不使用strlen（）计算并打印字符串的长度

Question

In this program, I am trying to compute and print the length of string without using strlen(). Why it always prints "length is : 0"

#include <stdio.h>

int length(char str[])
{
    int a_string;
    for (a_string=0;str[a_string]!='\0';++a_string)
    {
        return a_string;
    }
}

int main()
{
    char line[80];
    printf("Enter string:\n");
    fgets(line,sizeof(line), stdin);
    printf("Length (including newline) is: %d\n",length(line));
    return 0;
}

Answer 1

Your return statement is inside the loop, so it exits right away on first iteration. Move it after the loop.

Answer 2

In your for loop, you immediately return a_string which will have a value of 0 the first time. Instead, you should return a_string after the loop completes.

Answer 3

Take the return outside of the for loop. As your code is now, the return is used every iteration of the loop. and this is not what you want. change your code to:

int length(char str[])
{
    int a_string;
    for (a_string=0;str[a_string]!='\0';++a_string)
    {
    }
        return a_string;
}

Now the loop would run and a_string would be equal to the size of the string, and the return would be called only after the loop finishes its run, and not after the first iteration.

Answer 4

not the prettiest variant, but the fastest. however, always use the standard function, it is often written in assembly language for a particular architecture, and most fastest, that you could write on the C

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

size_t my_strlen(char *a)
{
        char *b;
        for (b = a; *a; a++);
        return a - b;
}

int main(void)
{
        char *str = "Hello world";
        printf("str len %d\n", my_strlen(str));
        return 0;
}

in your code your need change

for (a_string=0;str[a_string]!='\0';++a_string)
{
    return a_string;
}

to

    for (a_string=0;str[a_string]!='\0';++a_string)
    {
        ;
    }
return a_string

Answer 5

Another way, without strlen() and without increasing a counter:

int length(char *str)
{
  const char *w = str;

  while(*str)
    str++;

  return str - w;
}

Answer 6

the code should not return until AFTER the calculation is complete.
currently the code returns before ever doing any counting
suggest the following, which you might evaluate to assure the 
returned value does not include the null byte

int length(char* str)
{
    int a_string;
    for (a_string=0; str[a_string]!='\0'; ++a_string);

    return a_string;
}