Which of the following cannot be checked in a switch-case statement?

Which of the following cannot be checked in a switch-case statement?

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1) What will be the output of the following C code? (Assuming that we have entered the value 1 in the standard input)

 #include <stdio.h>
 void main()
 {
   char *ch;
   printf("enter a value between 1 to 3:");
   scanf("%s", ch);
   switch (ch)
   {
     case "1": printf("1");
               break;
     case "2": printf("2");
               break;
   }
 }

2) What will be the output of the following C code? (Assuming that we have entered the value 1 in the standard input)

 #include <stdio.h>
 void main()
 {
    int ch;
    printf("enter a value between 1 to 2:");
    scanf("%d", &ch);
    switch (ch, ch + 1)
    {
      case 1: printf("1\n");
              break;
      case 2: printf("2");
              break;
    }
 }

3) What is the output of this C code?

#include <stdio.h>
     const int a = 1,  b = 2;
     int main()
     {
         int x = 1;
         switch (x)
         {
         case a:             printf("yes ");
         case b:             printf("no\n");
             break;
         }
     }

4) Consider the following code snippet:

 marks =80;
 switch (marks)
 {
   case 60: grade = 'C';
 			break;
   case 70: grade = 'B';
 			break;
   case 80: grade = 'A';
 			break;
   default: grade =  'E';
			 }

5) What is the output of this C code(When 1 is entered)?

#include <stdio.h>
     void main()
     {
         int ch;
         printf("enter a value btw 1 to 2:");
         scanf("%d", &ch);
         switch (ch, ch + 1)
         {
         case 1:             printf("1\n");
             break;
         case 2:             printf("2");
             break;
         }
     }