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