Some details about Multi dimensional arrays in C...

An array can be defined as the collection of variables of the same type that are referenced by a common name. Arrays are of two types namely one dimensional arrays and multi dimensional arrays. One dimensional array consists of finite homogenous elements whereas a multi dimensional array is composed of elements each of which is itself an array. Arrays refer to a named list of a finite number n of similar data elements. Each of the data elements can be referenced respectively by a set of consecutive numbers, usually 0, 1, 2, 3, 4,….., n. the simplest form of a multi dimensional array is the two dimensional array.

You can declare a two dimensional array as follows:
Type array name [ rows ] [ columns ];

Where type is the base data type of the array having name name, rows, the first index, refers to the number of rows in the array and columns, the second index refers to the number of columns in t5he array. For example:

Int sales [ 5 ] [ 10 ] ;

The general form of array initialization is shown below:

Type array name [ size N ] = { value list } ;

The value list is a comma separated list of array elements values. The element’s values in the value list must have the same data type as that of the base type of the array.
Int days [ 5 ] = { 1, 2, 3, 4, 5 } ;

Character arrays can also be initialized as shown below:
Char string [ 10 ] = { ‘c’ , ‘a’ , ‘t’ ‘\0’ } ;

Multi-dimensional arrays can also be initialized in the same way as simple dimensions one. For example:
Int abc [ 3 ] [ 2 ] = { 1, 1,
2, 2,
3, 3 } ;

This can be done it the other way also :
Int abc [ 3 ] [ 2 ] = { 1, 1, 2, 2, 3, 3 } ;

A multi dimensional array of strings can be initialized as shown below:

Type array name [ size N ] = { value list } ;

Here type declares the base type of the array, the array name specifies the name with which the array will be referenced and size defines how many elements the array will hold. The size must be an integer value or integer constant without any sign. The value list is a comma separated list of array’s elements values. The element values in the value list must have the same data type as that of the base type of the array.

Int days [ 5 ] = { 1, 2, 3, 4, 5 } ;

Character arrays can also be initialized as shown below:
Char string [ 10 ] = { ‘c’ , ‘a’ , ‘t’ , ‘s’ , ‘\0’ } ;

Multi dimensional arrays are also initialized in the same as the single dimensional one. For example:
Int cube [ 3 ] [ 2 ] = { 1, 1,
2, 2,
3, 3 } ;
This can be done in the other way also:
Int abc [ 3 ] [ 2 ] = { 1, 1, 2, 2, 3, 3 } ;

A multi dimensional array of strings can be initialized as shown below:
Char abc [ 3 ] [ 2 ] = { “Sunday” , “Monday” } ;

C allows you to skip the size of the array in an array initialization statement. This is called unsized array initialization. C allows arrays of more than 2 dimensions. The exact limit of dimensions is determined by the compiler we are using.

Some details about Strings and Arrays of Strings in C

Multiple character constants can be dealt with in 2 ways in C. if enclosed in single quotes, these are treated as character constants and if enclosed in double quotes, these are treated as string literals. A string literal is a sequence of characters surrounded by double quotes. Each string literal is automatically added with a terminating character ‘\0’. Thus, the string “abc” will actually be represented as follows:

“ abc \0” in the memory and its size is not 3 but 4 characters ( inclusive of terminator character ).

Arrays refer to a named list of a finite number n of similar data structure elements. Each of the data elements can be referenced respectively by a set of consecutive numbers, usually 0, 1, 2, 3, ……., n. if the name of an array of 10 elements is ARR, then its elements will be referred as shown below:

ARR [ 0 ], ARR [ 1 ], ARR [ 2 ], ARR [3], …… ARR [9]

Arrays can be one dimensional, two dimensional or multi dimensional. The functions gets() and puts () are string functions. The gets() function accepts a string of characters entered at the keyboard and places them in the string variable mentioned with it. for example :

Char name[ 21 ];

The above code declares a string namely name which can store 20 valid characters ( width 21 specifies one extra character ‘\0’ with which a string is always terminated ). The function gets() reads a string of maximum 20 characters and stores it in a memory address pointed to by name. As soon as the carriage return is pressed, a null terminator ‘\0’ is automatically placed at the end of the string. The function puts () writes a string on the screen and advances the cursor to the newline. Any subsequent output will appear on the next line of the current output by puts ().

Arrays are a way to group a number of items into a larger unit. Arrays can have data items of simple types like int or float, or even of user defined types like structures and objects. An array can be of strings also. Strings are multi dimensional arrays comprised of elements, each of which is itself an array.

A string is nothing but an array of characters only. In actual C does not have a string data type rather it implements string as single dimension character arrays. Character arrays are terminated by a null character ‘\0’. So, for this reason the character arrays or strings are declared one character larger than the largest string they can hold.

Individual strings of the string array can be accessed easily using the index. The end of a string is determined by checking for null character. The size of the first index ( rows ) determines the number of strings and the size of the second index ( columns ) determines maximum length of each string. By just specifying the first index, an individual string can be accessed. You can declare and handle an array of strings just like a two dimensional array. See an example below:

Char name [10] [20] ;

Here the first dimension declares how many strings will be there in the array and the second dimension declares what will be the maximum length of a string. Unlike C++, C has some different functions for adding or concatenating strings, checking string length and to see the similarity of two strings. The functions are namely strlen, strcmp, strcat, strrev etc and are included in header file string.h. Strings are used for holding long inputs.

