Example: C program to make a simple calculator using functions

// C program to make a simple calculator using functions
#include <stdio.h>
#include <limits.h>

// Addition operation
double addition(double operand1, double operand2)
{
    return operand1 + operand2;
}

// Subtraction operation
double subtraction(double operand1, double operand2)
{
    return operand1 - operand2;
}

// Multiplication operation
double multiplication(double operand1, double operand2)
{
    return operand1 * operand2;
}

// Division  operation
double division(double operand1, double operand2)
{
    // Check for division by zero
    if (operand2 != 0)
    {
        return operand1 / operand2;
    }
    else
    {
        printf("\nError! Division by zero.\n");
        return INT_MIN;
    }
}

int main()
{
    char operator;
    double operand1 = 0, operand2 = 0;
    double result = 0;

    // INPUT the operator
    printf("Enter an operator from these - (+, -, *, /): ");
    scanf("%c", &operator);

    // INPUT the two values
    printf("\nEnter the two values to make calculation\n");
    scanf("%lf %lf", &operand1, &operand2);

    if (operator== '+')
    {
        result = addition(operand1, operand2);
    }
    else if (operator== '-')
    {
        result = subtraction(operand1, operand2);
    }
    else if (operator== '*')
    {
        result = multiplication(operand1, operand2);
    }
    else if (operator== '/')
    {
        result = division(operand1, operand2);
    }
    else
    {
        printf("\nError! Operator is not correct.\n");
        result = INT_MIN;
    }

    printf("\nResult: %.2lf\n", result);
    return 0;
}