Nested switch leads to an infinite loop - c

Question

In the following program, I need to change the initial and final characters to their respective characters as mentioned below in case but this is giving me an infinite loop. What should I do to fix it?
int main(void)
{
char state ='t';
char word[20]="aaabbccaaaaccbbb";
int initiallength = strlen(word)-1; strcat(word,"a");
while(strlen(word)-1 >initiallength)
{
switch(state)
{
case 't':
switch(word[strlen(word)-1])
{
case 'a':
word[strlen(word)-1]='b'; break;
case 'b':
word[strlen(word)-1]='c'; break;
case 'c':
word[strlen(word)-1]='d'; break;
case 'd':
word[strlen(word)-1]='\0'; break;
}
switch(word[0])
{
case 'a':
word[0]='b'; break;
case 'b':
word[0]='c'; break;
case 'c':
word[0]='d'; break;
case 'd':
word[0]='\0'; break;
}
}
}
}

Answer 1

If I understand correctly what you want to do is swap the first and last characters in the given string. If that's the case first your code is way too complicated and second the reason you're getting an infinite loop is because the condition strlen(word)-1 >initiallength is always true.

Answer 2

Test if word is empty
int main(void){
char state ='t';
char word[20]="aaabbccaaaaccbbb";
int initiallength = strlen(word)-1;
strcat(word,"a");
while(strlen(word)-1 >initiallength && strlen(word) >= 0){
printf("%d %d\n", strlen(word)-1, initiallength);
printf("%d len %s\n", strlen(word), word);
switch(state){
case 't':
switch(word[strlen(word)-1]){
case 'a':
case 'b':
case 'c':
word[strlen(word)-1]++;
break;
case 'd':
word[strlen(word)-1] = '\0';
break;
}
switch(word[0]){
case 'a':
case 'b':
case 'c':
word[0]++;
break;
case 'd':
word[0] = '\0';
break;
}
}
}
}