Understanding the Structure of a C Program

The best way to get started with any programming language is to study a program, so in order to make you understand C program structure, we will take into consideration an example program whose code is:

1. /* this is a simple c program
2. Written to explain basic program structure */ -------------------------multiple line comment
3. #include //header file. ---------------------- single line comment
4. int main()
5. {
6. return 0;
7. }

This is the simplest C program and this program unfortunately doesn’t do anything. “#include” is called a preprocessor command. It tells the compiler to do processing before the compilation. This command tells the compiler to include the header file “stdio.h” in the program.

Functions are the basic building blocks of any program. The function “main()” is the most important function in any C program. You can say that this is the point of execution of a program. This function should exist as an entry point. Following the main is a pair of parentheses. These two parentheses indicate that the main is a function. Now coming to the opening and closing pair of braces in lines 5 and 7, are used to define the limits of a function or the program. Usually these braces contain executable statements of a function. The main() is preceded by word int. it means that this function returns an integer value. This value is returned using the “return” statement.

Now let’s take a program “abc.C” that does something. It’s same as the previous except that it has an executable statement between the braces in addition to the obligatory return statement. The executable statement calls a function which is already included in the header files as a part of the C library. The function is namely “printf()” and in order to make it print text the desired text is written with quotation marks within the parentheses of the function. The text will be displayed on the monitor when program is run. Notice the semicolon at the end of the executable statements. A semi colon in C is used as a statement terminator.

Consider the following statement:
printf("Hello World!\n");

Notice the “\n” character. The back slash is used to indicate to the compiler that a special character is being inserted. Here “n” indicates a new line. This is used whenever you want to print something in a new line. The function “printf()” prints the text and returns the carriage. Consider the following statements:

int index;

the key word int stands for integer and is used to declare a variable of type integer called index. Always keep in mind that the number of field descriptors and the number of variable definitions must be the same or else the runtime system will generate something we are not expecting. Another common and important part of C program structure is “comments”.Comments are optional but it’s good to include because they make the program more readable although they don’t mean anything to the compiler. Comments are of two types: single line comments and multiple line comments. Single line comments are used to give only one line description of a function or any other statement. A multiple line comment spans through several lines and is used to give a detailed description of a program or function.Look at the above program code for an example of comments. Another important part of a program are statements and expressions which combine variables and constants and can be assignments, function calls etc.Coming to the line breaks they are necessary to for good style formatting of your programs. This makes it easy for you to understand how your program flows when you want to maintain or modify it.You can also use “blank lines” after pre compiler declarations and declaration of new variables.Indentation should also be used in order to make your program more readable and to define the body of functions.

What is Assignment and Logical Comparison in C...

An expression as we all know is composed of one or more operations. When the expression is terminated by a semi colon, it becomes a statement which is the small executable unit in any program. The assignment statements are used to assign a value to a variable. The assigned value can be a constant variable or an expression. An assignment statement can be written in general form as:

A=bcd;

Where A is a variable to whom we are assigning a value and bcd is the assigned value. The “=” sign is called assignment operator. Assignments can be chained together. The assigning operator “=” assigns the value to the left hand operand and returns the value of the assignment. Assignment statements are very much needed for variable initialization since variables are initialized using assignment statements. There are 2 ways to do this:
- Un-initialized variable
- Initialized variable
An un-initialized variable has to be initialized in separate statements whereas an initialized variable combines declaration and assignment in to one statement.

Examples are:
Int a;
a=3; ------------------------uninitialized variable
int a= 3; -------------------- initialized variable

Assignment also follows when you use dynamic initialization. Sometimes variables of different types are mixed with each other. It’s a very common and observed phenomenon. In such cases a type conversion takes place. Here also it follows from the principal of assignment statement that “the value of the right side of the expression or of the assignment is converted to the type of the variable on left side i.e., target variable. Both the sides of assignment should be compatible with each other for type conversion. When conversion takes place from smaller data type to a larger data type no data is lost. Precedence of operators while assigning values with an expression should always be kept in mind.
Some programs need the power of decision making or comparison. This is granted through logical expressions which are nothing but the statements resulting into a 0 (true) or 1 (false) value. These are a combination of constants, variables and logical and relational operators. Be careful that two or more variables and operators should not occur in continuation. A logical expression may contain just one signed or unsigned variable or a constant or it may have two or more also joined by varied relational and logical operators. Following are some valid logical operators: the logical OR operator (||), the logical AND operator (&&) and the logical NOT (!) operator. The OR operator combines 2 expressions as its operands. If either of its operand evaluates to true, the OR operator also evaluates to true. This operator is basically used for testing evaluating expressions. The AND operator combines 2 expressions into one and the operator evaluates to one if and only if both the operands evaluate to 1. The NOT operator works on a single operand since it is a unary operator. It is used to negate or reverse the truth value of the operand. It has a higher precedence than of the relational and logical operators. Therefore, this should be enclosed within parentheses. This operator is useful as a test for zero. OR and AND operators have lower precedence than relational operators. Relational operators are used to define relationships between variables. C provides 6 basic relational operators : < (less than), > (greater than), <= (less than or equal to), >= (greater than or equal to), == (equal to), and != (not equal to). Do not confuse the = and the == operators. “=” is assignment operator whereas “==” is relational equality operator.