#include <stdio.h> 
  int main() {
      int x;
      
      printf("输入一个整数: \n");
      scanf("%d",&x);
      
      if(x%2==1)  
          printf("是奇数");
      else
          printf("是偶数"); 
      
      return 0;
  } 

 #include <stdio.h> 
  int main() {
      int days;

      printf("输入一个整数: \n");
      scanf("%d",&days);
      
      if (days==1||days==2||days==3||days==4||days==5)
          printf("workdays, fighting\n");
      else if(days==6||days==7) 
          printf("weekend, relax~\n");
      else
          printf("Ooops, not in 1~7\n");
      
      return 0;
  } 

 #include <stdio.h>
  int main() {
      char ch;
      
      printf("输入一个字符:\n");
      scanf("%c",&ch);
      
      
      if('a'<=ch&&ch<='z')   
          ch=ch-32;     
      else if('A'<=ch&&ch<='Z')
        ch=ch;         
      
      printf("%c\n",ch);
      
      return 0;
  }

体验感想：操作不熟练，规则不清晰，全程翻课本，百度。