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

int STRLEN(char s[])
{
	int count = 0;
	while (s[count] != '\0')
	{
		count++;
	}
	return count;
}

int STRICMP(char s1[], char s2[])
{
	/*STRLWR(s1);
	STRLWR(s2);
	return STRCMP(s1, s2);*/
	int length1 = STRLEN(s1);
	int length2 = STRLEN(s2);

	int lengthMin = (length1 < length2) ? length1 : length2;
	for(int i = 0; i < lengthMin; i++)
	{
		char temp1 = s1[i];
		char temp2 = s2[i];

		// Quy hết tất cả về ký tự thường
		if(temp1 >= 'A' && temp1 <= 'Z')
		{
			temp1 += 32;
		}
		if(temp2 >= 'A' && temp2 <= 'Z')
		{
			temp2 += 32;
		}

		if( temp1 < temp2)
		{
			return -1;
		}
		else if(temp1 > temp2)
		{
			return 1;
		}
	}
	if (length1 > length2)
	{
		return 1;
	}
	else if (length1 < length2)
	{
		return -1;
	}
	return 0;
}

int main()
{
	char s1[] = "abc";
	char s2[] = "Abc";

	int kq = STRICMP(s1,s2);
	printf("\nKq = %d",kq);

	getch();
	return 0;
}

Line 17: error: conio.h: No such file or directory
In function 'STRICMP':
Line 24: error: 'for' loop initial declaration used outside C99 mode