if statement with char is not working in C

Question

For the most part everything is working and it's able to build error free. However when I try to run it, it seems to crash. To be more specific, whenever I start my code and press 'a' or 'b', the program keeps crashing. Can someone tell me how to fix that?

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

int top=-1;
int word;


char stack_string[100];
void push(char word);
char pop(void);
int main()
{
    char input;
    char str[100];
    int i;
    printf("press [a] for palindrome check, [b] for string reversal:");
    scanf("%s", input);

    if (input == 'b'){
        printf("Input a string: ");
        scanf("%[^\n]s", str);
        for(i=0;i<strlen(str);i++)
            push(str[i]);
        for(i=0;i<strlen(str);i++)
            str[i]=pop();
        printf("Reversed String is: %s\n",str);
    }
    else if(input == 'a'){
        char str[100];
        int count = 0;
        printf("Input a string: ");
        scanf("%[^\n]s", str);

        for (i = 0; i < strlen(str); i++)
        {
            push(str[i]);
        }

        for (i = 0; i < strlen(str); i++)
        {
            if (str[i]==pop())
            count++;
        }

        if (count == strlen(str))
            printf("%s is a palindrome\n", str);
        else
            printf("%s is not a palindrome\n", str);

    }

    return 0;
}

void push(char word)
{
    top=top+1;
    stack_string[top]=word;
}

 char pop()
{
    word = stack_string[top];
    top=top-1;
    return word;
}

Answer 1

main problem is you are reading a string but comparing it to a single char

that's why if condition is not working

just convert

scanf( "%s", input);

to

scanf( "%c", &input);

that will be enough

Answer 2

the main problem is input stream

for single char input in scanf

we use scanf( "%c", &input);

but for whole non-space array of characters / string we use

scanf( " %s", str);

for string contains whitespace except new line

gets_s( str, sizeof( str ) ) ;

for your case

correct the following code

scanf( "%s", input);

to

scanf( "%c", &input);

Happy Coding

Answer 3

The problem is: you are getting the input with scanf("%s", input);

therefore the condition input == 'a' is the same as "a" == 'a' which never meets

you need to get the input as a char using

scanf("%c", &input);

not

scanf("%s", input);