Help with Debugging

[Nicholasbardy]

I just started writing in C. So any help is appreciated. This is a program to find all the pairs of numbers that add to give the inputted number

// Main Function
void _main(int a1)
{
	

	// Find All Numbers where int a + int b = a1

	
		
		// Start by finding the size of array needed
		// Odd integers have (a-1)/2 values
		// Even have a/2 values

		if ( ( a1%2 ) == 1 ) 
		{
		     int adders = ((a1 - 1) / 2);
		}
		else 
		{
		     int adders = (a1 / 2);	
		}
		
	

		// Iniate array and store values
	
		int adderarray[adders][2];
			
		
		for (int i;i <= adders; i++)
		{
		     adderarray[(i-1)][0] = i;
					
		     adderarray[(i-1)][1] = (a1 - i);
		}
				

}

I get error:

'adders' undeclared (first use in this function).

So when the array 'adderarray' is declared the variable adders doesn't exsist, right? But it should have a value from the If/else statement?

I'm trying to figure out why it is wrong not just what is wrong. Thanks for helping.

[tabstop]

Variables have scope. To figure out the lifetime of a variable, find its declaration, move backward to the first open-curly, and then find the matching close-curly. That matching close-curly is the end of the road for that variable. So your first variable adders ONLY exists in the "then" part of the if statement, and the second variable adders ONLY exists in the "else" part. By the time we get below, both adders variables have died.

[Nicholasbardy]

Changed to

if ( ( a1%2 ) == 1 ) 
     int adders;
		{
		     adders = ((a1 - 1) / 2);
		}
		else 
		{
		     adders = (a1 / 2);	
		}

[matsp]

That is only valid in C99 - C89 would complain about declaring variables in that place.

--
Mats

[Elysia]

Main must return int, not void.
Main shall not be defined as _main, but rather main.
And lastly, main shall take no arguments or it shall take
int main(int, char**)
So says the standard.

Adders should be defined before the if statement.
Also remember that the way you create your array is also C99.