gistfile1.c

#include <stdio.h>

#define TEST(a, b, mustBe) \
  if(mustBe != compareString(a, b)) { printf("Error > "); } \
	printf("%s %s %s\n", a, compareString(a, b) ? "==" : "!=", b);

char downcaseChar(char value)
{
	if(value >= 65 && value <= 90)
		value += 32;

	return value;
}

int compareChar(char firstChar, char secondChar)
{
	return downcaseChar(firstChar) == downcaseChar(secondChar);
}

int compareString(char* firstString, char* secondString)
{
	int i = 0;

	for(; ; ++i)
	{
		if(!compareChar(firstString[i], secondString[i]))
			return 0;

		if(compareChar(firstString[i], '\0') && compareChar(secondString[i], '\0'))
			return 1;

		if(compareChar(firstString[i], '\0') || compareChar(secondString[i], '\0'))
			return 0;
	}

	return 0;
}

int main(void)
{
	TEST("Varya", "varya", 1);
	TEST("Varya", "Varya", 1);
	TEST("Varya1", "varya", 0);
	TEST("Varya1", "varya5", 0);
	TEST("I'm superman!", "I'm superman", 0);

	return 0;
}