C program to make a calculator that can perform simple arithmetic and toggle between int and double variables - c

Question

I am a bit new to c programming. For my project I have been tasked with developing a simple calculator that asks the user to input an option then that option declares what operation is to be performed (i.e. if the user enters 1, this corresponds to selecting the addition option which then allows the user to add two numbers they choose. I have the majority of the code worked out, but the catch is that I need the calculator to toggle between int and double variables. When the user enters 5, the calculator should now work with integers then if the user hits 5 again, the calculator switches back to doubles and vice versa so long as you want to switch back and forth. The calculator automatically works with doubles. So, more specifically, if I wanted to use integer variables, I would enter 5, then lets say I wanted to switch back to doubles, I should enter five and receive the message "Calculator now works with doubles." So here is my code thus far:
#include<stdio.h>
#include<math.h>
#include<stdbool.h>
int main()
{
int integermode, doublemode, m, a, b, sum2, difference2, product2,
quotient2;
double i, j, sum1, difference1, product1, quotient1;
printf("This program implements a calculator.");
while(m !=6) {
printf("Options:\n");
printf("1 - addition\n2 - subtraction\n3 - multiplication\n4 - division\n5 - toggle calculator type\n6 - exit program\n");
printf("Please enter your option: ");
scanf("%d", &m);
if(m > 6) {
printf("Invalid option.\n");
printf("Options:\n");
printf("1 - addition\n2 - subtraction\n3 - multiplication\n4 - division\n5 - toggle calculator type\n6 - exit program\n");
printf("Please enter your option: ");
scanf("%d", &m);
}
switch (m) {
case 1:
if (integermode == true) {
printf("Enter first term: ");
scanf("%d", &a);
printf("Enter second term: ");
scanf("%d", &b);
printf("The sum is: %d\n", a+b);
break;
}
if (integermode == false) {
printf("Enter first term: ");
scanf("%lf", &i);
printf("Enter second term: ");
scanf("%lf", &j);
printf("The sum is: %.15lf\n", i+j);
}
break;
case 2:
if (integermode == true) {
printf("Enter first term: ");
scanf("%d", &a);
printf("Enter second term: ");
scanf("%d", &b);
printf("The difference is: %d\n", a-b);
break;
}
if (integermode == false) {
printf("Enter first term: ");
scanf("%lf", &i);
printf("Enter second term: ");
scanf("%lf", &j);
printf("The difference is: %.15lf\n", i-j);
}
break;
case 3:
if (integermode == true) {
printf("Enter first term: ");
scanf("%d", &a);
printf("Enter second term: ");
scanf("%d", &b);
printf("The product is: %d\n", a*b);
break;
}
if (integermode == false) {
printf("Enter first term: ");
scanf("%lf", &i);
printf("Enter second term: ");
scanf("%lf", &j);
printf("The product is: %.15lf\n", i*j);
}
break;
case 4:
if (integermode == true) {
printf("Enter first term: ");
scanf("%d", &a);
printf("Enter second term: ");
scanf("%d", &b);
if (b != 0) printf("The quotient is: %d\n", a/b);
if (b == 0) printf("Cannot divide by zero!\n");
break;
}
if (integermode == false) {
printf("Enter first term: ");
scanf("%lf", &i);
printf("Enter second term: ");
scanf("%lf", &j);
if(j != 0) printf("The quotient is: %.15lf\n", i/j);
if(j == 0) printf("Cannot divide by zero!\n");
break;
}
case 5:
if (m = 5) {
integermode = true;
printf("Calculator now works with integers.\n");
}
if (m != 5) integermode = false;
}
}
return 0;
}

