在C++ int main()的do-while循环中添加退出功能遇阻求助

Hey there, let's get that exit feature working properly for you! I can tell you're on the right track using a bool keepGoing variable with a do-while loop to keep your program running, but the issue with detecting 'q' or "exit" comes down to a few common C pitfalls. Let's break this down and fix it step by step.

The Core Issues You're Facing #

1. Comparing strings with ==: In C, you can't use == to check if two strings are equal—this compares the memory addresses of the char arrays, not their actual content. You need to use the strcmp() function from <string.h> instead.
2. Invalid character constants: Writing 'quit' is a multi-character character constant, which has undefined behavior in C. Strings like "exit" need to be wrapped in double quotes ("exit"), not single quotes.
3. Unprocessed newline characters: If you're using functions like scanf or fgets, they might leave a newline in the input buffer or include it in your input string, which breaks string comparisons.

Working Example Code #

Here's a complete, tested implementation that handles both 'q' (single key press) and "exit" (full string input) to exit the loop:

#include <stdio.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>

int main() {
    bool keepGoing = true;
    char input[256]; // Buffer to store user input (size it appropriately for your use case)

    do {
        // Prompt the user for input or exit options
        printf("Enter your command (type 'exit' or press 'q' to quit): ");

        // Use fgets to safely read input (avoids buffer overflow issues with scanf)
        if (fgets(input, sizeof(input), stdin) == NULL) {
            // Handle unexpected input errors (like EOF from Ctrl+D/Ctrl+Z)
            keepGoing = false;
            break;
        }

        // Remove the trailing newline character added by fgets (if present)
        size_t inputLength = strlen(input);
        if (inputLength > 0 && input[inputLength - 1] == '\n') {
            input[inputLength - 1] = '\0';
        }

        // Check for single 'q' input (case-insensitive, so 'Q' works too)
        if (strlen(input) == 1) {
            char inputChar = tolower(input[0]);
            if (inputChar == 'q') {
                printf("Exiting program via 'q' key...\n");
                keepGoing = false;
                continue;
            }
        }

        // Check for "exit" command (case-sensitive here; make it case-insensitive if needed)
        if (strcmp(input, "exit") == 0) {
            printf("Exiting program via 'exit' command...\n");
            keepGoing = false;
            continue;
        }

        // --------------------------
        // Insert your program's core logic here
        // --------------------------
        printf("Processing your input: %s\n", input);

    } while (keepGoing);

    printf("Program exited successfully!\n");
    return 0;
}

Key Explanations #

• strcmp() for string comparisons: This function returns 0 if the two strings are identical, which is why we check strcmp(input, "exit") == 0.
• Newline handling: fgets reads the newline character when the user presses Enter, so we replace it with a null terminator (\0) to make sure our string comparisons work correctly.
• Case insensitivity (optional): Using tolower() from <ctype.h> lets users press 'Q' instead of just 'q' to exit—remove this if you want case-sensitive behavior.
• Safe input with fgets: Unlike scanf, fgets limits the number of characters read to the size of your buffer, preventing buffer overflow vulnerabilities.

Quick Fixes for Your Existing Code #

If you want to adapt your current code instead of using the full example:

• Replace any if (exitCon == 'quit') lines with if (strcmp(exitCon, "exit") == 0) (make sure exitCon is a char array, not a single char).
• For the 'q' check, verify that your input is a single character first, then compare it to 'q' (or 'Q' if you want case insensitivity).
• Always include the necessary headers: <stdbool.h> for bool, <string.h> for string functions, and <ctype.h> if using tolower().

内容的提问来源于stack exchange，提问作者Michael Musk