将代码封装函数，放置单独文件，连接文件运行

Question

哪位码农可以帮我解决，我需要详细步骤才看得懂，（1）将下列加减乘除运算运算封装成一个函数，（2）和将加减运算运算的函数放置的单独文件中，并定义连接文件运行。下面是代码（麻烦各路码农了）if那行 choice我去掉了，不然发不出去，你们加一下：

#include<stdio.h>

int main()

float a,b

flot result；

int choice；

while(1)
{
printf("pla imput choice:\n");
printf("1.add,2.sub,3.mul,4.div,S-exit\n");
scanf("%d",&choice);
if (choice !=1&& !=2&& !=3&& !=4&& !=5)
{
printf("you choice error!\n");
return 0;
}
if(choice==5)
{
return 0;
}
printf("pls intput two flost numer:\n");
scanf("%f %f",&a,&b);
switch(choice)
{
case 1:result=a+b;break;
case 2:result=a-b;break;
case 3:result=a*b;break;
case 4:result=a/b;break;
}
printf("result:%f",result);
}

Answer 1

calc.h

#ifndef CALC_H
#define CALC_H

extern float add(float a, float b);
extern float sub(float a, float b);
extern float mul(float a, float b);
extern float div(float a, float b);

#endif

calc.c

#include "calc.h"

float add(float a, float b) { return a + b; }

float sub(float a, float b) { return a - b; }

float mul(float a, float b) { return a * b; }

float div(float a, float b) { return a / b; }

main.c

#include "calc.h"
#include <stdio.h>

int main() {
  float a, b, r;
  int choice;
  while (1) {
    printf("1: add, 2: sub, 3: mul, 4: div, 5: exit\n");
    printf("Please input choice: ");
    if (scanf("%d", &choice) != 1) {
      printf("input error\n");
      break;
    }
    if (choice < 1 || choice > 5) {
      printf("invalid choice, please try again\n");
      continue;
    }
    if (choice == 5)
      break;
    printf("Please input two float numbers: ");
    if (scanf("%f%f", &a, &b) != 2) {
      printf("input error\n");
      break;
    }
    switch (choice) {
    case 1:
      r = add(a, b);
      break;
    case 2:
      r = sub(a, b);
      break;
    case 3:
      r = mul(a, b);
      break;
    case 4:
      r = div(a, b);
      break;
    default:
      break;
    }
    printf("result: %f\n", r);
  }

  return 0;
}

$ gcc -c calc.c -o calc.o
$ gcc -c main.c -o main.o
$ gcc main.o calc.o -o calc
$ ./calc
1: add, 2: sub, 3: mul, 4: div, 5: exit
Please input choice: 1
Please input two float numbers: 2 3
result: 5.000000
1: add, 2: sub, 3: mul, 4: div, 5: exit
Please input choice: 3
Please input two float numbers: 4 5
result: 20.000000
1: add, 2: sub, 3: mul, 4: div, 5: exit
Please input choice: 5