如何在字符串中写出终止符(即等于0的值)

怎么在字符串中写出终止符(即等于0的值)?
char str[256] = "abcdef";

我想把他变成这样:
str[0] = 'a';
str[1] = 'b';
str[2] = 'c';
str[3] = 0;
str[4] = 'd';
str[5] = 'e';
str[6] = 'f';
str[7] = 0;

那么这个str初始化的字符串该怎么写????

------解决方案--------------------
char str[256] = {'1','2','3','\0','4','5','6','\0'};