'If' statement

The 'if' statement determines whether the condition is true or not. If condition is true then the 'if' block is executed otherwise, control skips the 'if' block.

if block
if-else block
if else-if ladder
nested if

Syntax of 'if':

if condition  
 {  
             //block statements;  
} 

In the above syntax, if the condition is true then the block statements are executed otherwise it skips the block.

For Example:

fn main()  
  
 let a=1;  
 if a==1  
  {  
      println!("a is equal to 1");  
   }  

a is equal to 1

In this example, value of a is equal to 1. Therefore, condition given in 'if' is true and the string passed as a parameter to the println! is displayed on the console.

"if-else"

If the condition is true then 'if' block is executed and the statements inside the 'else' block are skipped. If the condition is false then 'else' block is executed and the statements inside the 'if' block are skipped.

Syntax of "if-else"

 if condition  
{  
   //block statements  
}  
else  
{  
    //block statements  
 }  

fn main()  
{  
  let a=3;  
  let b=4;  
  if a>b  
  {  
     println!("a is greater than b");  
  }  
  else  
   {  
     println!("a is smaller than b");   
   }  
}  

a is smaller than b

In this example, value of a is equal to 3 and value of a is less than the value of b. Therefore, else block is executed and prints "a is smaller than b" on the screen.

else-if

When you want to check the multiple conditions, then 'else-if' statement is used.

Syntax of else-if

 if condition 1  
{  
  //block statements  
}  
else if condition 2  
{  
  //block statements  
}   
.  
.  
else{  
//block statements  
}  

In the above syntax, Rust executes the block for the first true condition and once it finds the first true condition then it will not execute the rest of the blocks.

fn main()  
  
 let num= -5;  
 if num>0  
 {  
   println!("number is greater than 0");  
 }  
 else if num< 0  
 {  
   println!("number is less than 0 ");  
 }  
 else  
 {  
   println!("number is not equal to 0");  
 }  

number is less than 0

In this example, value of num is equal to -5 and num is less than 0. Therefore, else if block is executed.

Nested if-else

When an if-else statement is present inside the body of another if or else block then it is known as nested if-else.

Syntax of Nested if-else

 if condition 1  
{  
   // block statements  
   if condition 2  
{  
      //block statements  
}  
else  
{  
    //block statements  
}  
}  
else  
{  
   //block statements  
}  

fn main()  
  
 let a=5;  
 let b=6;  
 if a!=b  
 {  
   if a>b  
   {  
     println!("a is greater than b");  
   }  
   else  
    {  
      println!("a is less than b");  
    }  
 }  
  
 else  
{  
      println!("a is equal to b");  
 }  

a is less than b

In this example, value of a is not equal to b. So, control goes inside the 'if' block and the value of a is less than b. Therefore, 'else' block is executed which is present inside the 'if' block.