在 C++ switch 语句中，每个 case 标签的表达式必须是整数常量表达式。
例如，以下程序编译失败。
将const放在i之前使上述程序工作。
注意：以上事实仅适用于 C++。在 C 中，这两个程序都会产生错误。在 C 中，使用整数文字不会导致错误。
使用 switch case 查找两个数之间的最大数的程序：
/* 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 */
}
return 0;
}#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 */
}
return 0;
}#include<stdio.h>
int main()
{
int n1=10,n2=11;
// n1 > n2 (10 > 11) is false so using
// logical operator '>', n1 > n2 produces 0
// (0 means false, 1 means true) So, case 0
// is executed as 10 > 11 is false. Here we
// have used type cast to convert boolean to int,
// to avoid warning.
switch((int)(n1 > n2))
{
case 0:
printf("%d is the largestn", n2);
break;
default:
printf("%d is the largestn", n1);
}
// n1 < n2 (10 < 11) is true so using logical
// operator '<', n1 < n2 produces 1 (1 means true,
// 0 means false) So, default is executed as we
// don't have case 1 to be executed.
switch((int)(n1 < n2))
{
case 0:
printf("%d is the largestn", n1);
break;
default:
printf("%d is the largestn", n2);
}
return 0;
}
