74 lines
2.7 KiB
Markdown
74 lines
2.7 KiB
Markdown
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---
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title: For Loop
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---
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# For Loop
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The `for` loop gives you a compact way to iterate over a range of values.
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A basic `for` statement has three parts: a variable initialization, a boolean expression, and an increment expression.
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```java
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for (variable initialization; boolean expression; increment expression)
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{
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// Statements
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}
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```
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* `initialization` - Initializes the loop and is executed just once, at the beginning.
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You can initialize more than one variable of the same type in the first part of the basic `for` loop declaration; each initialization must be separated by a comma.
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* `expression` - Evaluated at the beginning of each iteration. If the `expression` evaluates to `true`, `Statements` will get executed.
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* `increment` - Invoked after each iteration through the loop. You can increase/decrease the value of variables here. Be sure the increment is working towards the expression value, to avoid an infinite loop.
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A common way the `for` loop is used is if you need to iterate your code a specific number of times. For example, if you wanted to output the numbers 0-10, you would initialize the variable for your counter to 0, then check if the value is less than 10, and add one to the counter after every iteration.
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Notice that you would check if the value is less than 10, not less than or equal to 10, since you are starting your counter at 0.
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```java
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for (int iter_For = 0; iter_For < 10; iter_For++)
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{
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System.out.print(iter_For + " ");
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// Iterated 10 times, iter_For 0,1,2...9
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}
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System.out.println("iter_For Value: " + iter_For);
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```
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Note: It is also acceptable to declare a variable within the for loop as a single statement.
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```java
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for (int iter_For = 0; iter_For < 10; iter_For++)
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{
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System.out.print (iter_For + " ");
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// Iterated 10 times, iter_For 0,1,2...9
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}
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```
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Output:
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```
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0 1 2 3 4 5 6 7 8 9
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iter_For Value: 10
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```
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Another example of a for loop that adds the first 50 numbers would be like this.
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i++ means i = i+1.
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```java
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int addUntil = 50;
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int sum 0;
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for (int i = 1; i <= addUntil; i++)
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{
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sum+=i
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}
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System.out.println("The sum of the first 50 numbers is: " + 50);
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```
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 <a href='https://repl.it/CJYr/0' target='_blank' rel='nofollow'>Run Code</a>
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### Extras
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You cannot use a number (old C-style language construct) or anything that does not evaluate to a boolean value as a condition for an if statement or looping construct. You can't, for example, say if(x), unless x is a boolean variable.
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Also, it is important to keep in mind that the boolean expression must, at some point, evaluate to true. Otherwise, your program will be stuck in an infinite loop.
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