Tuesday, August 16, 2011

String operations (length, compare, copy, concatenate) without including string.h using C

In C, string.h includes various build in functions for string operations. The main operations are
1. Length of the string (strlen)
The syntax of strlen is :
strlen(string);
It calculates the length of the string and returns its length. For example:

#include<string.h>
string = "Mumbai";
printf("Length = %d",strlen(string));

The above code displays 5, because Mumbai consists of 5 characters. Note: it does not count null character.

2. Joining two strings (strcat)

The syntax of strcat is
strcat(string1,string2);
Now it removes the null character from string1 and joins the first character of string2 at that position. Now string1 consists of both string1 and string2 in joined form. Example:

#include<string.h>
char string1[] = "Anti";
char string2[] = "Particle";
strcat(string1,string2);
printf("%s",string1); //display AntiParticle

3. Comparing two strings(strcmp)

The syntax of strcmp is
strcmp(string1,string2);
It returns 0 if string1 is same as string2 and returns 1 if they are not same. Example:

#include<string.h>
char string1 = "Nepal";
char string2 = "Srilanka";
if(strcmp(string1,string2)==0){
printf("They are equal");
}else{
printf("They are not equal"); //this is executed
} 

4. Copying one string to another (strcpy)

The syntax of strcpy is

strcpy(destination_string, source_string);

It copies the content of source_string to destination_string. Example:

#include<string.h>
char source[] = "Hello";
char destination[10]; //uninitialized
strcpy(destination,source);
printf("%s",destination); //prints Hello 
These are some of the functions in string.h for string operation. To use these functions you must include header file <string.h>. But we can make our own functions to perform above task without including string,h. Here is the complete source code that has own functions find_length (like strlen) to find length, join_strings( like strcat) for joining strings, compare_strings(like strcmp) for comparing two strings and copy_string(like strcpy) to copy one string from another. Observer carefully the code, if you are beginner, you will learn a lot of things about string operation.

Source Code


///fundamental string operation, lenth, concatenation, compare and copy strings without string.h
#include<stdio.h>
#include<stdlib.h>
int find_length(char string[]){
int len = 0,i;
for(i = 0; string[i]!='\0'; i++){
len++;
}
return len;
}
void join_strings(char string1[], char string2[]){
int i, len1, len2;
len1 = find_length(string1);
len2 = find_length(string2);
for(i = len1; i < len1+len2; i++){
string1[i] = string2[i-len1];
}
string1[i] = '\0'; //adding null character at the end of input
}
/*returns 0 if thery are same otherwise returns 1*/
int compare_strings(char string1[], char string2[]){
int len1, len2, i, count = 0;
len1 = find_length(string1);
len2 = find_length(string2);
if(len1!=len2)
return 1;
for(i = 0; i < len1; i++){
if(string1[i] == string2[i])
count++;
}
if(count == len1)
return 0;
return 1;
}
void copy_string(char destination[], char source[]){
int len,i;
len = find_length(source);
for(i = 0; i < len; i++){
destination[i] = source[i];
}
destination[i] = '\0';
}
int main(){
char string1[20], string2[20]; //string variables declaration with size 20
int choice;
while(1){
printf("\n1. Find Length \n2. Concatenate \n3. Compare \n4. Copy \n5. Exit\n");
printf("Enter your choice: ");
scanf("%d",&choice);
switch(choice){
case 1:
printf("Enter the string: ");
scanf("%s",string1);
printf("The length of string is %d", find_length(string1));
break;
case 2:
printf("Enter two strings: ");
scanf("%s%s",string1,string2);
join_strings(string1,string2);
printf("The concatenated string is %s", string1);
break;
case 3:
printf("Enter two strings: ");
scanf("%s%s",string1,string2);
if(compare_strings(string1,string2)==0){
printf("They are equal");
}else{
printf("They are not equal");
}
break;
case 4:
printf("Enter a string: ");
scanf("%s",string1);
printf("String1 = %s\n");
printf("After copying string1 to string 2\n");
copy_string(string2,string1);
printf("String2 = %s",string2);
break;
case 5:
exit(0);
}
}
return 0;
}

Output


string

1 comment:

  1. Please can any1 tell me menu driven program for string operations like copy,compare and concat two strings using pointers and functions

    ReplyDelete