菜鸟求问：用if单分支选择语句替换switch语句？if...else呢？
主要是关于default情况的处理，代码如下：
/*Fig.4.7:fig04_07.c
Countinglettergrades*/
#include
/*functionmainbeginsprogramexecution*/
intmain(void)
{
intgrade;/*onegrade*/
intaCount=0;/*numberofAs*/
intbCount=0;/*numberofBs*/
intcCount=0;/*numberofCs*/
intdCount=0;/*numberofDs*/
intfCount=0;/*numberofFs*/
printf("Enterthelettergrades.\n");
printf("EntertheEOFcharactertoendinput.\n");
/*loopuntilusertypesend-of-filekeysequence*/
while((grade=getchar())!=EOF){
/*determinewhichgradewasinput*/
switch(grade){/*switchnestedinwhile*/
case'A':/*gradewasuppercaseA*/
case'a':/*orlowercasea*/
++aCount;/*incrementaCount*/
break;/*necessarytoexitswitch*/
case'B':/*gradewasuppercaseB*/
case'b':/*orlowercaseb*/
++bCount;/*incrementbCount*/
break;/*exitswitch*/
case'C':/*gradewasuppercaseC*/
case'c':/*orlowercasec*/
++cCount;/*incrementcCount*/
