Our teacher gave us homework to check for palindrome of a word using data structure "Stack".
Below is the code which I have written for the following problem: -
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# include <stdbool.h>
struct Stack
{
int top;
int capacity;
char *array;
};
void push(struct Stack stack, char a) //Push function.
{
stack.array[++stack.top] = a; //Helps to push charater to a stack.
}
char pop(struct Stack stack) //Pop function.
{
return stack.array[stack.top--]; //Helps to pop character from a stack.
}
int main(void)
{
struct Stack original; //Original stack where the "Original" word will be pushed.
original.top = -1;
original.capacity = 10;
original.array = calloc(original.capacity, sizeof(char));
struct Stack checker; //Another stack that "Checks" whether the word is palindrome or not.
checker.top = -1;
checker.capacity = 10;
checker.array = calloc(checker.capacity, sizeof(char));
while(getchar()!='\0') //Getting all the characters from the stdin buffer and pushing it into "Original" stack.
{
push(original, getchar());
}
while(original.top != -1)
{
push(checker,pop(original)); //Popping from "Original" stack and pushing it to "Checker" stack.
}
while(checker.top != -1)
{
original.top = checker.top;
if(original.array[original.top] != checker.array[checker.top]) //Checking every character in the stack if it is excatly same or not.
{
printf("It is not a palindrome.\n");
return EXIT_SUCCESS;
}
else
{
checker.top = checker.top - 1;
}
}
if(checker.top == -1)
{
printf("It is a palindrome.\n");
}
return 0;
}
Howsoever I am getting problem in the following line: -
while(getchar()!='\0') //Getting all the characters from the stdin buffer and pushing it into "Original" stack.
{
push(original, getchar());
}
The following loop is running infinitely. My purpose of adding the following line is that I want to add individual characters from stdin buffer and push it in the original stack until it encounters '\0'.
What have I done wrong here? Is it illegal to do it this way?
Addendum: -
Sample Input 1: - civic
Expected Output: - It is a palindrome.
Sample Input 2: - madama
Expected Output: - It is not a palindrome.
P.S.
The following code: -
while(getchar()!='\0') //Getting all the characters from the stdin buffer and pushing it into "Original" stack.
{
push(original, getchar());
}
has now been replaced with: -
int c;
int i = 0;
while ( i < original.capacity && ( c = getchar() ) != EOF && c != '\n' )
{
push(original, c );
++i;
}
And is now working perfectly, howsoever now, for every word, my code is giving the output: -
It is a palindrome.
Where have I applied the concept of stack incorrectly?
This loop
while(getchar()!='\0') //Getting all the characters from the stdin buffer and pushing it into "Original" stack.
{
push(original, getchar());
}
is in any case wrong because it reads characters twice: in the condition of the loop and within the body of the loop.
And you have explicitly to enter 0 using for example keypad.
What you need is the following
int c;
int i = 0;
while ( i < original.capacity && ( c = getchar() ) != EOF && c != '\n' )
{
push(original, c );
++i;
}
Also there is one more problem. These functions deal with a copy of the passed arguments.
void push(struct Stack stack, char a) //Push function.
{
stack.array[++stack.top] = a; //Helps to push charater to a stack.
}
char pop(struct Stack stack) //Pop function.
{
return stack.array[stack.top--]; //Helps to pop character from a stack.
}
You have to declare them like
void push(struct Stack *stack, char a) //Push function.
{
stack-?array[++stack->top] = a; //Helps to push charater to a stack.
}
char pop(struct Stack *stack) //Pop function.
{
return stack->array[stack->top--]; //Helps to pop character from a stack.
}
That is to pass the original stack by reference through pointer.
And call these functions as for example
push( &original, c );
Otherwise the data member top will not be changed.
Here is your updated program
# include <stdio.h>
# include <stdlib.h>
struct Stack
{
int top;
int capacity;
char *array;
};
void push(struct Stack *stack, char a) //Push function.
{
stack->array[++stack->top] = a; //Helps to push charater to a stack.
}
char pop(struct Stack *stack) //Pop function.
{
return stack->array[stack->top--]; //Helps to pop character from a stack.
}
int main(void)
{
struct Stack original; //Original stack where the "Original" word will be pushed.
original.top = -1;
original.capacity = 10;
original.array = calloc(original.capacity, sizeof(char));
struct Stack checker; //Another stack that "Checks" whether the word is palindrome or not.
checker.top = -1;
checker.capacity = 10;
checker.array = calloc(checker.capacity, sizeof(char));
int c;
int i = 0;
while ( i < original.capacity && ( c = getchar() ) != EOF && c != '\n' )
{
push( &original, c );
++i;
}
while(original.top != -1)
{
push(&checker,pop(&original)); //Popping from "Original" stack and pushing it to "Checker" stack.
}
while(checker.top != -1)
{
original.top = checker.top;
if(original.array[original.top] != checker.array[checker.top]) //Checking every character in the stack if it is excatly same or not.
{
printf("It is not a palindrome.\n");
return EXIT_SUCCESS;
}
else
{
checker.top = checker.top - 1;
}
}
if(checker.top == -1)
{
printf("It is a palindrome.\n");
}
return 0;
}
Take into account that these headers
#include <string.h>
#include <stdbool.h>
are redundant.