Your program should be
#include <stdio.h>
/* Readability is important. So, indent your code */
/* Notice how I corrected your code and also made it more readable */
int main(void){
    int even = 0;
    int odd = 0;
    int x = 0; /* Initialize x */
    /* int num; Unused variable */
    while(x <= 20 || x % 2 == 0) /* Stop when x is greater than 20 or x is odd */
    {
        printf("\nPlease enter a number");
        scanf("%d", &x);
        if (x % 2 == 0)
            even = even + 1; /* +1, not +x. Or `even++;` */
        else
            odd = odd + 1;   /* +1, not +x. Or `odd++;`  */
    }
    printf("Even numbers = %d", even);
    printf("Odd numbers = %d", odd);
    return 0;
}
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solved C Programming with loops for exam