Palindrome Algorithm in C .

Hello to all. I have some confusion here.....

My code :

Code:

---


#include<stdio.h>
#include<string.h>
#include<stdbool.h>
#include <ctype.h>
#define STR_LEN 50
int is_palindrome( const char []);
void read_line(char [] , int );
int main( void )
{
    char str[STR_LEN + 1] = {'\0'};
   
    for(;;) {
   
    printf("\n Enter a word (Enter a single letter to terminate) : \n");
    read_line(str , STR_LEN ); 
   
    if(strlen(str) < 2)
    break;
   
    if( is_palindrome( str ) )
    printf(" Word %s is  palindrome " , str);
   
    else
    printf(" Word %s is not palindrome " , str);
}
       
        return 0;
}
void read_line(char str[] , int n)
{
    int ch , i=0;
    while( (ch = getchar()) != '\n' ) {
       
        if( !isalpha(ch)) {
        printf(" \n *Rejected* '%c' is not a letter " , ch);
        continue;
            }   
       
        if(i < n )
        str[i++] = ch;
    }
       
        str[i] = '\0';
}

int is_palindrome(const char* str) {
       
    const char* last = str + strlen(str) - 1;
    while (str < last) {
        if (*str++ != *last--) return 0;
    }           
 
    return 1;
}

---

I have a basic question not about the code but about the algorithm which code uses in order to find a palindrome.

How many pass algorithm does? 1 + 1/2 or 2?

> How many pass algorithm does? 1 + 1/2 or 2?
How about adding some code to find out?

Code:

---

int is_palindrome(const char* str) {
    int numPasses = 0;
    const char* last = str + strlen(str) - 1;
    while (str < last) {
        numPasses++;
        if (*str++ != *last--) return 0;
    }           
 
    return 1;
}

---

Printing numPasses is an exercise for you.

I meant the passes from complexity perspective. For example....

str pointer will pass 1 and 1/2 times the list (the word) one time when we read the word and one half time when we look for the characters ....
last pointer will pass 1/2 times the list (the word). My question (if it makes sense) : The considerable pass from this process are 1 + 1/2 or 2?

I have read that if we have this list : 0 1 2 3 4 5 6 7 8 9 10

we need n/2 pass in order to find some element . The total pass is n/2 or n/2 + n/2 ?

If you've got one process step which takes n iterations, followed by another which takes n as well, then the overall order of the computation is still n.