Simple Calculator in C language

In this tutorial, we are going to see how to build a simple calculator in C language.

We will create a menu driven program where we ask user an option out of available options to perform specific operations.

Demo

Prerequisites

• Enthusiasm and passion to Learn
• Basic knowledge of Ruby language
  • Datatype and Variables
  • Loop
  • Conditional Operators
  • Getting input from User

Solution Steps

Follow the steps below to build the simple calculator in C language.

Setup

Let’s first create the file where we want to write our program. Following is the step for Linux or macOS. You should be able to follow this in Windows easily.

$ mkdir c_programs  # Create a common folder for all C programs
$ cd c_programs     # Enter into the folder
$ code .            # Open the current directory in VS Code

NOTE: In Windows OS, you can open command prompt or powershell and perform commands to achieve similar operations.

Now, under EXPLORER and c_programs menu, click on file icon to create a file and name as calculator.c.

Pseudocode

Pseudocode is a plain language description of the steps for the implementation of any program. It often uses structural conventions of a normal programming language, but is intended for human reading rather than machine reading.

Following is the Pseudocode for our Calculator program:

- print the menu
  - accept the choice from user
    - execute the operation function as per choice
    - exit the program if user enter exit choice
  - print invalid if choice doesn't match any operation
- repeat the menu

Program skeleton

Let’s write the skeleton of our program. Copy following code into calculator.c:

// Calculator in C
#include <stdio.h>

int main() {
  // variable to take choice from user
  int choice;

  // infinite while loop to print the menu till exit is selected
  while(1) {
    // print menu

    // accept choice from user
    scanf("%d", &choice);

    switch(choice) {
      case 1: // operation 1
      case 2: // operation 2
      case 3: // operation 3
      default:
        printf("Invalid Choice Selected!");
    }
  }

  return 0;
}

Print menu in screen

After defining the skeleton, we can now print the menu by writing following code below the print menu line:

printf("\n --- CALCULATOR ---\n");
printf("\n1)Addition");
printf("\n2)Subtraction");
printf("\n3)Multiplication");
printf("\n4)Division");
printf("\n5)Power");
printf("\n6)Exit");

printf("\nEnter Your Choice: ");

NOTE: We can write above in one line as well like following but above is more readable and help fellow programmer to understand your code. So, I would encourage you to write as above.

printf("\n--- CALCULATOR ---\n\n1) Addition\n2) Subtraction\n3) Multiplication\n4) Division\n5) Power\n6) Exit\nEnter Your Choice: ");

Define the exit choice

Since, the exit choice is quite simple, let’s define it first.

We will need to use exit() from the standard library stdlib.h to implement the exit operation.

Update the while statement with exit choice as below:

while(1) {
  // print menu
  printf("\n --- CALCULATOR ---\n");
  printf("\n1)Addition");
  printf("\n2)Subtraction");
  printf("\n3)Multiplication");
  printf("\n4)Division");
  printf("\n5)Power");
  printf("\n6)Exit");

  printf("\n Enter Your Choice: ");
  // accept choice from user
  scanf("%d", &choice);

  switch(choice) {
    case 1: // operation 1
    case 2: // operation 2
    case 3: // operation 3
    case 6:
      printf("\nBye!\n");
      exit(0);
    default:
      printf("Invalid Choice Selected!");
  }
}

Run the program

Now, after above step, you can able to run the program and see how it is going.

Run the following command to compile the C program in Linux or macOS:

$ gcc calculator.c -o calculator

or

$ clang calculator.c -o calculator

After, above step, the compiler will compile the program and create an executable file calculator(defined by -o).

Now, run the executable as:

$ ./calculator
--- CALCULATOR ---

1) Addition
2) Subtraction
3) Multiplication
4) Division
5) Power
6) Exit
Enter Your Choice: 6

Bye!

At present, we have completed one path of our pseudocode i.e

-> print the menu
-> accept the choice from user
-> exit the program if user enter exit choice

Adding switch cases

Now, the main part of program is adding operation function corresponding to each case.

Let’s first update the case with the function names to corresponding operation.

switch(choice) {
  case 1:
    addition();
    break;
  case 2:
    subtraction();
    break;
  case 3:
    multiplication();
    break;
  case 4:
    division();
    break;
  case 5:
    power();
    break;
  case 6:
    printf("\nBye!\n");
    exit(0);
  default:
    printf("Invalid Choice Selected!");
}

Adding operation implementation

Now, we can implement each of above operations. Put following code right below line #include <stdlib.h>:

#include <stdlib.h>

// Calculator Functions
void addition() {
  int num1, num2;

  printf("\nEnter first number: ");
  scanf("%d", &num1);
  printf("\nEnter second number: ");
  scanf("%d", &num2);
  printf("\n[ %d + %d = %d ]\n", num1, num2, (num1 + num2));
}

void subtraction() {
  int num1, num2;

  printf("\nEnter first number: ");
  scanf("%d", &num1);
  printf("\nEnter second number: ");
  scanf("%d", &num2);
  printf("\n[ %d - %d = %d ]\n", num1, num2, (num1 - num2));
}

void multiplication() {
  int num1, num2;

  printf("\nEnter first number: ");
  scanf("%d", &num1);
  printf("\nEnter second number: ");
  scanf("%d", &num2);
  printf("\n[ %d x %d = %d ]\n", num1, num2, (num1 * num2));
}

void division() {
  float num1, num2;

  printf("\nEnter first number: ");
  scanf("%f", &num1);
  printf("\nEnter second number: ");
  scanf("%f", &num2);
  printf("\n[ %.2f / %.2f = %.2f ]\n", num1, num2, (num1 / num2));
}

The last operation is the power function. For this to implement we will use the the pow function provided by standard library math.h.

Add the line #include <math.h> to include math library after #include <stdlib.h>. Then, copy following code for the power function:

void power() {
  float num1, num2;

  printf("\nEnter the number: ");
  scanf("%f", &num1);
  printf("\nEnter the power raised: ");
  scanf("%f", &num2);
  printf("\n[ %.1f^%.2f = %.2f ]\n", num1, num2, pow(num1, num2));
}

NOTE: Notice that the pow function accept double. Hence we have declared num1, num2 as floating type. Also, .2f is to get the floating value up to two decimal places.

Source Code

Find the complete source code of this exercise here.

Important things to remember

• The use of curly braces { ... } here might be different than what you are using or given in book. They may be of the form:

  int main()
  {
    // code
  }
  

  Both are valid. I like to keep the opening brace at the end of statement more like the JavaScript style.

• You can always use different approaches to implement same problem.

Possible optimizations

• You can add other mathematical operations as per your need.
• You can accept multiple operands in operations like addition.
• You can migrate the step of asking numbers from user inside switch statement.