Write a program to reverse the words order in a sentence (without using additional space)

ReverseWords.cpp

#include <string>

void swap(char* a, char* b) {
		char temp = *a;
		*a = *b;
		*b = temp;
}

void reverse_chars(char* str, int start, int end) {
	// TODO: add nullptr validation

	while (start < end) {
		swap(&str[start],&str[end]);
		start++;
		end--;
	}
}

void reverse_words(char* str) {
	if (str == nullptr || strlen(str) == 0)
		return;

	int length = strlen(str);

	reverse_chars(str, 0, length-1);

	int start_index = 0;
	int end_index = 0;
	for(int i=0 ; i <= length ; i++) {
		if (str[i] == ' ' || i == length) {
			end_index = i - 1;
			reverse_chars(str, start_index, end_index);
			start_index = i + 1;
		}
	}
}

void test(char* str) {
	printf("Before: %s, ", str);
	reverse_words(str);
	printf("After: %s\n", str);
}

int main() {
	char str[100];

	strcpy(str,"");
	test(str);
	
	strcpy(str,"Aa");
	test(str);

	strcpy(str,"Aa Bb");
	test(str);

	strcpy(str,"Aa Bb Cc");
	test(str);

	strcpy(str,"Aa1 Bb2 Cc3");
	test(str);
}