Loops

In java, loops are sections of code that repeat while a certain condition is true. There is a common structure to all types of loops, such as:

• the control variable, called the loop counter
• this control variable must be initialized, i.e. it must have an initial value
• The increment/decrement of the control variable, which is modified each time the loop occurs
• The loop condition that determines if the looping should continue or the program should break from it.

While loops

This is how a standard while loop looks:

(source: https://www.developer.com/java/data/using-different-types-of-java-loops-looping-in-java.html\

Here's an example of a while loop in practice:

int counter = 1;   // Control variable initialized

// Condition for loop continuation
while (counter <= 10) {
   System.out.println(counter);
   counter++;     // Increment the control variable
}

/*
   At the end of this loop, counter == 11, and the statements will have executed 10 times. 
*/

Exercises

// 1.

int a = 0;
int b = 0;
while (a <= 15) {
    b += 2;
    a++;
}

// what is the value of 'b': ___ ?




// 2.

int a = 10;
int b = 1;

while (a < 0) {
    b *= 2;
    a--;
}

// what is the value of 'b': ___ ?



// 3.

int a = 2;
int b = 3;
int c = 4;

while (a < 10 || b < 15) {
    c++;
    a++;
    b++;
}

// what is the value of 'a': ___ ?

For loops

For loops are very similar to while loops except they have different initialization techniques. This is how a standard for loop looks:

(source: https://www.developer.com/java/data/using-different-types-of-java-loops-looping-in-java.html\)

Here is an example of a for loop in practice:

// For(<initialization>;<condition>;<increment>
for(int counter = 1; counter <= 10; counter++){
   System.out.println(counter);
}

// There are variations as well

int counter;
for( counter = 1; counter <= 10; counter++){
   //... Statements
}

int counter = 1;
for(; counter <= 10; counter++){
   //... Statements
}

int counter = 1;
for(; counter <= 10;){
   //... Statements
   counter++;
}

// Infinite loop
for(;true;);

Note: The condition check happens before the statements in the loop are executed. In addition, the increment statement happens after all the statements, a fact that many may overlook.

Exercises

// 1.

int a = 0;
for(int i = 0; i < 10; i++) {
    a += 10;
}

// what is the value of 'a': ___ ?




// 2.

int b = 0;
for (b = 1; b < 20; b++) {
    b = b + b;
}

// what is the value of 'b': ___ ?



// 3.
int c = 7;
for (; c > 15; c++) {
    c++;
}

// what is the value of 'c': ___ ?