The array s1 outputs "HELLOHELL" and then repeats the string "HELLA"

I think you should add this code value = scanf("%s %d %s\n", name, &num, s2); cause while(value != EOF); And just using strncpy, strncmp, strncat in string.h will not working well. I'll suggest you to implement them.

I have fixed the problem and I am getting the right answer now. However, I am still getting wrong answer.