Implementation of some string utils

strings.c

void strcpy(const char *src, char *dst);
void strcat(char *src, const char *str);
int strlen(const char *src);

void strcpy(const char *src, char *dst)
{
    for (int i = 0; src[i] != '\0'; i++)
        dst[i] = src[i];
}

void strcat(char *src, const char *str)
{
    char *srcend = &(src[strlen(src)]);
    for (int i = 0; str[i] != '\0'; i++)
        srcend[i] = str[i];
}

int strlen(const char *src)
{
    int sum = 0;
    for (; *src != '\0'; src++)
        sum++;
    return sum;
}