i've a question about this code i'm writing for an exercise. I've to check if a string is palindrome. I can't change the declaration of the function.The function only return 1 when all the letters are the same (like "aaaa") but if i charge the sentence with other palindrome (like "anna") the function return me 0 , i can't figure out why this appening.Thank you!
char* cargar (char*);
int pali (char*);
int main()
{
char*texto=NULL;
texto=cargar(texto);
int res=pali(texto);
if(res==1){printf("\nPalindrome");}
else printf("\nNot palindrome");
return 0;
}
char* cargar (char*texto)
{
char letra;
int i=0;
texto=malloc(sizeof(char));
letra=getche();
*(texto+i)=letra;
while(letra!='\r'){
i++;
texto=realloc(texto,(i+1)*sizeof(char));
letra=getche();
*(texto+i)=letra;}
*(texto+i)='\0';
return texto;
}
int pali (char* texto)
{
int i;
for(i=0;*(texto+i)!='\0';i++){
}i--;
if(i==0||i==1){return 1;}
if(*texto==*(texto+i)){
return pali(++texto);
}
else return 0;
}
Your function to determine whether a string is a palindrome is not well thought out.
Let's say you have a string s
of length l
. The characters in the string are laid out as:
Indices: 0 1 2 3 l-4 l-3 l-2 l-1
+----+----+----+----+- ... -+----+----+----+----+
| | | | | ... | | | | |
+----+----+----+----+- ... -+----+----+----+----+
If the string is a palindrome,
s[0] = s[l-1]
s[1] = s[l-2]
...
You can stop checking when the index of the LHS is greater or equal to the index of the RHS.
To translate that into code,
int is_palindrome(char const* s)
{
size_t len = strlen(s);
if ( len == 0 ) // An empty string a palindrome
{
return 1;
}
size_t i = 0;
size_t j = len-1;
for ( ; i < j; ++i, --j )
{
if ( s[i] != s[j] )
{
// the string is not a palindrome.
return 0;
}
}
// If we don't return from inside the for loop,
// the string is a palindrome.
return 1;
}