[C] How do I perform input validation and handle user errors in C?

In C, you can perform input validation and handle user errors using various techniques. Here are a few common approaches:

  1. Check input boundaries: Validate user input against specific boundaries or constraints to ensure it falls within acceptable ranges. For example, if expecting an integer between 1 and 10, check if the input is within this range using conditional statements and prompt the user again if it is not.
1int num;
2do {
3    printf("Enter a number between 1 and 10: ");
4    scanf("%d", &num);
5    if (num < 1 || num > 10) {
6        printf("Invalid input! Please try again.\n");
7    }
8} while (num < 1 || num > 10);
  1. Validate input type: Ensure that the user enters the expected data type. For instance, if expecting an integer, check if scanf successfully reads an integer value. If not, prompt the user again.
 1int num;
 2int validInput = 0;
 3do {
 4    printf("Enter an integer: ");
 5    validInput = scanf("%d", &num);
 6    if (!validInput) {
 7        printf("Invalid input! Please enter an integer.\n");
 8        // Clear the input buffer
 9        while (getchar() != '\n') {
10            continue;
11        }
12    }
13} while (!validInput);
  1. Use error codes or return values: If a function you're using returns an error code or specific value to indicate an error, check for that value and handle it appropriately. For example, fgets returns NULL on failure, indicating an error occurred while reading input.
1char buffer[100];
2printf("Enter a string: ");
3if (fgets(buffer, sizeof(buffer), stdin) == NULL) {
4    printf("Error occurred while reading input!\n");
5    // Handle the error
6}
  1. Use error handling functions: Implement your own error handling functions to handle specific cases. For example, you can create a function to display an error message and exit the program gracefully.
 1void handleError(const char* errorMessage) {
 2    printf("Error: %s\n", errorMessage);
 3    exit(1);
 4}
 5
 6int main() {
 7    int age;
 8    printf("Enter your age: ");
 9    if (scanf("%d", &age) != 1) {
10        handleError("Invalid input! Please enter a valid age.");
11    }
12    // Rest of the code
13    return 0;
14}

Overall, the approach you choose depends on the specific requirements of your application. Ensure you provide clear error messages and handle exceptions gracefully to enhance user experience.