下表列出了所有C语言支持的关系运算符。假设变量A=10和变量B=20，则：
| 操作符 | 描述 | 示例 |
|---|---|---|
| == | 检查两个操作数的值是否相等，如果是的话那么条件为真。 | (A == B) 不为 true |
| != | 检查两个操作数的值是否相等，如果值不相等，则条件变为真。 | (A != B) 为 true |
| > | 检查左边的操作数的值是否大于右操作数的值，如果是的话那么条件为真。 | (A > B) 不为 true |
| < | 检查左边的操作数的值是否小于右操作数的值，如果是的话那么条件为真。 | (A < B) 为 true |
| >= | 检查左边的操作数的值是否大于或等于右操作数的值，如果是的话那么条件为真。 | (A >= B) 不为 true |
| <= | 检查左边的操作数的值是否小于或等于右操作数的值，如果是的话那么条件为真。 |
(A <= B) 为 true |
示例
试试下面的例子就明白了所有的C语言编程提供的关系运算符：
#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 " ); } }
当编译和执行上面的程序就产生以下结果：
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
