函数中的指针 "expected expression before = token"

Question

我尝试通过 "simply" 数一个圆来学习在函数中使用指针。我收到错误 expected expression before '=' token 但不明白为什么。之前说预期的表达..我不清楚，什么样的？

#define PI = 3.1415f

void circle(float *wert) {

    *wert = ( (*wert) * (*wert) * PI );

}

int main(void) {

    float radius;

    printf("radius input: ");
    scanf("%f", &radius);    
    circle(&radius);
    printf("the circle size will be: %f", &radius);

}

Answer 1

#define PI = 3.1415f

这里应该没有=。换成

#define PI (3.1415f)

Answer 2

#define PI = 3.1415f

应该是

#define PI 3.1415f

宏PI在代码中使用时被替换为3.1415

函数中的指针 "expected expression before = token"

Pointer in a function "expected expression before = token"

c

pointers

c-preprocessor