Home » C programs » C Strings User-defined Functions Programs

C program to concatenate two strings without using library function

Problem statement

In this program, we will learn how to concatenate or add two strings without using library function? Here we are implementing a function like strcat() that will add two strings.

Implementing stringCat() in C

The function stringCat() will be used in this program to concatenate two strings, where strings will be read by the user.

Program to concatenate/add two strings without using library function in C

#include <stdio.h>
#include <string.h>
#define MAX_SIZE 100

/********************************************************
    *   function name       :stringCat
    *   Parameter           :char* s1,char* s2
    *   Return              :void
    *   Description         :Concatenate  two strings
********************************************************/
void stringCat(char *s1, char *s2);

int main() {
  char str1[MAX_SIZE], str2[MAX_SIZE];

  printf("Enter  string 1 : ");
  scanf("%[^\n]s", str1);  // read string with spaces

  getchar();  // read enter after entering first string

  printf("Enter  string 2 : ");
  scanf("%[^\n]s", str2);  // read string with spaces

  stringCat(str1, str2);
  printf("\nAfter concatenate strings are :\n");
  printf("String 1: %s \nString 2: %s", str1, str2);

  printf("\n");
  return 0;
}

/******** function definition *******/
void stringCat(char *s1, char *s2) {
  int len, i;
  len = strlen(s1) + strlen(s2);
  if (len > MAX_SIZE) {
    printf("\nCan not Concatenate !!!");
    return;
  }

  len = strlen(s1);
  for (i = 0; i < strlen(s2); i++) {
    s1[len + i] = s2[i];
  }
  s1[len + i] = '\0'; /* terminates by NULL*/
}

Output

Enter  string 1 : Hello
Enter  string 2 : Friends

After concatenate strings are :
String 1: HelloFriends
String 2: Friends

C Strings User-defined Functions Programs »