what is yield in c#.

To understand Yield you must understand the difference between return and yield return. Lets see the with example

static int SimpleReturn()  
{  
    return 1;  
    return 2;  
    return 3;  
}  
static void Main(string[] args)  
{  
    Console.WriteLine(SimpleReturn());  
    Console.WriteLine(SimpleReturn());  
    Console.WriteLine(SimpleReturn());  
    Console.WriteLine(SimpleReturn());  
}  
 
Output:

1
1
1
1

In above example int SimpleReturn function three returns are mentioned but no matter how many times this function is called from anywhere, here from main the function will always return first value i.e 1.

Yield statement in C#

Example to demonstrate yield statement:

static IEnumerable YieldReturn()  
{  
    yield return 1;  
    yield return 2;  
    yield return 3;  
}  
static void Main(string[] args)  
{  
    foreach (int i in YieldReturn())  
    {  
        Console.WriteLine(i);  
    }  
}  

Output:

1
2
3

The only difference between yield and return is whenever yield statement is encountered in a function, the execution of function is suspended and a value is send back to the caller but because of yield whenever the function is called again, the execution of function begin where it left off previously. When resumed, the function continues execution immediately after the last yield run. Thus yield allows a function to produce a series of values over time. The only requirement for yield return statement is that the function containing yield should return an IEnumerable and no matter from where that function is called it should be called from an iteration block i.e foreach statement.