【c语言】字符串替换空格：请实现一个函数，把字符串中的每一个空格替换成“％20”

//  字符串替换空格：请实现一个函数，把字符串中的每一个空格替换成“％20”。
//  比如输入“we are happy.”，则输出“we%20are%20happy.”

#include <stdio.h>
#include <assert.h>

char*  replace(char* p)
{
	char* ret = p;
	int num = 0;
	int oldlen = 0;
	int newlen = 0;
	char* q = p;
	char* r;
	assert(p != NULL);
	while (*p != '\0')
	{
		if (*p == ' ')
		{
			num++;
		}
		oldlen++;
		p++;
	}
	p = q;
	newlen = oldlen + 2 * num;
	q = p + oldlen - 1;
	r = p + newlen - 1;
	while (q != r)
	{
		if (*q == ' ')
		{
			*r-- = '0';
			*r-- = '2';
			*r-- = '%';
		}
		else
		{
			*r = *q;
			r--;
		}
		q--;
	}
	return ret;
}

int main()
{
	char p[20] = "we are happy.";
	printf("原字符串是：%s\n", p);
	printf("替换后的字符串是：%s\n", replace(p));
	return 0;
}

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