Rust Tutorial :
from tutorialspoint.com

Defining a Function
function definition specifies what and how a specific task would be done
the function body contains code that should be executed by the function
rules for naming a function are similar to that of a variable
functions are defined using the fn keyword
syntax 
fn function_name(param1,param2..paramN) {
   // function body
}
simple function example 
fn fn_hello(){
   println!("hello from function fn_hello ");
}
Invoking a Function
example 
fn main(){
   //calling a function
   fn_hello();
}
//Defining a function
fn fn_hello(){
   println!("hello from function fn_hello ");
}
Returning Value from a Function
with return statement
syntax 
fn function_name() -> return_type {
   // statements
   return value;
}
without return statement
syntax 
fn function_name() -> return_type {
   value // no semicolon means this value is returned
}
Function with Parameters
Pass by Value
when a method is invoked, a new storage location is created for each value parameter
the values of the actual parameters are copied into new locations
the changes made to the parameter inside the invoked method have no effect on the argument 
fn main(){
   let no:i32 = 5;
   mutate_no_to_zero(no);
   println!("The value of no is:{}",no);
}

fn mutate_no_to_zero(mut param_no: i32) {
   param_no = param_no*0;
   println!("param_no value is :{}",param_no);
}
output 
param_no value is :0
The value of no is:5
Pass by Reference
passing parameters by reference represent the same memory location as the actual supplied parameters
parameter values can be passed by reference by prefixing the variable name with an & 
fn main() {
   let mut no:i32 = 5;
   mutate_no_to_zero(&mut no);
   println!("The value of no is:{}",no);
}
fn mutate_no_to_zero(param_no:&mut i32){
   *param_no = 0; //dereference the pointer
}
output 
The value of no is 0
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