simple loop code in C

1. If you enter a character, you implicitly enter another one: the newline, which partially causes the weird behavior. This can be ignored by replacing the format string "%c" with "%c%*c".

2. You check for 'y' twice. Replace the second 'y' with a 'n'.

3. Does not influence the program's action but may improve performance: replace the second if with an else if. This will make the program not even test the condition of the second if clause if the first one evaluates to true.

4. You don't check for another character than y or n. Either add a seperate else or, instead of my point 3., replace the second if by an else¹.

¹ As @JonathanLeffler mentioned in the comments to this answer

When you type in y for userresponse, you probably have to hit Enter after that, right?

Enter counts as a charater! Since it wasn't stored in userresponse, it stays in the input buffer. And the next line to read from the input-buffer is scanf("%c",&x);. So you end up with an Enter in the x variable.

Next, you described that the program displays all the printf messages, even the else ones,"
Do you see the keyword else in your program? (cause I don't)

but at the end it loops like 2 or 4 times, displaying all the printf messages,

There are several ways to avoid that, one will be to add after scanf this:

while((check=getchar()) != EOF && check != '\n');

Any way a minimal code will look like this:

#include <stdio.h>
#include <stdlib.h>

int main(void){
    char a;
    int check,ok=0;

    do {
        printf("Give an A: ");

        if ((scanf("%c",&a)) == 1){
            while((check=getchar()) != EOF && check != '\n');

            if ((a == 'a') || (a == 'A')){
                printf("True\n");
                ok=0;
            } else {
                printf("False\n");
                ok = 1;
            }
        }else{
            printf("Error");
            exit(1);
        }

    }while (ok == 1);

    return 0;
}

But the way how you approach this , a fix will probably look like this:

#include <stdio.h>
#include <stdlib.h>

int main(void){
    char userresponse;
    int check,ok=0;
    char x;

    do {
        printf("are you human:  ");

        if ((scanf("%c",&userresponse)) == 1){
            while((check=getchar()) != EOF && check != '\n');

            if ((userresponse == 'y') || (userresponse == 'Y')){
                printf("welcome\n");
                break;
            } else {
                printf("please leave\n\n");
                printf("type z to repeat");
                if(scanf("%c",&x) == 1){
                    while((check=getchar()) != EOF && check != '\n');
                    if(x=='z' || x == 'Z'){
                        ok = 1;
                    }else{
                        printf("\n");
                        printf("Wrong Input\nGoodBye\n");
                        break;
                    }
                }else{
                    break;
                }
            }
        }else{
            printf("Error");
            exit(1);
        }

    }while (ok == 1);

    return 0;
}

What I'm trying here to explain is that there is no reason to stick with a condition in that while like x=='z', just use another variable like in the above examples.

Just give it a try.

EDIT:

If you need to start form your code, than here is a quick fix:

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    char userresponse;
    char x;

    do {
        printf("are you human");
        if(scanf(" %c", &userresponse) ==1){
            if (userresponse == 'y' || userresponse == 'Y') {
                printf("welcome\n");
            }
            printf("type z to repeat\n");
            if(scanf(" %c", &x) != 1){
                printf("Error");
                exit(1);
            }
        }else{
            printf("Error");
            exit(1);
        }

    } while (x == 'z' || x == 'Z');

    return 0;
}

As you probably see, I try to avoid your problems. 1) I check scanf for errors

2) i put a space in front of %c to avoid '\n'.

3) I check for y and Y and for z and Z.

This works fine:

int main()
{
  char userresponse;
  char x;

  do
  {
    printf("are you human");
    scanf(" %c", &userresponse);

    if (userresponse == 'y')
        printf("welcome\n");
    else
        printf("please leave\n");

    printf("type z to repeat");
    scanf(" %c", &x);
  }
  while (x == 'z');

  return 0;
}