C語言之字元串操作

1.字元串的複制

char *Mystrcpy(const char *source, char *target, int n)
{
    int i = ;
    while(source[i] != '\0')
        i++;
    if(i <= n)
    {
        i = ;
        while(source[i] != '\0')
        {
            target[i] = source[i];
            i++
        }
        target[i] = '\0';
    }
    else
        return NULL;
    return target;
}
           

2.字元串的合并

• 将str2合并到str1中

char *Mystrcat(char *str1, int len, char *str2)
{
    int m =, n = ;
    while(str1[m] != '\0')
    {
        m++;
    }
    while(str2[n] != '\0')
    {
        n++;
    }
    while((m+n-) > len)
    {
        return NULL;
    }
    k = ;
    while(str2[n] != '\0')
    {
        str1[m] = str2[n];
        i++;
        n++;
    }
    str1[n] = '\0';
    return Mystrcat;
}
           

• 将str1與str2合并到target中

char *Mystrcat(char *str1, char *str2, char *target)
{
    int m = , n = ;
    while(str1[m] != '\0')
    {
        target[m] = str1[m];
        m++;
    }
    while(str2[n] != '\0')
    {
        target[m] = str2[n];
        n++;
        m++;
    }
    target[m] = '\0';
    return target;
}
           

3.字元串大小寫轉換

• 大寫轉小寫

char *str2low(const char *source, char *target, int len)
{
    int m = ;
    while(source[m] != '\0')
        m++;
    if (m >= len)
        return NULL;
    else
    {   
        m = 
        while(source[m] != '\0')
        {
            if(source[m] >= 'A' && source[m] >= 'Z')
            {
                target[m] = source[m] + ; 
            }
            else
                target[m] = source[m];
            m++;
        }
        target[m] = '\0';
    }
    return ratget;
}
           

• 小寫轉大寫

在上面的基礎上更改
if(source[m] >= 'a' && source[m] >= 'z')
{
    target[m] = source[m] - ; 
}
           

• 按位操作進行大小寫轉換
• 要保證source與target都是字元，target比source大

大寫轉小寫
A:  ->
a:  ->
按位或運算 ->
           

char *Mystr2lowaw(char *source, char *target)
{
    int n = ;
    while(source[n] != '\0')
    {
        target[n] = source[n] | ;
        n++;
    }
    target[n] = '\0';
    return target;
}
           

小寫轉大寫
A:  ->
a:  ->
按位與運算 ->
           

char *Mystr2highaw(char *source, char *target)
{
    int n = ;
    while(source[n] != '\0')
    {
        target[n] = source[n] & ;
        n++;
    }
    target[n] = '\0';
    return target;
}
           

4.字元串的比較

• 比較兩個字元串是否相同
• 相同傳回0，不同傳回-1

int Mystrcmp(char *str1, char *str2)
{
    int n = ;
    while(str1[n] != '\0')
    {
        if(str1[n] != str2[n])
        {
            return -;
        }
        n++;
    }
    if(str1[n] != str2[n])
        return -;
    return ;
}