Merge pull request #19 from v-community/add-if-statement-md

example: conditional statements like if, else, else if, for and while.

.gitignore

@@ -6,6 +6,7 @@
 a.out.tmp.c
 *.vrepl.v
 *.vrepl
+.vrepl_temp
 
 .DS_Store
 data/.DS_Store

examples/conditional_statements/conditional_statements.md

@@ -0,0 +1,141 @@
+# Conditional Statements
+
+## If statement
+
+An `if` statement is a programming conditional statement that, if proved true, performs a function or displays information. Below is a general example of an if statement in V:
+
+```go
+john_height := 100
+maria_height := 178
+
+if john_height < maria_height {
+	println('$john_height < $maria_height')
+} else {
+	println('$john_height > $maria_height')
+}
+```
+
+The `if...else` statement executes two different codes depending upon whether the test expression is `true` or `false`. Sometimes, a choice has to be made from more than 2 possibilities. The `if...else if...else` ladder allows you to check between multiple test expressions and execute different statements.
+
+```go
+tom_age := 20
+ashia_age := 38
+
+if tom_age < ashia_age {
+	println('$tom_age < $ashia_age')
+} else if tom_age > ashia_age {
+	println('$tom_age > $ashia_age')
+} else {
+	println('$tom_age == $ashia_age')
+}
+```
+
+It's possible to include an `if...else` statement inside the body of another `if...else` statement.
+
+```go
+tom_age := 20
+ashia_age := 38
+
+if tom_age < ashia_age {
+  if tom_age < 18 {
+	println('tom_age < 18 and younger than Ashia.')
+  } else {
+	println('tom_age > 18 and older than Ashia.')
+  }
+} else {
+	println('$tom_age == $ashia_age')
+	println('Tom and Ashia have the same age.')
+}
+```
+
+There are no parentheses surrounding the condition, and the braces are always required.
+
+`if` can also be used as an expression:
+
+```go
+tom_age := 20
+ashia_age := 38
+
+s := if tom_age < ashia_age {
+	'Tom is the youngest'
+} else {
+	'Ashia is the youngest'
+}
+
+print(s) // 'Tom is the youngest'
+```
+
+## Exercises
+
+1. Write a V program to accept two integers and check whether they are equal or not.
+2. Write a V program to check whether a given number is even or odd.
+3. Write a V program to check whether a given number is positive or negative.
+4. Write a V program to find whether a given year is a leap year or not.
+
+## For
+
+`for` loops offer a quick and easy way to do something repeatedly. They're handy, if you want to run the same code over and over again, each time with a different value. You can think of a loop as a computerized version of the game where you tell someone to take X steps in one direction then Y steps in another; for example, the idea "Go five steps to the east" could be expressed this way as a loop:
+
+```go
+for i := 0; i < 5; i++ {
+  println('Walking one step');
+}
+```
+
+V has the `for` looping construct and the loop can be written in different ways:
+
+1. `in` operator
+
+```go
+ages := [18, 25, 32, 43, 50]
+
+for age in ages {
+	println(age)
+}
+```
+
+Note, that the value is read-only.
+
+2. `while` loop form
+
+A `while` loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. There are no parentheses surrounding the condition, and the braces are always required.
+
+```go
+mut factorial := 1
+mut counter := 1
+
+for {
+	counter++
+	factorial=factorial*counter
+
+	if counter > 5 {
+		print(factorial)
+		break
+	}
+}
+println(counter) // "120"
+```
+
+3. `for` with the traditional C style
+
+```go
+mut factorial := 1
+mut counter := 1
+
+for i := 0; i < 5; i++ {
+	factorial=factorial*counter
+	if i == 6 {
+		print(factorial)
+		continue
+	}
+	println(i)
+}
+```
+
+## Exercises
+
+1. Write a V program to display the first 10 natural numbers.
+2. Write a V program to find the sum of first 10 natural numbers.
+3. Write a V program to display n terms of natural number and their sum.
+4. Write a V program to read 10 numbers from keyboard and find their sum and average.
+5. Write a V program to display the cube of the number upto given an integer.