Program : C Program to Concat Two Strings without Using Library Function

#include<stdio.h>
#include<string.h>

void concat(char[],char[]);

void main()
{
char s1[50],s2[30];
printf("nEnter String 1 :");
gets(s1);
printf("nEnter String 2 :");
gets(s2);

concat(s1,s2);
printf("nConcated string is :%s",s1);
return(0);
}

void concat(char s1[],char s2[])
{
int i,j;

i = strlen(s1);

for(j=0; s2[j] != ''; i++,j++)
      s1[i]=s2[j];

s1[i]='';
}

---

Output of Program :

Enter String 1 : Pritesh
Enter String 2 : Taral
Concated string is : PriteshTaral

Explanation of Code :

Our program starts from main and we are accepting two strings from user using these following statements -

printf("nEnter String 1 :");
gets(s1);
printf("nEnter String 2 :");
gets(s2);

Inside the concate() function we are firstly calculating the size of first string.

i = strlen(s1);

Now we are iterating 2nd string character by character and putting each character to the end of the 1st string.

Explanation of Program With Dry Run :

Step 1 : Input

s1 = "Pritesh"
s2 = "Taral"

Step 2 : Size of Strings

i = strlen(s1);
  = strlen("Pritesh");
  = 7

Step 3 : Concatenating Strings

Last position of s1 = 7

First Character of the 2nd String will be stored at last Position of String 1. thus using for loop -

s1[7]  = "T"
s1[8]  = "a"
s1[9]  = "r"
s1[10] = "a"
s1[11] = "l"