C program to Concatenate Two Strings

In this article, We will show you, How to write a C program to Concatenate Two Strings without using strcat function. We can concatenate two string in multiple way, but we will discuss four different approaches: using For Loop, While Loop, Functions, and Pointers.

C program to Concatenate Two Strings without using strlcat()

This program allows the user to enter two string values or two character array. Next, it will use For Loop to iterate each and every character present in that arrays, and joins them (or concatenate them)

/* C program to Concatenate Two Strings without using strcat() */

#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str1[100], Str2[100];
  	int i, j;
 
  	printf("\n Please Enter the First String :  ");
  	gets(Str1);
  	
  	printf("\n Please Enter the Second String :  ");
  	gets(Str2);

        // To iterate First String from Start to end  
  	for (i = 0; Str1[i]!='\0'; i++);

        // Concatenating Str2 into Str1  	
  	for (j = 0; Str2[j]!='\0'; j++, i++)
  	{
  		Str1[i] = Str2[j];
  	}
  	Str1[i] = '\0';

  	printf("\n String after the Concatenate = %s", Str1);
  	
  	return 0;
}

OUTPUT

C program to Concatenate Two Strings Using While Loop

This program is same as above but this time we are using While loop (Just replacing For Loop with While Loop). I suggest you to refer While Loop to understand the loop Iteration.

/* C code to Concatenate Two Strings without using strcat() */

#include <stdio.h>
#include <string.h>
 
int main()
{
  	char Str1[100], Str2[100];
  	int i, j;
 
  	printf("\n Please Enter the First String :  ");
  	gets(Str1);
  	
  	printf("\n Please Enter the Second String :  ");
  	gets(Str2);
 
  	i = 0;
	while( Str1[i]!='\0')
	{
		i++;
	}
	
  	j = 0;
  	while( Str2[j]!='\0')
  	{
  		Str1[i] = Str2[j];
  		i++;
  		j++;
  	}
  	Str1[i] = '\0';

  	printf("\n String after the Concatenate = %s", Str1);
  	
  	return 0;
}

OUTPUT

C program to Concatenate Two Strings Using Functions

This program is same as above but this time we are using Functions concept to separate the logic from main program.

/* C program to Concatenate Two Strings without using strcat() */

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

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

int main()
{
  	char Str1[100], Str2[100];
 
  	printf("\n Please Enter the First String :  ");
  	gets(Str1);
  	
  	printf("\n Please Enter the Second String :  ");
  	gets(Str2);
  	
  	concatenate(Str1, Str2);

  	printf("\n String after the Concatenate = %s", Str1);
  	
  	return 0;
}

void concatenate(char s1[], char s2[])
{
	int i, j;
	
	i = 0;
	while( s1[i]!='\0')
	{
		i++;
	}
	
  	j = 0;
  	while( s2[j]!='\0')
  	{
  		s1[i] = s2[j];
  		i++;
  		j++;
  	}
  	s1[i] = '\0';
}

OUTPUT

C program to Concatenate Two Strings Using Pointers

This program is same as second example, but this time we are using Pointers concept.

/* C code to Concatenate Two Strings without using strcat() */

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

int main()
{
  	char Str1[100], Str2[100];
  	char *s1 = Str1;
	char *s2 = Str2;
 
  	printf("\n Please Enter the First String :  ");
  	gets(Str1);
  	
  	printf("\n Please Enter the Second String :  ");
  	gets(Str2);
  	
  	while(* ++s1);
  	
  	while(*(s1++) = (*s2++)); 
  	
  	printf("\n String after the Concatenate = %s", Str1);
  	
  	return 0;
}

OUTPUT

C program to Concatenate Two Strings Using Pointer Functions

This program is same as above but this time we are passing pointers to Functions to separate the logic from main program.

/* C Code to Concate Two Strings without using strcat() */

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

void concatenate(char *, char *); 

int main()
{
  	char Str1[100], Str2[100];
 
  	printf("\n Please Enter the First String :  ");
  	gets(Str1);
  	
  	printf("\n Please Enter the Second String :  ");
  	gets(Str2);
  	
  	concatenate(Str1, Str2);

  	printf("\n String after the Concatenate = %s", Str1);
  	
  	return 0;
}

void concatenate(char *Str1, char *Str2)
{
	while(*Str1)
	{
		Str1++;
	}
	
	while(*Str2)
	{
		*Str1 = *Str2;
		*Str1++;
		*Str2++;
  	}
  	*Str1 = '\0';
}

OUTPUT

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