Rust Program to Multiply Two Int & Float Numbers

Rust-Programs

In this example, we will learn Rust Program to Multiply Two Int & Float Numbers entered by the user. We will calculate the multiplication results and print them on the screen.

To understand this example, you should have knowledge of the following Rust programming topics:

  • Rust Variables, Constants and Literals
  • Rust Data Types
  • Rust Input Output (I/O)
  • Rust Programming Operators

1. Rust Program to Multiply Two int Numbers enetered by User

In this example, we are taking two integer numbers entered by the user and performing a mutiplication of these numbers.

use std::io;
fn main() {
          // User will enter first number
          println!("Input First number ? ");
          let mut var1 = String::new();
          io::stdin().read_line(&mut var1).expect("Unable to read entered data");

          // User will enter Second number
          println!("Input second number ? ");
          let mut var2 = String::new();
          io::stdin().read_line(&mut var2).expect("Unable to read entered data");

          // Converting string to integer
          let a: i32 = var1.trim().parse().ok().expect("Program only processes numbers, Enter number");
          let b: i32 = var2.trim().parse().ok().expect("Program only processes numbers, Enter number");

          // Output of basic operations

          println!("Multiply is: {}", a * b);

}

Output

Input First number ? 3
Input second number ? 5

Multiply is: 15

2. Rust Program to Multiply Two Float Numbers enetered by User 

use std::io;
fn main() {
          // User will enter first number
          println!("Input First number ? ");
          let mut input1 = String::new();
          io::stdin().read_line(&mut input1).expect("Unable to read entered data");

          // User will enter Second number
          println!("Input second number ? ");
          let mut input2 = String::new();
          io::stdin().read_line(&mut input2).expect("Unable to read entered data");

          // Converting string to float
          let a: f32 = input1.trim().parse().ok().expect("Program only processes numbers, Enter number");
          let b: f32 = input2.trim().parse().ok().expect("Program only processes numbers, Enter number");

          // Output of basic operations

          println!("Multiply is: {}", a * b);

}

Output

$rustc -o main *.rs
$main
Input First number ? 12.5
Input second number ? 3.5
Multiply is: 43.75

How this works?

1. std::io module:

The first line of the program is to include the std::io module of Rust. This module has a lot of functionality, but its main use is to provide support for reading and writing traits.

2. String::new() and mut:

Then the next line is to declare a mutable variable var1 and it will be of type string as we are doing a String::new() for this. We are declaring it as mutable because we will be using this to save the input from the user. If we don’t add the mut keyword then this will be throw error when we will try to assign it a value later in the program.

3. read_line() function :

Next we are making use of the read_line() method from the std::io module.The read_line() method takes a &mut String as an argument, which means reference of a mutable String. So it means when the user will enter an input then the read_line() function will read that input and put that into a string variable for which we are passing its reference.

4. expect() function :

The expect() function which is used for error handling in Rust.This is not mandatory to call but in Rust, we prefer to call this because if we don’t call this then we will be flagged by the compiler with a warning. There is the possibility that the read_line() function can fail due to any reason other than to avoid the program crashing without any notification we add the expect call. What it does is, display the message we pass to it on screen in case there is an error reported.

5. Taking Input from User

We are taking the input of the second number in var2 and for var2 also we are doing exactly the same as what we did for var1. Now we got the 2 numbers input read in the form of a String, but we expect them to be numbered. so we will need to convert them to numbers before we perform the multiplication. Before we apply the conversion, we will need to make sure the String that we are going to convert does not have any special characters in it.This is important in Rust because when the user will enter the number and presses enter, it may add a \n new line to the String that we will get from the read_line() method. So to make sure we get the correct value we will make sure of the trim() method. The trim() method on the strings eliminates any special character at the beginning and end of the data and will leave only the number part.

6. Convert String input to Numeric Type

Since we have the number in a string now, so our next step is to convert it to a numeric data type. In Rust, we have different formats to save numeric values like i32,i64,u32,u64 which means integer 32 bit, integer 64 bit, etc.
We are making use of the parse() method which will help us to convert our string data to number format. The parse() method will give us the numbers in i32 format here.

7. Perform multiplication

Once we have the numbers in variables a and b then the only job left is to perform the multiplication. We are doing the simple multiply by using the * operator. Finally printing the result by using println!().

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