Program should have independent user defined function for each case.

Program:

#include<stdio.h>

#include<conio.h>

void main()

{

    int operator,ans;

    double firstNumber,secondNumber;

    clrscr();

    do

    {

        printf("Enter aoperation:\n1.Addition\n2.Subtraction\n3.Multiplication\n4.Divison");

        scanf("%d", &operator);

        printf("Enter two operands: ");

        scanf("%lf %lf",&firstNumber, &secondNumber);

        switch(operator)

        {

            case 1:

            printf("%.1lf + %.1lf = %.1lf",firstNumber, secondNumber, firstNumber + secondNumber);

            break;

            case 2:

            printf("%.1lf -%.1lf = %.1lf",firstNumber, secondNumber, firstNumber -secondNumber);

            break;

            case …