What the string?!

[PunchOut]

why does lower[] print lower and upper case letters?

probably right in front of my face!

#include <stdio.h>

void alpha(char upper[26], char lower[26]);

main()  
{
	char upper[26], lower[26];
	alpha(upper, lower);
	printf("%s\n%s\n", upper, lower);

}

void alpha(char u[], char l[])
{
	int i;
        char X = 65;
        char x = 97;

        for(i = 0; i < 26; i++) 
	{
                u[i] = X++;
                l[i] = x++;
        }
}

[rags_to_riches]

You need to have room for 27 chars in your arrays...you need room for the null terminator, and you need to add it.

[cpjust]

BTW, I hope you don't use this technique in production code when in a company, since it isn't portable (i.e. it only works on ASCII platforms).
But if you're doing this just for school then it would be a lot more readable if you replace 65 with 'A' and 97 with 'a' so people don't have to look up an ASCII chart to see if it's right or not.