void (*foo)();
int (*f1)(double);//传入double，返回int
void (*f2)(char*);//传入char*指针，没有返回值
double* (*f3)(int,int);//返回double指针

int *f4();

     2.使用函数指针

int (*fptr1)(int);
int square(int num){
     return num * num;
}

int n = 5;
fptr1 = square;
printf("%d square is %d\n",n, fptr1(n));
//显示 5 square is 25

typedef int (*funcptr)(int);
.....
funcptr fptr2;
fptr2 = square;

      3.传递函数指针

int add(int num1,int num2){
      return num1 + 怒骂；
}

int sub(int num1,int num2){
     return num1 - num2;
}

typedef int (*fptrOperator)(int,int);

int compute(fptrOperator operator, int num1, int num2){
      return operator(num1,num2);
}

//调用
compute(add,5,6);
compute(sub,5,6);

     4.返回函数指针

fptrOperator select(char opcode){
   switch(opcode){
        case '+': return add;
        case '-': return sub;
   }
}

int evaluate(char opcode,int num1,num2){
    fptrOperator operation = select(opcode);
    return operation(num1,num2);
}

//调用
evaluate('+',5,6);
evaluate('-',5,6);

       5.使用函数指针数组

typedef int (*operation)(int,int);
operation operations[128] = {NULL};

void initializeOperationsArray(){
      operations['+'] = add;
      operations['-'] = sub;
}

int evaluateArray(char opcode,int num1,int num2){
     fptrOperation operation;
    operation = operations[opcode];
    return operation(num1,num2);
}
//调用
initilizeOperationArray();
evaluateArray('+',5,6);