Question

C Program:

6.31 (Palindromes) A palindrome is a string that's spelled the same way forward and backward.
Some examples of palindromes are:

"radar"
"able was i ere i saw elba"

and, if you ignore blanks:

"a man a plan a canal panama"

Write a recursive function testPalindrome that returns 1 if the string stored in the array is
a palindrome and 0 otherwise. The function should ignore spaces and punctuation in the string.
Use the function in a complete program which first asks the user for the size of the string
and then asks for the string itself. Do not change the original string in your testPalindrome
function. You can assume that capital and smaller case letters are not equal.

Input Validation: if the user enters a value less than or equal to zero for string size, print
an error message and exit.

inputs:

27, a·man·a·plan·a·canal·panama

Output: Enter the size of your string: Enter your string to check if it is a palindrome: "a man a plan a canal panama" is a palindrome.

Answer 1

#include <stdio.h>
#include<string.h>

int testPalindrome(char str[]){
  
// initializing lower and upper with start point and end point of the string
int lower = 0;
int upper = strlen(str) - 1;
  
// checking the string till lower is smaller than and equal to upper
while (lower <= upper) {
// if there is any other character than lowercase or uppercase alphabet, increment the lower index
if (!(str[lower] >= 'a' && str[lower] <= 'z') && !(str[lower] >= 'A' && str[lower] <= 'Z'))
lower++;
// if there is any other character than lowercase or uppercase alphabet, decrement the upper index
else if (!(str[upper] >= 'a' && str[upper] <= 'z') && !(str[upper] >= 'A' && str[upper] <= 'Z'))
upper--;
// if alphabets at lower and upper index are equal, increment the lower index and decrement the upper index
else if (str[lower] == str[upper])
lower++, upper--;
// if alphabets at lower and upper index are not equal, return 0, as the string is not palindrome
else
return 0;
}
  
return 1;
}

int main()
{
int size;

printf("Enter the size of the string: \n");
scanf("%d",&size);

char str[50];
char temp;

// checking if the size of the string is negative
if(size<=0){
printf("Error! Size must be a positive number.\n");
}
else{
printf("Enter your string to check if it is a palindrome: ");
scanf("%c",&temp); // temp statement to clear buffer
   scanf("%[^\n]",str); //[^\n] considers the spaces also in the string, and stops reading input, if it encounters new line.
  
  
// calling and checking if the given string is palindrome or not
if(testPalindrome(str)){
printf("\n%s is a palindrome", str);
}
else{
printf("\n%s is not a palindrome", str);
}
}

return 0;
}