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Error Basics in C++

C++ Taking the Bull by the Horns Part 17

Forward: In this part of the series, we look at basics of errors in C++.

By: Chrysanthus Date Published: 22 Aug 2012


This is part 17 of my series, C++ Taking the Bull by the Horns. In this part of the series, we look at basics of errors in C++.

Note: If you cannot see the code or if you think anything is missing (broken link, image absent), just contact me at That is, contact me for the slightest problem you have about what you are reading.

Programming Errors
There are three types of programming errors. In other words, there are three types of errors that can occur in a program. You have Syntax Errors, Logic Errors and Runtime Errors.

Syntax Errors
This is the wrong use of syntax. These errors are wrong statements. When you type a statement, which is wrong, that is a syntax error. Such a statement cannot be executed. For example, you can mistakenly define an identifier, without a preceding object type (e.g. int). Under this condition, your program will not be compiled, and you will never have an executable form of it. During the attempted compilation, indication of the error or errors will be displayed on the screen. The line number (counting text lines from the top of the source code file) of the syntax error, may also be displayed on the screen.

Logic Errors
In this case, C++ understands your program very well, the program is compiled and it executes the program. However, the program will not do what you wanted it to do. It will do something slightly different or completely different. The fault is yours. For example, a loop that is required to do 10 iterations might do 5 iterations, because you coded it mistakenly to do 5 iterations. Another example is that a loop might iterate infinitely, because the condition you gave for the loop made it that way. Logic Errors occur when the program is being executed. The only way to solve this problem is to test your program very well before you hand it to the customer (who asked for it).

Runtime Errors
Runtime errors occur when the program is being executed as a result of the fact that you did not take certain factor into consideration when coding. For example, let us say your code is to divide 8 by some denominator that the user inputs. If the user inputs 2, the division will work, giving you 4 as answer. If the user inputs zero, the division will not work, because 8/0 is undefined. When a runtime error occurs your program normally crashes (and stops). To solve runtime errors, you have to write extra code that will prevent the execution of the particular code segment from taking place, under certain conditions. In this division example, you have to write code that will prevent division by zero from taking place, and possibly informing the user of the mistake he made by inputting zero as a denominator.

Preventing Runtime Errors
The following code illustrates how to prevent the above error (division by zero).

#include <iostream>
using namespace std;

int main()
        int numerator = 8;
        int denominator = 2;

        if (denominator != 0 )
                int answer = numerator/denominator;
                cout << answer;
                cout << "Division by zero is not allowed!";
        return 0;

The particular code segment here is that of the if-block. Read and try the above code if you have not already done so. The code should be self-explanatory. Change the value of the denominator from 2 to 0 and try the code again.

Let us stop here for this part of the series. We continue in the next part.


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