C program to compare, concatenate and append strings using user defined functions

In this article we will learn to implement a C program to compare, concatenate and append strings. A C program is provided below to read two strings and perform comparison, concatenation and append operations.

Program is as follows:

/*
 * C program to implement the following string functions using user defined functions:
 * i. To concatenate two strings
 * ii. To append a string to another string
 * iii. To compare two strings
 * Author: P.S.SuryaTeja
*/
#include <stdio.h>
#include <conio.h>
#include <math.h>
#include <stdlib.h>
#include <string.h>

void concat(char *str1, char *str2)
{
	char str[40];
	int str1length, str2length;
	int i;
	str1length = strlen(str1);
	str2length = strlen(str2);
	for(i = 0; i < str1length; i++)
	{
		str[i] = *str1;
		str1++;
	}
	while(i < str1length + str2length)
	{
		str[i] = *str2;
		str2++;
		i++;
	}
	str[i] = '\0';
	printf("\nResult of concatenation is: ");
	puts(str);
}

void append(char *str1, char *str2)
{
	int str1length, str2length;
	int i;
	char *tempstr;
	tempstr = str1;
	str1length = strlen(str1);
	str2length = strlen(str2);
	for(i = 0; i < str1length; i++)
		str1++;
	for(i = 0; i < str2length; i++)
	{
		*str1 = *str2;
		str1++;
		str2++;
	}
	*str1 = '\0';
	printf("\nResult of appending is: ");
	puts(tempstr);
}

void compare(char *str1, char *str2)
{
	int str1length, str2length;
	int i, flag = 0;
	str1length = strlen(str1);
	str2length = strlen(str2);
	if(str1length != str2length)
		printf("\nBoth strings are not equal");
	else
	{
		for(i = 0; i < str1length; i++)
		{
			if(*str1 != *str2)
				flag = 1;
			str1++;
			str2++;
		}
		if(flag == 0)
			printf("\nBoth strings are equal");
		else
		{
			printf("\nBoth strings are not equal");
		}
	}
}

int main(int argc, char **argv)
{
	char str1[20], str2[20], str3[20];
	printf("Enter string 1: ");
	gets(str1);
	printf("Enter string 2: ");
	gets(str2);
	strcpy(str3,str1);
	printf("\n");
	concat(str1, str2);
	printf("\n");
	append(str1, str2);
	printf("\n");
	compare(str3, str2);
    getch();
    return 0;
}

Input and output for the above program is as follows:

Enter string 1: hai
Enter string 2: hai


Result of concatenation is: haihai


Result of appending is: haihai


Both strings are equal

Suryateja Pericherla

Suryateja Pericherla, at present is a Research Scholar (full-time Ph.D.) in the Dept. of Computer Science & Systems Engineering at Andhra University, Visakhapatnam. Previously worked as an Associate Professor in the Dept. of CSE at Vishnu Institute of Technology, India.

He has 11+ years of teaching experience and is an individual researcher whose research interests are Cloud Computing, Internet of Things, Computer Security, Network Security and Blockchain.

He is a member of professional societies like IEEE, ACM, CSI and ISCA. He published several research papers which are indexed by SCIE, WoS, Scopus, Springer and others.