recurive.c

#include <stdio.h>

int mystrlen(char *a) {
	if (*a == 0)
		return 0;
	else
		return 1 + mystrlen(a + 1);
}

void strreverse(char *a, int b, int c) {
	if (c < 0)
		return;
	char temp;
	temp = *(a + c);
	*(a + c) = *(a + b - c - 1);
	*(a + b - c - 1) = temp;
	strreverse(a, b, c - 1);
}

int myadd(int a, int b) {
	if (b < 0)
		return 0;
	return a + myadd(1, b - 1);
}

int mymult(int a, int b) {
	if (b == 0)
		return 0;
	return a + mymult(a, b - 1);
}

int gcd(int a, int b) {
	if (a == 0)
		return b;
	return gcd(b % a, a);
}

int lcm(int a, int b) { return a * b / gcd(a, b); }

int main() {
	char a[] = "ABCDEFG";
	printf("mystrlen(a)   : %d\n", mystrlen(a));
	strreverse(a, mystrlen(a), (mystrlen(a) - 1) / 2);
	printf("strreverse(a) : %s\n", a);
	printf("myadd(100,50) : %d\n", myadd(100, 50));
	printf("mymult(50,2)  : %d\n", mymult(50, 2));
	printf("gcd(144,180)  : %d\n", gcd(144, 180));
	printf("lcm(144,180)  : %d\n", lcm(144, 180));
}