输入“2473”，则下面程序的运行结果是 int main() {int c; while((c=getchar())!='') switch(c-'2') {case 0: case 1:putchar(c+4); case 2:putchar(c+4);break; case 3:putchar(c+4); default :putchar(c+2);break;} printf(""); return 0;}