* Condition expression

本節介紹條件敍述函式與指令:

　

4if statement : 最常用的條件敍述 ,主要用途--判別, 條件控制.

用法一:

     if( 判斷敍述 ) { 判斷敍述 為真,則執行括號內的敍述.}

    EX:

          if ( x >= 7 ) {

                                printf ( " Learning C program ! \n");

                                i++;

                             }

5上例說明: 當 x>=7時, 則印出"Learning C program !",並將 i 的值加1.

　

          if ( x >= 7 && x<=10 )

                    {

                      if ( y <= -2 || y>=1 )

                            {

                                printf ( "[ 7<=X<=10 ] and [ y<=-2 or y>=1 ]\n");

                                j++;

                            }

                                printf ( "(7<=X<=10)\n");

                                i++;

                     }

5上例說明:1. 使用2個 if 敍述時,要注意結束符號的位置.

                              2. 當 x>=7 且 x<=10時, 則印出"(7<=X<=10)",並將 i 的值加1.

                              3. 當 x ε [7,10]且 y ε (-∞,-2] or [1,∞)時, 

則印出"[ 7<=X<=10 ] and [ y<=-2 or y>=1 ]" ,並將 j 的值加1.

用法二:

     if( 判斷敍述 ) { 判斷敍述 為真,則執行括號內的敍述.}

     else                  { if判斷敍述 不為真,則執行此括號內的敍述.}

    EX:

     if ( seed >= 11)

                     {

AUnifNumber = (double)(rand()%seed)/seed;

                        printf ( "A uniform random number is %.5lf\n", AUnifNumber);                       

                     }

           else

                   {

                       printf ("Input a seed no more than 11\n");

                    }   

5上例說明: 大家應該看得懂吧!