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Rust – Constants
  • Last Updated : 31 Mar, 2021

Constants are the value that can not be changed after assigning them. If we created a constant, then there is no way of changing its value. The keyword for declaring constant is const. In Rust, constants must be explicitly typed.  The below syntax is used to initialize a constant value:

Syntax :

const VARIABLE_NAME:dataType = value;

Now let’s check out some examples for the same.

Example 1 :

Rust






fn main() {
    
   // Declare an integer constant
   const MARKS:i32 = 100;
    
   // Declare a float constant
   const PI:f32 = 3.14;  
    
   // Declare a string constant
   const NAME:&str = "GFG";
  
   // display constants
   println!("MARKS {}",MARKS);  
   println!("PI {}",PI);     
   println!("NAME {}",NAME);
}

Output:

MARKS 100
PI 3.14
NAME GFG

Example 2

Rust




fn main() {
    
  // Declare an integer constant
   const GFG:i32 = 100;
  
  // declaring another constant with same name
  const GFG:i32 = 200;
  
  // printing the value
  println!("{}",GFG);
}

This will produce an error :




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