C语言中我的while循环条件错误的原型函数

Question

How could I run my own prototype function with my while loop condition?

#include <stdio.h>
#include <conio.h>
#include <string.h>

msghere(char *text){
    printf("%s",text);
    return 0;
}
void main(){
    char inp[256]={0};
    clrscr();
    while( strcmp(inp,"pass") && msghere("Error!")){
        memset(inp,0,strlen(inp));
        printf("Type \"pass\": ");
        gets(inp);
    }
    msghere("Right Answer!");
    getch();
}

This code prints an output of:

Error!Right Answer!

Answer 1

What you want is a do-while loop and something like an if condition.

int msghere(char *text){
    printf("%s",text);
    return 1;
}
int main(void)
{    
    do
    {
    //your code
    }while( (strcmp(inp, "pass") == 0 ? 0 : msghere("error!")) );
}

Why the do-while?
Because you want your user to make an input before you check it the first time. Logical right?

WTF is " while( (strcmp(inp, "pass") == 0 ? 0 : msghere("error!")) ) "?
First of all: bad coding style. It is a short version if/else. if the first condition is true return the value after the ? otherwise return the value after :

Why return 1; in msghere()?
Because your do while loop will evaluate if there was an error. Error == True -> do it again.

What you should do:
is something like the following:

// your original msghere
int main(void)
{
  int passed = 0;  //false
  // some code
  while(!passed) //while not passed
  {
    //read input with fgets like said in the comments
    if(strcmp(inp, "pass") == 0)
    {
       passed = 1; // true
    }
    else
    {
      msghere("error");
    }
  }
}

it uses a status variable and is much more easyier to read.

Answer 2

#include <stdio.h>
#include <conio.h>
#include <string.h>

int msghere(const char *text)
{
    printf("%s",text);
    return 1; /* you want 1 instead of 0, because (strcmp != 0) && 1 == true */
}

int main(void)
{
    char inp[256];

    clrscr();
    do {
        printf("Type \"pass\": ");
        fgets(inp, sizeof inp, stdin); /* gets is deprecated, use fgets */
    } while (strcmp(inp, "pass\n") && msghere("Error!"));
    msghere("Right Answer!");
    getch();
    return 0;
}

EDIT:

Why is there \\n after pass in while((strcmp(inp, "pass\\n") && msghere("Error!"))

Because fgets puts an extra \\n at the end of the string, you can skip this new line using:

if (fgets(inp, sizeof inp, stdin) != 0)
{
    size_t len = strlen(inp);

    if (len > 0 && inp[len - 1] == '\n')
        inp[len - 1] = '\0';
    /* ... */
}

Seems that you are using Turbo C or an old compiler, use a modern compiler (eg. MinGW), furthermore:

• There is no need to initialize inp
• There is no need to memset on each iteration
• Functions must return some type (in this case int ) or void
• The const qualifier explicitly declares a data object as something that cannot be changed, use it in order to help the compiler build better code.
• Use int main(void) instead of void main()

Answer 3

The strcmp() function return's an integer less than, equal to, or greater than zero if string1 (or the first n bytes thereof) is found,respectively, to be less than, to match, or be greater than string2.

Therefore your call to strcmp in while loop retuns non-zero value.so, the next condition is evaluated ie, calling the function(msghere) . The function executes, prints the result and returns zero, which makes the condition to be false in while loop.

Now, you know what to do.