这是什么片code的做，什么也各自使用的符号是什么意思？使用的语言是C，我只是个初学者编码 [英] What does this piece of code do and what does each of the symbols used mean? The language used is C and I am just a beginner to coding

问题描述

跨code，而我不明白这两条线是做来了。拿不拿的语法。请具体说明是什么类型的功能已被使用像如我猜测，出现了第一行使用条件运算符。

 无符号长长base_size = B＆GT; = 2？ （B-2）/ 2：0;
的printf（％LLU \\ n，（base_size *（base_size + 1））/ 2）;
 

解决方案

由于每的运算符优先级是C，第一行是有效的。

 无符号长长base_size =（B＆GT; = 2（B-2）/ 2：0）;
 

现在，在除权pression（）使用的三元操作或有条件的运营商。

由于每 C11 标准，章节6.5.15，语法是

 有条件-EX pression：
                    逻辑或-EX pression
                    逻辑或-EX pression？前pression：有条件-EX pression
 

和语义是[关注我的重点]

  

第一个操作数计算; 之间是有顺序的点
  评价和在第二或第三操作数的评价
  （取计算）。 第二个操作数只有当评估
  首先比较不等于0;第三个操作数只计算，如果
  第一比较等于0;其结果是，第二值
  或第三个操作数（取计算）转换为下面描述的类型^注意。

  
  

^{注意：有条件的前pression不会产生左值}

所以，紧接着，你的情况，

  B＆GT; = 2？ （B-2）/ 2：0
 

第一，第一八佰伴pression， B＆GT; = 2 进行评估。如果 B 的值大于或等于 2 ，它返回 1 ，否则 0 。

• 如果计算结果为 1 ，第二个操作数，（B-2）/ 2 是执行，条件运算符的最终结果是前pression的价值。




• 同样，它的计算结果为 0 ，第三个操作数 0 作为返回的结果有条件的经营者。

最后，三元运算符的返回值被用来初始化无符号长长base_size 变量。

关于第二行，的printf（）是一个标准C库函数，在 stdio.h中原型。你可以找到更多关于这个这里。

Came across a code of which I couldn't understand what these two lines are doing. Can't even get the syntax. Please specify what type of functionalities have been used like for eg I am guessing that there has been a use of conditional operators in the first line.

unsigned long long base_size = b >= 2 ? (b-2)/2:0;
printf("%llu\n",(base_size*(base_size+1))/2);

解决方案

As per the operator priority is c, the first line is effectively

unsigned long long base_size = ( b >= 2 ? (b-2)/2:0 );

Now, the expression inside ( ) uses a ternary operator or Conditional operator.

As per the C11 standard, chapter 6.5.15, the syntax is

conditional-expression:
                    logical-OR-expression
                    logical-OR-expression ? expression : conditional-expression

and the semantics is [follow my emphasis]

The first operand is evaluated; there is a sequence point between its evaluation and the evaluation of the second or third operand (whichever is evaluated). The second operand is evaluated only if the first compares unequal to 0; the third operand is evaluated only if the first compares equal to 0; the result is the value of the second or third operand (whichever is evaluated) converted to the type described below^NOTE.

^{NOTE: A conditional expression does not yield an lvalue.}

So, following that, your case,

b >= 2 ? (b-2)/2:0 

first, the first expression, b >= 2 is evaluated. if b has value greater than or equal to 2, it returns 1, otherwise, 0.

• if it evaluates to 1, the second operand, (b-2)/2 is executed and the final result of the conditional operator is the value of the expression.

• similarly, it evaluates to 0, the third operand 0 is returned as the result of the conditional operator.

Finally, the return value of the ternary operator is used to initialize the unsigned long long base_size variable.

About the second line, printf() is a standard C library function, prototyped in stdio.h. You can find more on this here.

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