字符串中空格替换(C语言实现)

题目： 请实现一个函数，把字符串中的每个空格替换成 "%20"。 例如，输入 "We are happy.", 则输出 "We%20are%20happy." 。

char formatBlank(char arr[])
{
    if(arr == NULL)
    {
        return 0;
    }

    int originLength = 0;
    int blankLength = 0;
    int newLength = 0;
    int i = 0;

    while(arr[i] != '\0')
    {
        originLength ++;

        if(arr[i] == ' ')
        {
            blankLength ++;
        }

        i ++;
    }

    newLength = originLength + blankLength * 2;

    for(int j = originLength; j > 0 ; j--)
    {
        if(arr[j] != ' ')
        {
            arr[newLength--] = arr[j];
        }else {
            arr[newLength--] = '0';
            arr[newLength--] = '2';
            arr[newLength--] = '%';
        }
    }

    return 0;
}