C Program to Concatenate Two Strings

#include <stdio.h>
#define MAX_SIZE 100 // Maximum string size
int main()
{
    char str1[MAX_SIZE], str2[MAX_SIZE];
    int i, j;
    /* Input two strings from user */
    printf("Enter first string: ");
    gets(str1);
    printf("Enter second string: ");
    gets(str2);
    /* Move till the end of str1 */
    i=0;
    while(str1[i] != '')
    {
        i++;
    }
    /* Copy str2 to str1 */
    j = 0;
    while(str2[j] != '')
    {
        str1[i] = str2[j];
        i++;
        j++;
    }
    // Make sure that str1 is NULL terminated
    str1[i] = '';
    printf("Concatenated string = %s", str1);
    return 0;
}