Use myString.c_str() if you want a C-like string (const char*) to use with printf.

There are multiple problems in the code:

• scanf("[%s\n]", string) does not do what you expect, it reads a character from standard input that must be a [, then reads a space delimited word and stores it to string, then reads and discards the next byte if it is a newline, then reads and discards the next byte if it is a ]. If any of these steps fails, scanf stops and returns the number of valid conversions (0 if the first byte read is not a [ or 1 if a word could be read after the [)

  So if you type 'sam' and hit Enter at the terminal, the conversion will fail immediately because the first byte is not a [ and scanf will return 0, consuming no characters from the input and leaving string unchanged. Since string has automatic storage (a local variable) and was not initialized, it has indeterminate contents, which will look like garbage characters when you print it.

  If you type a [ followed by more than 99 letters, scanf will attempt to store all of them into the string array and cause a buffer overflow when writing beyond the end of this array, invoking undefined behavior. This is a security flaw that could be exploited. To avoid this problem, always specify the maximum number of characters between the % and the s, and do this also for %[ conversions.

  To read a single word from standard input with scanf, you should have used scanf("%99s", string) and checked the return value for success (must be 1). Yet this approach has some drawbacks:

  • you cannot read an empty word: scanf() will return 0 if you just hit the Enter key without any previous input.
  • the rest of the input line, including the newline is left pending in the standard input buffer, which may cause unexpected behavior for further input.
  • the length must be passed as en explicit number: one cannot use sizeof or an expression for the maximum input length, which is at least 1 less than the destination array length, making the code confusing.

  It is recommended to read a full line of input with fgets() or getline() and parse the line with sscanf or custom code.

• printf(string) is very risky! It will have undefined behavior if the string contains printf conversion specifications such as %s that will cause it to retrieve arguments that you did not pass. If you type [%sam at the prompt, the program will likely crash with a segmentation fault.

  Always pass a string literal as the format string and turn on extra warnings (eg: -Wall -Wextra -Werror) to let the compiler verify the consistency of the format string and the arguments actually passed to printf. In this particular case, you should use printf("%s\n", string).

Here is a modified version:

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

int main(void)
{
    char line[100];
    char word[100];
    printf("Please type some input: ");
    if (fgets(line, sizeof line, stdin)) {
        printf("You typed this: %s\n", line);
        if (sscanf(line, "%99s", word) == 1) {
            printf("this is the first word: %s\n", word);
            system("pause");
            return 0;
        } else {
            printf("no word was typed\n");
            system("pause");
            return 1;
        }
    } else {
        printf("invalid or missing input\n");
        system("pause");
        return 1;
    }
}