Answer 1

General improvements
First off, you should notice your main function is massive for what it needs to accomplish, and takes a ton of indent levels (when properly indented). That is mostly because you've got a ton of duplicated functionality. You could easily extract the code that asks for the input numbers into a function and reuse it, changing only the operation performed in each case. Or probably even better, you could ask for the input numbers as a part of the main while loop, and then perform a different operation with them depending on the operation mode you're in.
You're not using <math.h>, so you can leave it out.
Another thing I've noticed is you don't initialize the m variable before using it in the while loop. That could potentially cause a lot of problems, so you should initialize it to some value that isn't a valid mode, like for example 0 or -1.
You're also using two consecutive if statements when if/else could be used.
if (integermode == true) {
.....
}
if (integermode == false) {
.....
}
is the same as
if (integermode == true) {
.....
} else {
.....
}
but harder to read and less efficient, as you're doing two comparisons instead of one.
Implementation of double/integer modes
About the functionality you want to implement, you could very well define an enumeration with the possible modes:
typedef enum _datamode {
INTEGER_MODE,
DOUBLE_MODE
} data_mode;
and then have a variable holding the current mode:
data_mode datamode = INTEGER_MODE /* Initializing this to the default mode */
then use integers or doubles during the calculation and output depending on the current value of the variable. Of course, this could be done in a shorter way with an integer instead of an enum and a typedef, but I find this to be a more verbose way.
For the inputs and the result, you could use the union C type, which reserves memory for the biggest type you specify inside it and lets you store any of them in it. For example:
union io {
int i;
double d;
} a, b, result;
declares three variables that have the io union as type. That way, you can use them as integers or doubles as you like (as long as you don't mix types up and, for example, store an integer and read it as a double)
Full working implementation
The following would be my implementation of the program you have to do. It could be accomplished in a much shorter way (take into account the switches dealing with enums take a fair bit of the total space) but I think this is way more elegant and verbose.
I've respected your print statements and the flow of your application, even though I think they could be better (maybe this is something your assignment imposes on you?)
Please take this as an opportunity to learn and don't just copy-paste the code.
#include <stdio.h>
#include <stdlib.h>
typedef enum _datamode {
INTEGER_MODE,
DOUBLE_MODE
} data_mode;
typedef enum _operationmode {
ADDITION,
SUBSTRACTION,
MULTIPLICATION,
DIVISION,
TOGGLE,
EXIT
} operation_mode;
operation_mode ask_mode () {
int input = -1;
while (1) {
printf("Options:\n");
printf("1 - addition\n2 - subtraction\n3 - multiplication\n4 - division\n5 - toggle calculator type\n6 - exit program\n");
printf("Please enter your option: ");
scanf("%i", &input);
if (input < 1 || input > 6) {
printf("Invalid option.\n");
} else {
switch (input) {
case 1:
return ADDITION;
case 2:
return SUBSTRACTION;
case 3:
return MULTIPLICATION;
case 4:
return DIVISION;
case 5:
return TOGGLE;
case 6:
return EXIT;
default:
exit(EXIT_FAILURE); /* Error must've occurred in order for a different value to be present */
}
}
}
}
union _io {
int i;
double d;
};
void get_inputs_integer (int *a, int *b) {
printf("Enter first term: ");
scanf("%i", a);
printf("Enter second term: ");
scanf("%i", b);
}
void get_inputs_double (double *a, double *b) {
printf("Enter first term: ");
scanf("%lf", a);
printf("Enter second term: ");
scanf("%lf", b);
}
int main (int argc, char **argv) {
union _io operand1, operand2, result;
operation_mode o_mode;
data_mode d_mode = INTEGER_MODE;
printf("This program implements a calculator.");
do {
o_mode = ask_mode();
if (o_mode == TOGGLE) {
if (d_mode == INTEGER_MODE) {
d_mode = DOUBLE_MODE;
printf("Calculator now on double mode\n");
} else {
d_mode = INTEGER_MODE;
printf("Calculator now on integer mode\n");
}
} else if (o_mode != EXIT) {
if (d_mode == INTEGER_MODE) {
get_inputs_integer(&operand1.i, &operand2.i);
switch (o_mode) {
case ADDITION:
result.i = operand1.i + operand2.i;
break;
case SUBSTRACTION:
result.i = operand1.i - operand2.i;
break;
case MULTIPLICATION:
result.i = operand1.i * operand2.i;
break;
case DIVISION:
result.i = operand1.i / operand2.i;
break;
default:
exit(EXIT_FAILURE); /* Error must've occurred in order for a different value to be present */
}
printf("The result is %i\n", result.i);
} else {
get_inputs_double(&operand1.d, &operand2.d);
switch (o_mode) {
case ADDITION:
result.d = operand1.d + operand2.d;
break;
case SUBSTRACTION:
result.d = operand1.d - operand2.d;
break;
case MULTIPLICATION:
result.d = operand1.d * operand2.d;
break;
case DIVISION:
result.d = operand1.d / operand2.d;
break;
default:
exit(EXIT_FAILURE); /* Error must've occurred in order for a different value to be present */
}
printf("The result is %lf\n", result.d);
}
}
} while (o_mode != EXIT);
}