Analysis of Common Errors in C Language Learning

Analysis of Common Errors in C Language Learning

Error category
Syntax Error

Logical error

Running Error
0. Forget to define the variable:
Int main ()
{

X = 3; y = 6;
Printf ("% d/n", x + y );

}

1. C language variables must be defined before they can be used;

2. the type of input and output data is different from the format specifier used
Int a = 3; float B = 4.5; printf ("% f % d/n", a, B );

They are not converted according to the assignment rules (for example, 4.5 is converted to 4 ), instead, the data format in the storage unit is organized and output according to the format characters (for example, B occupies 4 bytes, and only the data of the last two bytes is output by % d as an integer)

3. Do not pay attention to the value range of int type data
The value range of int type data (-32768 ~ 32768)
Int num = 89101;
Printf ("% d", num );
It will take over 16 digits to get 23563.
Note: The long type is defined, and the "% d" operator is still used in the output. The above error will still occur.

4. You forgot to use the address character when entering the variable.
Scanf ("% d", a, B );

5. The organization and requirements for data input are inconsistent
Except the format specifiers, the format strings in the scanf function must be input as is.

6. mistaken "=" as "equal to" comparison character
"=" Is a value-added operator
"=" Is a comparison operator.

7. The semicolon is missing after the statement
{
T =;
A = B;
B = t
}
It is pascal's syntax.

8. Add a semicolon to the place where the number should not be added
If (a> B );
Printf ("a is larger than B/n ");

For (I = 0; I <10; I ++ );
{
Scanf ("% d", & x );
Printf ("% d/n", x * x );
}

9. For the compound statement that should contain curly arc, forget to add the curly arc.
Sum = 0;
I = 1;
While (I <= 100)
Sum = sum + 1;
I ++;
10. The arc is not paired.
While (c = getchar ()! = '#')
Putchar (c );

11. I forgot the differences between uppercase and lowercase letters when using the logo.
{
Int a, B, c;
A = 2;
B = 3;
C = A + B;
Printf ("% d + % d = % D", A, B, C );
}

12. Misuse of Circular Arc When referencing array elements
{
Int I, a (10 );
For (I = 0; I <10; I ++)
Scanf ("% d", & a (I ));
}

13. When defining an array, the defined "number of elements" is mistaken for the "Maximum number of available sub-values"
{
Int a [10] = {1, 2, 4, 5, 6, 7, 8, 9, 10 };
Int I;
For (I = 1; I <= 10; I ++)
Printf ("% d", a [I]);
}

14. The definition and reference methods for two-dimensional or multi-dimensional arrays are incorrect.
{
Int a [5, 4];
...
Printf ("% d", a [1 + 2, 2 + 2]);
...
}

15. The array name indicates all elements in the array.
{Int a [4] = {1, 2, 3, 4 };
Printf ("% d", );
}

16. Differences between character arrays and character pointers
Main ()
{
Char str [40];
Str = "Computer and c ";
Printf ("% s/n", str );
}

17. No definite value is assigned to the pointer variable before it is referenced.
{
Char * p;
Scanf ("% s", p );
}

{
Char * p, c [20];
P = c;
Scanf ("% s", p );
}

18. The break statement is missing from the branches of the switch statement.
Mixed character and string representation
...
Char sex;
Sex = "M ";
...

19. errors caused by the use of the auto-increment (++) and auto-Subtract (--) Operators
{
Int * p, a [5] = {1, 3, 5, 7, 9 };
P =;
Printf ("% d", * p ++ );
}

Note the difference between * (++ p;

20. The called function is defined after the call statement, but not described before the call.
Main ()
{Float x, y, z;
X = 3.5; y =-7.6;
Z = max (x, y );
Printf ("% f", z );
}
Float max (float x, float y)
{
Return (x> y? X: y );
}

21. Mistaken changes to the parameter value will affect the value of the real parameter.
Swap (int x, int y)
{Int t;
T = x; x = y; y = t;
}
Main ()
{Int a, B;
A = 3; B = 4;
Swap (a, B );
Printf ("% d, % d/n", a, B );
}

22. The real parameters and parameter types of the function are inconsistent.
Fun (float x, float y)
Main ()
{
Int a = 3, B = 4;
C = fun (a, B );
...
}

23. Mixed Type pointers of different classes
{
Int I = 3, * p1;
Float a = 1.5, * p2;
P1 = & I; p2 = &;
P2 = p1;
Printf ("% d, % d/n", * p1, * p2 );
}

24. Do not pay attention to the order in which function parameters are evaluated
Int I = 3;
Prinft ("% d, % d, % d/n", I, ++ I, ++ I );
Result 5, 4
Because VC ++ calculates the function value in the order from right to left.
The C standard does not specify the order in which function parameters are evaluated.

25. Differences between obfuscation array names and pointer Variables
{Int I, a [5];
For (I = 0; I <5; I ++)
Scanf ("% d", a ++ );
}

{Int a [5], * p;
P =;
For (int I = 0; I <5; I ++)
Scanf ("% d", p ++)
}
{Int a [5], * p;
For (p = a; p scanf ("% d", p );
}

26. Differences between obfuscation struct types and struct Variables
Struct worker
{Long int num;
Char name [20];
Char sex;
Int age;
};
Worker. num= 187045;
Strcpy (worker. name, "ZhangFun ");
Worker. sex = 'M ';
Worker. age = 18;

27. I forgot to open the file while using it. I opened it in read-only mode, but tried to output data to the file.
If (fp = fopen ("test", "r") = NULL)
{Printf ("cannot open this file/n ");
Exit (0 );
}
Ch = fgetc (fp );
While (ch! = '#')
{Ch = ch + 4;
Fputc (ch, fp );
Ch = fgetc (fp );
}