關係運算符

下表列出了所有C語言支持的關係運算符。假設變量A=10和變量B=20，則：

操作符	描述	示例
==	檢查兩個操作數的值是否相等，如果是的話那麼條件為真。	(A == B) 不為 true
!=	檢查兩個操作數的值是否相等，如果值不相等，則條件變為真。	(A != B) 為 true
>	檢查左邊的操作數的值是否大於右操作數的值，如果是的話那麼條件為真。	(A > B) 不為 true
<	檢查左邊的操作數的值是否小於右操作數的值，如果是的話那麼條件為真。	(A < B) 為 true
>=	檢查左邊的操作數的值是否大於或等於右操作數的值，如果是的話那麼條件為真。	(A >= B) 不為  true
<=	檢查左邊的操作數的值是否小於或等於右操作數的值，如果是的話那麼條件為真。	(A <= B) 為 true

示例

試試下麵的例子就明白了所有的C語言編程提供的關係運算符：

#include <stdio.h>

main()
{
   int a = 21;
   int b = 10;
   int c ;

   if( a == b )
   {
      printf("Line 1 - a is equal to b
" );
   }
   else
   {
      printf("Line 1 - a is not equal to b
" );
   }
   if ( a < b )
   {
      printf("Line 2 - a is less than b
" );
   }
   else
   {
      printf("Line 2 - a is not less than b
" );
   }
   if ( a > b )
   {
      printf("Line 3 - a is greater than b
" );
   }
   else
   {
      printf("Line 3 - a is not greater than b
" );
   }
   /* Lets change value of a and b */
   a = 5;
   b = 20;
   if ( a <= b )
   {
      printf("Line 4 - a is either less than or equal to  b
" );
   }
   if ( b >= a )
   {
      printf("Line 5 - b is either greater than  or equal to b
" );
   }
}

當編譯和執行上麵的程序就產生以下結果：

Line 1 - a is not equal to b
Line 2 - a is not less than b
Line 3 - a is greater than b
Line 4 - a is either less than or equal to  b
Line 5 - b is either greater than  or equal to b