Wednesday, 18 January 2017

Reverse of a string in C programming(c programming examples)(c program examples)

Reverse of a string in C programming

This is an example in C covering the functions of 'string.h'. The above program is to find the reverse of the string which is entered by the user. It is simple when we use 'strrev()' function. But there are two programs which get the same output. Among them, one program is using the loop, and the other one is using the string function.


If you want to see this code with a perfect indentation, copy the code into "sublime text editor" and make sure that the type of code is set to 'c' at the bottom right of the window. After pasting the code press the command "ctrl+shift+P", you get a search box. Type "indentation" you get an option like this below the search box "Indentation: Reindent lines". Clink on that to get the code with indentation. 


There are two methods to revers a string:

1. Without any string function:

#include <stdio.h>
main()
{
char a[1000],rev[1000];
int i,j=0,count=0;
printf("enter any string\n");
gets(a);
for(i=0;a[i]!='\0';i++)
count++;
for(i=count-1;i>=0;i--)
{
rev[j]=a[i];
j++;
}
rev[j]='\0';
printf("the reverse of the given string is '%s'",rev);

return 0;
}


2. With string function:

#include <stdio.h>
#include <string.h>
main()
{
char a[1000];
printf("enter any string\n");
gets(a);
strrev(a);
printf("the reverse of the given string is '%s'\n",a );
return 0;
}

The output is as follows:






#include <stdio.h>


The '#include' is a preprocessor directive which includes the source files inside the code. The 'stdio.h' is a standard input and output header file with several functions written in it. The functions like 'printf()''gets()' and 'scanf()' are work when we include 'stdio.h' header file. 

char a[1000],rev[1000];



The data type 'char' is used to declare the are or arrays which are to be used to carry the character data. We declared two arrays 'a[]' and 'rev[]'. The array 'a[]' is used to store the string given by the user and the array 'rev[]' is used to store the reverse of the string.

int i,j=0,count=0;

The data type 'int' is used to declare the variables which carry the integer date within them. We declared three variables 'i', 'j' and 'count'. The variables 'i' and 'j' are used to browse the elements of the two arrays and the variable 'count' is used to count the number of characters in the given string.

printf("enter any string\n");
gets(a);

The message "enter any string" is printed on the screen with the help of the function 'printf()' ,which is predefined in the 'stdio.h' header file. To assign the given string into the array the function 'gets()' is used and this function is also predefined in the 'stdio.h' header file.

for(i=0;a[i]!='\0';i++)
count++;

This is a small 'for loop' to count the number of characters in the given string. The body of loop executes up to the element before the null character in the string. The end value of 'count' is referred as the size of the string.

for(i=count-1;i>=0;i--)
{
rev[j]=a[i];
j++;
}

This 'for loop' is the main logic of the program. It assigns the characters of the string in a reverse order into the array 'rev[]'. The last character in the array 'a[]' is assigned into the first box of the array 'res[]'. And this goes on up to the starting of the array. After every iteration, the value of 'j' is increased by one to assign a new value to the next box of the array 'rev[]'.


rev[j]='\0'

A null character is placed in the last box of the array 'rev[]' to tell the computer that it is the end of the string. whenever we print the string it prints up to its null character.


Second program:

strrev(a);

This single line replaces all the for loops in the first program. But to know how it is working the first program helps a lot. The function 'strrev()' is a function which is predefined in the 'string.h' header file. Whenever we use a string function in any program we should include the header file 'string.h'.

Hence the problem is solved and another program gets into the bucket.


C is a general-purpose programming language. It has been closely associated with the UNIX system where is was developed, since both the system and most of the programs that run on it are written in C. The language, however, is not tied to any one operating system or machine; and although it has been called a “system programming language” because it is useful for writing compilers and operating systems, it has been used equally well to write major programs in many different domains.(c programming examples)(c program examples)
Many of the important ideas of C stem from the language BCPL, developed by Martin Richards. The influence of BCPL on C proceeded indirectly through the language B, which was written by Ken Thompson in 1970 for the first UNIX system on the DEC PDP-7.(c programming examples)
BCPL and B are “typeless” languages. By contrast, C provides a variety of data types. The fundamental types are characters, and integers and floating point numbers of several sizes. In addition, there is a hierarchy of derived data types created with pointers, arrays, structures, and unions. Expressions are formed from operators and operands; any expression, including an assignment or a function call, can be a statement. Pointers provide for machine-independent address arithmetic.(c programming examples)(c program examples)
C provides the fundamental control-flow constructions required for well-structured programs: statement grouping, decision making (if-else), selecting one of a set of possible cases (switch), looping with the termination test at the top (while, for) or at the bottom (do), and early loop exit (break).(c programming examples)(c program examples)
Functions may return values of basic types, structures, unions, or pointers. Any function may be called recursively. Local variables are typically “automatic,” or created anew with each invocation. Function definitions may not be nested but variables may be declared in a block-structured fashion. The functions of a C program may exist I separate source files that are compiled separately. Variables may be internal to a function, external but know only within a single source file, or visible to the entire program.(c programming examples)(c program examples)
A preprocessing step performs macro substitution on program text, inclusion of other source files, conditional compilation.(c programming examples)(c program examples)
C  is a relatively “low level” language. This characterization is not pejorative; it simply means that C deals with the same sort of object that most computers do, namely characters, numbers, and addresses. These may be combined and moved about with the arithmetic and logical operators implemented by real machines.(c programming examples)(c program examples)
C provides no operations to deal directly with composite objects such as character strings, sets, lists, or arrays. There are no operations that manipulate an entire array or string, although structures may be copied as a unit. The language does not define any storage allocation facility other than static definition and the stack discipline provided by the local variables of functions; there is n heap or garbage collection. Finally, C itself provides no input/output facilities; there are no READ or WRITE statements, and no built-in file access methods. All of these higher-level mechanisms must be provided by explicitly called functions. Most C implementations have included a reasonably standard collection of such functions.(c programming examples)(c program examples)

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