错误:初始化元素不是常量(c语言)

This is a .h file to store formulas but it gives me the ERROR you see at the tittle on line #16(below the string). I'm a beginner and the error says is not constant so I though of putting "const" before the "float" but it doesn't work either way.

这是一个用于存储公式的.h文件，但是它给出了您在第16行(在字符串下面)看到的错误。我是初学者，错误说的不是常量，所以我把“const”放在“float”之前，但不管用哪种方式都不行。

#ifndef FORMULAS_H_INCLUDED
#define FORMULAS_H_INCLUDED

float a;
float Pi=3.1415926536;
float r;
float b;
float c;
float h;




char formula_volume_cube[100] = "Formula for the Volume of a Cube: V=a*a*a";
const float volume_cube=(a*a*a);



#endif // FORMULAS_H_INCLUDED

Any help will be appreciated. THANK you for YOUR time.

如有任何帮助，我们将不胜感激。谢谢你抽出时间来。

2 个解决方案

#1

Global variables in C can only be initialized with compile-time constant expressions, and that is a very narrow class of expressions. It essentially only comprises literals or expressions involving literals:

C中的全局变量只能用编译时常量表达式初始化，这是一个非常狭窄的表达式类。它实际上只包含了包含文字的文字或表达式:

float a1 = 1.5;                   // OK
const float a2 = 2.5 * 10 / 300;  // Also OK

An expression that identifies another global variable is not a compile-time constant expression:

标识另一个全局变量的表达式不是编译时常量表达式:

// float a3 = a2;                 // Error!

C is just not expressive enough for this. This is all for the sake of simplicity. For example, C does not distinguish between const float b1 = 2.5; and extern const float b2;. The variable b1 is no "more const" than b2, but only b1's value is known to the compiler, whereas b2's value is not known — it may be set only by a different translation unit, and without any ordering. So there's no way to make one constant "more constant" than the other. The simple solution in C is that no id-expression can be used as a compile-time constant.

C只是不够表达。这都是为了简单起见。例如，C不区分const float b1 = 2.5;和外部的const float b2;。变量b1并不比b2更“const”，但是编译器只知道b1的值，而b2的值是未知的——它只能由一个不同的翻译单元来设置，并且没有任何排序。所以没有办法让一个常数比另一个常数“更稳定”。在C中简单的解是没有任何的id表达式可以作为编译时常量。

(C++, by contrast, allows global variables to have dynamic initializers. This introduces a whole set of ordering concerns if one global variable's initializer depends on another global variable. C has none of those problems.)

相比之下，c++允许全局变量具有动态初始化器。如果一个全局变量的初始化器依赖于另一个全局变量，那么就会引发一系列的排序问题。C没有这些问题。

#2

The message

的消息

Error: Initializer Element is not constant

错误:初始化元素不是常量。

pretty much says it all

说得差不多了。

float a;

is not declared as a constant (it can change as the program runs), so

没有被声明为常量(它可以随着程序的运行而改变)，那么?

const float volume_cube=(a*a*a);

cannot be a constant, as it is based on the non-constant a.

不可能是常数，因为它是基于非常数a的。

#1