What should be data type of case labels of switch statement in C?

In C switch statement, the expression of each case label must be an integer constant expression.

For example, the following program fails in compilation.

/* Using non-const in case label */ #include<stdio.h> int main() {   int i = 10;   int c = 10;   switch(c)   {     case i: // not a "const int" expression          printf("Value of c = %d", c);          break;     /*Some more cases */                        }   getchar();   return 0; }

Putting const before i makes the above program work.

#include<stdio.h> int main() {   const int i = 10;   int c = 10;   switch(c)   {     case i:  // Works fine          printf("Value of c = %d", c);          break;     /*Some more cases */                        }   getchar();   return 0; }