Error is an illegal operation performed by the user which results in abnormal working of the program.
Programming errors often remain undetected until the program is compiled or executed. Some of the errors inhibit the program from getting compiled or executed. Thus errors should be removed before compiling and executing.
The most common errors can be broadly classified as follows.
Type of errors:
- Syntax errors: Errors that occur when you violate the rules of writing C/C++ syntax are known as syntax errors. This compiler error indicates something that must be fixed before the code can be compiled. All these errors are detected by compiler and thus are known as compile-time errors.
Most frequent syntax errors are:
- Missing Parenthesis (})
- Printing the value of variable without declaring it
- Missing semicolon like this:
C++
#include <iostream>
using namespace std;
void main()
{
int x = 10;
int y = 15;
cout << " "<< (x, y)
}
|
C
#include<stdio.h>
void main()
{
int x = 10;
int y = 15;
printf("%d", (x, y))
}
|
Error:
error: expected ';' before '}' token
- Syntax of a basic construct is written wrong. For example : while loop
C++
#include <iostream>
using namespace std;
int main(void)
{
while(.)
{
cout <<"hello";
}
return 0;
}
|
C
#include<stdio.h>
int main(void)
{
while(.)
{
printf("hello");
}
return 0;
}
|
Error:
error: expected expression before '.' token
while(.)
- In the given example, the syntax of while loop is incorrect. This causes a syntax error.
- Run-time Errors : Errors which occur during program execution(run-time) after successful compilation are called run-time errors. One of the most common run-time error is division by zero also known as Division error. These types of error are hard to find as the compiler doesn’t point to the line at which the error occurs.
For more understanding run the example given below.
C++
#include <iostream>
#include <bits/stdc++.h>
using namespace std;
void main()
{
int n = 9, div = 0;
div = n/0;
cout << "result = "<< div;
}
|
C
#include<stdio.h>
void main()
{
int n = 9, div = 0;
div = n/0;
printf("result = %d", div);
}
|
Error:
warning: division by zero [-Wdiv-by-zero]
div = n/0;
- In the given example, there is Division by zero error. This is an example of run-time error i.e errors occurring while running the program.
- Linker Errors: These error occurs when after compilation we link the different object files with main’s object using Ctrl+F9 key(RUN). These are errors generated when the executable of the program cannot be generated. This may be due to wrong function prototyping, incorrect header files. One of the most common linker error is writing Main() instead of main().
C++
#include <bits/stdc++.h>
using namespace std;
void Main()
{
int a = 10;
cout << " "<< a;
}
|
C
#include<stdio.h>
void Main()
{
int a = 10;
printf("%d", a);
}
|
Error:
(.text+0x20): undefined reference to `main'
- Logical Errors : On compilation and execution of a program, desired output is not obtained when certain input values are given. These types of errors which provide incorrect output but appears to be error free are called logical errors. These are one of the most common errors done by beginners of programming.
These errors solely depend on the logical thinking of the programmer and are easy to detect if we follow the line of execution and determine why the program takes that path of execution.
C++
int main()
{
int i = 0;
for(i = 0; i < 3; i++);
{
cout << "loop ";
continue;
}
return 0;
}
|
C
int main()
{
int i = 0;
for(i = 0; i < 3; i++);
{
printf("loop ");
continue;
}
getchar();
return 0;
}
|
- No output
- Semantic errors : This error occurs when the statements written in the program are not meaningful to the compiler.
C++
int main()
{
int a, b, c;
a + b = c;
}
|
C
void main()
{
int a, b, c;
a + b = c;
}
|
Error:
error: lvalue required as left operand of assignment
a + b = c; //semantic error
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