For our second tutorial, we will look at creating variables, getting user input to fill those variables, the IF/Then statement, math, and printing output.
Below is the code, not including comments:
| #include <cstdio> #include <iostream> using namespace std; int main() { float num1; float num2; int num3; float num4; cout << "Enter a number: " << endl; cin >> num1; cout << "Enter a second number: " << endl; cin >> num2; cout << "Choose an operation." << endl; cout << "Enter 1 to add, 2 to subtract, 3 to multiply, 4 to divide: " << endl; cin >> num3; if (num3 >4 || num3 <1) { cout << "Your operation choice isn't valid! Please run the program again." << endl; cout << "Press Enter to end program." << endl; getchar(); return 0; } else { if (num3 == 1) { num4 = num1 + num2; cout << "Result is: "<< num4 << endl; } else if (num3 == 2) { num4 = num1 - num2; cout << "Result is: "<< num4 << endl; } else if (num3 == 3) { num4 = num1 * num2; cout << "Result is: "<< num4 << endl; } else if (num3 == 4) { num4 = num1 / num2; cout << "Result is: " << num4 << endl; } } cout << "Press Enter to end program." << endl; getchar(); return 0; } |
Below is the code, commented to discuss the new items we are seeing:
| #include <cstdio> #include <iostream> using namespace std; int main() { //These are the variables we will be using //"int" tells the program to expect only integers //"float" tells the program that it may have to use floating point numbers (decimals) //Each line creates a variable we can use later. In C++ you can't use a variable you haven't created. float num1; float num2; int num3; float num4; // "cout" prints a line out to the standard output (in this case the screen) // the output can be changed to a file, etc with methods we will learn in future tutorials cout << "Enter a number: " << endl; // "cin" reads from the screen. It stops when Enter is pressed. //In this case, if the input isn't a number, the program will error out. cin >> num1; cout << "Enter a second number: " << endl; cin >> num2; cout << "Choose an operation." << endl; cout << "Enter 1 to add, 2 to subtract, 3 to multiply, 4 to divide: " << endl; //We use cin here to grab the user's selection as to the operation they want to perform //We are only collecting a number at this point, and will apply logic to the number later to match the user's intentions cin >> num3; //First, lets make sure the number is in our intended range (1-4) //We can use an if statement for this if (num3 >4 || num3 <1) //the above line checks to see if the number is greater than 4 or less than 1 //If it is either of those, the program ends with the below message { cout << "Your operation choice isn't valid! Please run the program again." << endl; cout << "Press Enter to end program." << endl; getchar(); return 0; } //If the number is not greater than 4 or less than 1, we continue below else { //In each case here, we are checking to see which number the user has entered //We can use an if statement for this as well - notice that this if statement is still within the "else" //condition of the prior if statement //Once the if statement is satisfied, we are performing an action //First, we calculate num4 based on the user's selection //Then we print a line out (cout) which prints the text "Result is: " to the screen, then the calculated number if (num3 == 1) { num4 = num1 + num2; cout << "Result is: "<< num4 << endl; } else if (num3 == 2) { num4 = num1 - num2; cout << "Result is: "<< num4 << endl; } else if (num3 == 3) { num4 = num1 * num2; cout << "Result is: "<< num4 << endl; } else if (num3 == 4) { num4 = num1 / num2; cout << "Result is: " << num4 << endl; } } //The below line is here to pause the program and allow the user to ponder the result //Once Enter is hit, the program ends cout << "Press Enter to end program." << endl; getchar(); return 0; } |
Thinking through each line of the code should give you some feel for control structures (If/Then) and some ways of both getting data from the user and printing data back out to the screen.
