.e second inner loop:

j = 6 : 6 <= 7-1 (will print) #

//on sixth iteration of main loop and inner loop.

after this control will go to the next loop i.e second inner loop:

j = 7 : 7 <= 7-1 //end of first inner loop as (7<=6 is not true)

---

Second inner loop :

for (int k = i; k >= 1; k--) //second triangle
                System.out.print((k >= 10) ?+ k : "  " + k);  // ternary operator is used to check the printing logic

NOTE:

ternary operator syntax: result = testCondition ? value1 : value2

// if testcondition is true then result will get value1 else value 2

***DIY: (Take a paper pen)***
    Implement for loop logic and replace variables with values: 

First iteration: K=i (we know i=1) so k=1; k>=1 (Replacing variables we get 1>=1 which is true); execute statements.

Statement: System.out.print((k >= 10) ?+ k : " " + k); or if(1>=10)? then print value of "k" (that is 1)

else print vlaue of "k" with some spaces ahead k (in order to make the pyramid look even spaced)

NOTE: if you are getting confused with ternary operator then don't use it, you can simply wirte.

System.out.print("  " + k); // will give same output

after this control will go to the next loop i.e third inner loop:

                *Second innerloop is used to print this portion:* 


                             1
                            21
                           321
                          4321
                         54321      
                        654321
                       7654321      

Third inner loop: This loop is used to print the third triangle.

                            2
                            23
                            234
                            2345
                            23456
                            234567



for (int k = 2; k <=i; k++) //  loop column  
                System.out.print((k >= 10) ?+ k : "  " + k); 
                            or
                System.out.print("  " + k)

---

lets see full code:

    int x = 7;   

    for (int i = 1; i <= x; i++) {              // loop row

        for (int j = 1; j <= x - i; j++)        // loop column (Triangle one)
            System.out.print("   ");

        for (int k = i; k >= 1; k--)            // loop column (Triangle two)
            System.out.print(  "  " + k);

        for (int k = 2; k <=i; k++)             // loop column (Triangle three)
            System.out.print( "  " + k);

        System.out.println();                   // used to go on new line (new row)
    }