如何指向和修改全局变量-C编程

我试图在一个名为“userval”的函数中引用全局变量,然后根据用户输入修改这些变量。我是否需要在函数末尾返回这些变量?

我试图通过在main函数中打印这些全局变量来检查代码。然而,我不断得到随机字符。

下面是我的代码。

#include <stdio.h>
#include <string.h>
#include <stdlib.h>
// Global Constants
#define MAX_PSWD_LEN 80
char password = 0;
int len = 0;
int upper = 0;
int lower = 0;
int digit = 0;
int special = 0;

int main(int argc, char *argv[]) {
  userval();
  printf(&len);
  printf(&upper);
  printf(&lower);
  printf(&digit);
  printf(&special);

}

int userval() {

printf("Please enter the minimum length of your password: \n");
scanf("%d", &len);
printf("Please enter the minimum number of uppercase letters in your password: \n");
scanf("%d", &upper);
printf("Please enter the minimum number of lowercase letters in your password: \n");
scanf("%d", &lower);
printf("Please enter the minimum number of decimal digit characters in your password: \n");
scanf("%d", &digit);
printf("Please enter the minimum number of special characters in your password: \n");
scanf("%d", &special);

printf("Thank you. \n");

return len, upper, lower, digit, special;
}