C Program to Make a Simple Calculator

Last Updated : 16 May, 2025

A simple calculator is a program that can perform addition, subtraction, multiplication, and division of two numbers provided as input. In this article, we will learn to create a simple calculator program in C.

Example

Input: a = 10, b = 5, op = +
Output: 15.00
Explanation: Chosen operation is addition, so 10 + 5 = 15
Input: a = 12, b = 3, op = /
Output: 4.00
Explanation: The chosen operation is division, so 12 / 3 = 4

Using switch Statement

The switch statement in C is a clean and efficient way to write a conditional code which provides an easy way to write a C program for a simple calculator. Four switch cases can be defined for four operations: addition, subtraction, multiplication, and division, based on the input operator. When the user inputs an operator, the switch statement tests the input against these cases. (i.e., +, -, *, /), and the corresponding operation is executed, and the result is returned.

// C Program to make a Simple Calculator using 
// switch-case statements
#include <stdio.h>
#include <float.h>

int main() {
    char op;
    double a, b, res;

    // Read the operator
    printf("Enter an operator (+, -, *, /): ");
    scanf("%c", &op);

    // Read the two numbers
    printf("Enter two operands: ");
    scanf("%lf %lf", &a, &b);
    
    // Define all four operations in the corresponding
    // switch-case
    switch (op) {
    case '+':
        res = a + b;
        break;
    case '-':
        res = a - b;
        break;
    case '*':
         res = a * b;
        break;
    case '/':
        res = a / b;
        break;
    default:
        printf("Error! Incorrect Operator Value\n");
        res = -DBL_MAX;
    }
    if(res!=-DBL_MAX)
      printf("%.2lf", res);
    
    return 0;
}

Input

Enter an operator (+, -, *, /): +
Enter two operands: 10 5

Output

15.00

NOTE: The break statement in each switch case is used to come out of the switch statement when same case is matched and executed. Otherwise, all the cases after the matching case will be executed.

Using if-else Statement

The if-else if ladder is an alternative but more complex way to create a C program for a simple calculator. The idea is to use a series of if-else-if statements to check the vale of the input operator, perform the corresponding operation. and return the result.

// C Program to implement a Simple Calculator 
// using if-else statements
#include <float.h>
#include <stdio.h>

int main() {
    char op;
    double a, b, res;

    // Read the operator
    printf("Enter an operator (+, -, *, /): ");
    scanf("%c", &op);

    // Read the two numbers
    printf("Enter two operands: ");
    scanf("%lf %lf", &a, &b);

    // Perform the operation corresponding to the
    //  given operator
    if (op == '+')
        res = a + b;
    else if (op == '-')
        res = a - b;
    else if (op == '*')
        res = a * b;
    else if (op == '/')
        res = a / b;
    else {
        printf("Error! Operator is not correct.\n");
        res = -DBL_MAX;
    }
  
    if (res != -DBL_MAX)
        printf("Result: %.2lf\n", res);

    return 0;
}

Input

Enter an operator (+, -, *, /): +
Enter two operands: 10 5

Output

4.00

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C Program to Make a Simple Calculator

Using switch Statement

Using if-else Statement

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