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Why to avoid goto in C

By Dinesh Thakur

C has GOTO statement but one must ensure not to use too much of goto statement in their program because its functionality is limited and it is only recommended as a last resort if structured solutions are much more complicated. First let us see what the goto statement does, its syntax and functionality. The goto is a unconditional branching statement used to transfer control of the program from one statement to another. Syntax of goto statement is: [Read more…] about Why to avoid goto in C

When is a switch statement better than multiple if statements

By Dinesh Thakur

switch statement is generally best to use when you have more than two conditional expressions based on

a single variable of numeric type. For instance, rather than the code

 

if (x == 1)

printf(“x is equal to one.\n”);

else if (x == 2)

printf(“x is equal to two.\n”);

else if (x == 3)

printf(“x is equal to three.\n”);

else

printf(“x is not equal to one, two, or three.\n”);

the following code is easier to read and maintain:

switch (x)

{

case 1: printf(“x is equal to one.\n”);

break;

case 2: printf(“x is equal to two.\n”);

break;

case 3: printf(“x is equal to three.\n”);

break;

default: printf(“x is not equal to one, two, or three.\n”);

break;

}

 

Notice that for this method to work, the conditional expression must be based on a variable of numeric type in order to use the switch statement. Also, the conditional expression must be based on a single variable. For instance, even though the following if statement contains more than two conditions, it is not a candidate for using a switch statement because it is based on string comparisons and not numeric comparisons:

 

char* name = “Lupto”;

if (!stricmp(name, “Isaac”))

printf(“Your name means ‘Laughter’.\n”);

else if (!stricmp(name, “Amy”))

printf(“Your name means ‘Beloved’.\n “);

else if (!stricmp(name, “Lloyd”))

printf(“Your name means ‘Mysterious’.\n “);

else

printf(“I haven’t a clue as to what your name means.\n”)

 

What is the functionality and restrictions of Modulus Operator

By Dinesh Thakur

When a division is performed the remainder of the operation is given by modulus operator. The modulus operator is denoted in c by symbol %. Say for instance we have two integer values x and y and then the operation x % y called as x modulus y gives the result as (x- (x / y) * y).  Say if x=18 and y =5 the x % y gives value as (18- (18 / 5) * 5) which gives (18-15) which results in 3 in other words the remainder of the division operation. [Read more…] about What is the functionality and restrictions of Modulus Operator

Static Variable in C

By Dinesh Thakur

Static variable in C is a special variable that is stored in the data segment unlike the default automatic variable that is stored in stack. A static variable can be initialized by using keyword static before variable name. As the name indicates, the static variables retain their value as long as the program executes.

This is useful if we want to isolate pieces of a program to prevent accidental changes in global variables. You can declare a static variable by using the static storage class access specifier. For example, [Read more…] about Static Variable in C

What is a Variables? Declaration of Variables.

By Dinesh Thakur

A variable is an object whose value may change during execution of a program. It is a memory location used to store a data value. A variable name should be carefully chosen by the programmer so that its use is reflected in a useful way in the entire program. Variable names are case sensitive. Others are constants whose values cannot be changed during the execution of the program. However, their values have to be declared. In a program a variable may be declared as below. [Read more…] about What is a Variables? Declaration of Variables.

How do You Decide Which Integer Type to Use

By Dinesh Thakur

If you might need large values (above 32,767 or below -32,767), use long. Otherwise, if space is very important (i.e. if there are large arrays or many structures), use short. Otherwise, use int. If well-defined overflow characteristics are important and negative values are not, or if you want to steer clear of sign-extension problems when manipulating bits or bytes, use one of the corresponding unsigned types. (Beware when mixing signed and unsigned values in expressions, though.) Although character types (especially unsigned char) can be used as “tiny” integers, doing so is sometimes more trouble than it’s worth, due to unpredictable sign extension and increased code size. [Read more…] about How do You Decide Which Integer Type to Use

Define the term Scope, Visibility And Lifetime of a Variable

By Dinesh Thakur

An object is recognized by the computer by either its identifier or name. The object may be a variable of basic type or a function, a structure, or a union. The macro names and macro variables do not figure in the scope because macros are replaced by the preprocessor token sequences before the semantic phase of program translation. An identifier may also represent different objects in different scopes. [Read more…] about Define the term Scope, Visibility And Lifetime of a Variable

Data Types along with Their Sizes and Ranges

By Dinesh Thakur

Both variables and the constants may have different types of values. In C language, different forms of data are categorized into a few abstract data types. For example, suppose you are asked to keep the record of the number of passengers in a bus. A variable say N, which is used to denote this number, will have value in whole numbers because the number of passengers cannot be a fractional number. Similarly, for number of students in a class, number of apples in a basket, number of pages in a book, or number of houses in a colony, etc., the values must be in whole numbers. Whole numbers form a category called integers. In C language, this type is coded as int, a short form for integer.

Numbers with a decimal point such as 2.4 or 3.14159 form another category or type, which when declared use float or double before their names. A float refers to a decimal floating point number with single precision (7 significant digits after the decimal point), whereas double is used for numbers with double precision (up to 15 digits after decimal point).

If a variable stands for names of students or for names of cities or names of rivers, etc., its values would be strings of characters such as “John”, “Delhi”, or “Ganga”.

An object of a given data type is stored in a section of memory having a discreet size. Objects of different data types require different amounts of memory. Therefore, it is necessary to specify the type of data that a variable will be having so that the compiler allocates appropriate memory size and address for storing its value. Following table shows the size and range of the basic data types.

Sizes and Ranges of Data Types :

   DATA STRUCTURE TYPE

Furthermore, there are other types such as void. The void is in fact devoid of any type mentioned above; void cannot be used with any data. It is mainly used with functions that do not return any data and pointers. Void is also called incomplete type. Two data types, the Boolean type, denoted in C as Bool, and the numeration type (type code enum) have been added in C-99. However, in C++ language, the code for Boolean type is bool. C language also allows user-defined types such as names of structures, and unions.

What is a Storage class

By Dinesh Thakur

A storage class specifies how the variables are used in the program.

Static storage class or variable

A variable is declared to be static by prefixing its normal declaration with the keyword static, as in static int a;

Since the property of a variable may be stated in any order we could also use int static a; Static variables can be declared within a function. These variables retain their values from the previous call. i.e., the value that they had before returning from the function.

Register storage class

Register variables are stored in the register of the microprocessor. The number of variable which can be declared register are limited. This means that the variable has a maximum size equal to the register size. If more variables are declared as register variable, they are treated as auto variables. A program that uses register variables executes faster as compared to similar program without register variable.

Automatic storage class or variables

The scope of an automatic variable is only for the block, or any block within the block, in which it appears. All variables declared within a function are auto by default. A variable can be defined as automatic by placing the keyword auto at the beginning of the variable declaration.

Example: auto int a;

External Storage class or Global variable

External variables are global to the file in which they are defined. External variables are used only when all functions needed a particular variable. It retains the assigned value within the scope. In the following program variable i is an external variable.

Example: extern int a;

Anatomy of C Program

By Dinesh Thakur

We have some compiler preprocessor commands. This includes various #include files. Then comes the main function. Some name can also be given to the main function. Then, we have the variable declarations used in the main code. Then we have sub-functions. [Read more…] about Anatomy of C Program