C program to check String is Palindrome or not using Stack

C program to check String is Palindrome or not using Stack - Source code

int top = -1, front = 0;
int stack[MAX];
 
void push(char);
void pop();
 
void main()
{
    int i, c;
    char s[MAX], b;
    while (1)
    {
        printf("1-enter string\n2-exit\n");
        printf("enter your choice\n");
        scanf("%d", &c);
        switch (c)
        {
        case 1:
            printf("Enter the String\n");
            scanf("%s", s);
            for (i = 0;s[i] != '\0';i++)
            {
                b = s[i];
                push(b);
            }
            for (i = 0;i < (strlen(s) / 2);i++)
            {
                if (stack[top] == stack[front])
                {
                    pop();
                    front++;
                }
                else
                {
                    printf("%s is not a palindrome\n", s);
                    break;
                }
            }
            if ((strlen(s) / 2)  ==  front)
                printf("%s is palindrome\n",  s);
            front  =  0;
            top  =  -1;
            break;
        case 2:
            exit(0);
        default:
            printf("Please enter correct choice\n");
        }
    }
}
 
/* to push a character into stack */
void push(char a)
{
    top++;
    stack[top]  =  a;
}
 
/* to delete an element in stack */
void pop()
{
    top--;
}

Program Output

1-enter string
2-exit
enter your choice
1
Enter the String
madam
madam is palindrome
1-enter string
2-exit
enter your choice
1
Enter the String
abbbcbbba
abbbcbbba is palindrome
1-enter string
2-exit
enter your choice
compscibits
Enter the String
compscibits is not a palindrome
1-enter string
2-exit
enter your choice

Program Explanation

1. Take a string as input and store it in the array s[].

2. Load each character of the array s[] into the array stack[] using a for loop.

3. Use variables front and top to represent the last and top element of the array stack[].

4. Using for loop compare the top and last element of the array stack[]. If they are equal, then delete the top element, increment the variable front by 1 and compare again.

5. If they are not equal, then print the output as “It is not a palindrome”.

6. Compare the elements in the steps 4 and 5 upto the middle element of the array stack[].

7. If every characters of the array is equal, then it is a palindrome.