Help fix this problem in C#

Question

Write a method “SumNum” that accepts an integer parameter and returns the sum of all the integers from 1 up to the number passed as an argument. For example, if you pass 20 as an argument, the method will return the sum of 1, 2, 3, 4, . . . 20 which is 210.

namespace Lab6
{
internal class Program
{
static int SumNum(int num)
{
for (int i = 0; i <= num; i++)
{
return i;
}
}
static void Main(string[] args)
{
int Sum1 = SumNum(20);
Console.WriteLine(Sum1);
}

}  

}
It says Error CS0161: 'Program.SumNum(int)': not all code paths return a value (CS0161) (Lab6) and Warning CS0162: Unreachable code detected (CS0162) (Lab6)

Answer 1

In C# all functions must return a value through all possible code paths.

   static int SumNum(int num)  
   {  
      for (int i = 0; i <= num; i++)  
      {  
         return i;  
      }  
   }  

Notice in your function, once indented, that you are not returning a value from the function if num is less than 0. The for loop will never execute the statement inside it and therefore code continues after the loop. Since there is no return then the compiler fails. To fix that return a value for when num is less than 0.

Also note that your code isn't actually summing up anything. It is returning the first time through the loop so the result will always be 0. You should create an accumulator local variable. Each time through the loop add the current loop value (i) to the local variable. Once the loop is complete then return the accumulated value. Interestingly, this would resolve the compiler error as well since you would initialize your accumulator to 0.