第六章——Making Decisions 进行判断（书中实例代码分析）

第一题：计算某个整数的绝对值

练习目的：if 语句

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 #include<stdio.h>
int main(void)
{
          int number;  -------------------------------#定义一个整型变量number

           printf(" Type in your number: ");
           scanf(" %i ",&number);  ------------------#接收一个键盘输入的整数并赋值给number

           if (number<0)  ---------------------------#开始判断number（如满足条件执行if后语句，如果不满足，则不执行 if后面的语句）
                number=-number;  -------------------#重新给number赋值

 printf("The absoulte value is %i/n",number);  ---#输出number

 return 0;

}

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第二题：计算一组数的平均值，并统计出小于65分数的个数

学习目的：if 语句 + for 语句

#include<stdio.h>
int main(void)
{
     int numberofGrades,i,grade;
     int gradeTotal=0;
     int failureCount=0;  ---------------------------  #定义五个变量，四个为整理，一个为浮点型 
     float average;

     printf("How many grades will you be entering?");
     scanf(" %i ",&numberofGrades);   --------------#得到键盘输入的一个值来确定有几个数字参与操作

    for (i=1;i<=numberofGrades;++i){  -------#以输入的数字为条件来循环
          printf("Enter great #%i:",i);
          scanf (" %i",&grade);  ---------#开始接收第一个数字（grade)

         gradeTotal =gradeTotal+grade;- ---------#把每次循环接收到的数字(grade)相加并存入gradeTotal

          if (grade<65)  -------------#判断每次来循环的数字是否小于65
             ++failureCount; --------#如果是则将先前定义为0的变量failures加1
     }

 average=(float)gradeTotal/numberofGrades; -------#如果此句去掉（float)会是一个什么结果？

 printf("/nGrade average= %.2f/n",average);
 printf("Number of failures=%i/n", failureCount); ----------#输出结果
 
 return 0;
}

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第三题 判断输入的数字是基数还是偶数(此题不在加注释）

目的：if 语句

#include<stdio.h>
int main(void)
{
     int number_to_test,remainder;

     printf("Enter your number to be tested.:");
     scanf(" %i",&number_to_test);

     remainder=number_to_test%2;

     if (remainder==0)
         printf("The number is even./n");

     if (remainder!=0)
         printf("The number is odd./n");

   return 0;
}