如何使用C程序在各种函数计算器上删除隐式函数和冲突的错误声明？

Question

我已经在C程序上完成了此函数计算器的工作，但是我遇到了一个问题，这的确使我发疯。我可以遍历代码和所有内容，但是在编译代码时，我不断得到隐式声明函数和冲突错误。如何解决我的代码以摆脱它们？我是C语言的新手，也是一般编程人员。谢谢：）

#include <stdio.h>


int main(){
 int response;

 do{

displayWelcomeMessage();

scanf("%d",&response);
selectOption(response);
 if(response<-1||response>8){
 printf("Please enter a number between 1 and 8\n");
 }

 }while(response!=-1);

 printf("Thanks for using the program!");
return 0;
}

void selectOption(int response){
 int adder(int x,int y);
 int subtract(int x,int y);
 int multiplicate(int x,int y);
 double divisor(int x,int y);
 int modeOperator(int x,int y);
 int factorialOperator(int x);
 double powerOperator(int x,int y);
 int FibonacciOperator(int x);
 int x,y;
switch(response){
case 1 :
 printf("the result is: %d\n",adder(x,y));
 break;

case 2 :
 printf("the result is: %d\n",subtract(x,y));
 break;

case 3 :
 printf("the result is: %d\n",multiplicate(x,y));
 break;

case 4 :
 printf("the result is: %lf\n",divisor(x,y));
 break;

case 5 :
 printf("the result is: %d\n",modeOperator(x,y));
 break;

case 6 :
 printf("Please enter a variable to calculate the factorial:\n");
 scanf("%d",&x);
 printf("the result is: %d\n",factorialOperator(x));
 break;

case 7 :
 printf("Enter base:\n");
 scanf("%d", &x);
 printf("Enter exponent:\n");
 scanf("%d", &y);
 printf("the result is: %lf\n",powerOperator(x,y));
 break;

case 8 :
 printf("enter a value:\n");
 scanf("%d",&x);
 for(int i=1;i<=x;i++){
 printf("%d\n",FibonacciOperator(i));
     }
 break;
}
}

void displayWelcomeMessage(){
printf("welcome to final programming homework!\n");
printf("please enter 1 for the addition operation\n");
printf("please enter 2 for the subtraction operation\n");
printf("please enter 3 for the multiplication operation\n");
printf("please enter 4 for the division operation\n");
printf("please enter 5 for the mode operation\n");
printf("please enter 6 for the factorial operation\n");
printf("please enter 7 for the power operation\n");
printf("please enter 8 for the Fibonacci operation\n");
printf("please enter -1 to exit\n");
}

int adder(int x,int y){
 printf("please enter two variables to be added:\n");
 scanf("%d %d",&x,&y);
 return x+y;
}

int subtract(int x,int y){
 printf("please enter two variables to be subtracted:\n");
 scanf("%d %d",&x,&y);
 return x-y;
}

int multiplicate(int x,int y){
 printf("please add two variables to be multiplied:\n");
 scanf("%d %d",&x,&y);
 return x*y;
}

double divisor(int x,int y){
 printf("please add two variables to be divided:\n");
 scanf("%d %d",&x,&y);
 return (double)x/(double)y;
}

int modeOperator(int x,int y){
 printf("please add two variables to find the reminder:\n");
 scanf("%d %d",&x,&y);
 return x%y;
}

int factorialOperator(int x){
 if (x==1)
 return 1;
 else
 return x*factorialOperator(x-1);
}

double powerOperator(int x,int y){
 if(y == 0)
 return 1;
 else if(y > 0)
 return (double)x * powerOperator(x,y-1);
 else
 return 1 / powerOperator(x,-y);
}

int FibonacciOperator(int x){
 if (x==1 || x==2)
 return 1;
 else
 return FibonacciOperator(x-1)+FibonacciOperator(x-2);
}

Answer 1

您需要在定义之前包括所使用功能的头文件。因为它们来自诸如scanf之类的标准库，或者因为您稍后定义了它们。

Answer 2

您在定义或声明函数之前先调用它们。

C编译器仅运行一次，因此，如果在声明函数之前调用函数，则会收到警告。在这种情况下，编译器将假定函数返回int。然后，当编译器找到实际定义时，如果它与隐式定义不匹配，则会出现错误。

您可以通过重新排列功能，以便在使用前对其进行定义，或者在文件顶部添加这些功能的声明来解决此问题。

所以代替：

int main(){
    ...
    displayWelcomeMessage();
    ...
}

void displayWelcomeMessage(){
    ...
}

您想要：

void displayWelcomeMessage(){
    ...
}

int main(){
    ...
    displayWelcomeMessage();
    ...
}

或：

void displayWelcomeMessage();

int main(){
    ...
    displayWelcomeMessage();
    ...
}

void displayWelcomeMessage(){
    ...
}

对main以外的所有功能都执行相同的操作。