Validating user's input to be a number and not a letter

[adibhatam]

I am currently working on an audio recording program. I ask the user to specify if they'd like to record or playback the recording... [recording -> user input = 1, playback -> user input = 2]. Moreover, I want to ensure the user inputs a number and not a letter. I have used isalpha and isdigit, but my output on the console is completely wrong.

int main() {
	//VARIABLE DECLARATION
	int mode = 0;
	int t = 0; 
	
	FILE *fp; 

	if ((fp = fopen("recording.raw", "r"))==NULL) {
		printf("NO RECORDING EXISTS...\nI WILL RECORD YOUR AUDIO FIRST!\n");
		mode = 1;
	}
	else {
		do {
			printf("Please indicate if you would like to: \nRecord [1]\nPlayback [2]\nUSER CHOICE: ");
			scanf("%d", &mode);
			while (isalpha(mode)) {
				printf("INVALID INPUT!\n");
				printf("Please indicate if you would like to: \nRecord [1]\nPlayback [2]\nUSER CHOICE: ");
				scanf("%d", &mode);
			}
			fclose(fp);
		} while (mode != 1 && mode != 2); 
	}

[Marth]

if its only 1 or 2 you are looking to validate, you could change mode to char and check if it comes back as either 49 or 50 according to the ascii chart.


edit: and i think scanf with a char will only pick up the first digit/char entered so it may not need a length input check.

[Thomas1965]

The problem is that you read the input as an int. When you enter an character the input gets rejected by scanf, the value of mode stays 0 and isalpha is always false.
Better to read the input into a char.

[adibhatam]

I changed it to a char, but now there is a null terminator appended to the end of users input. Now the program recognizes the users input of '1' as '1\0'. Is there a solution to removing the null terminator?

 int main() {
	//OPENING MATLAB ENGINE
	/*Engine *m_pEngine; 
	m_pEngine = engOpen("null");*/

	//VARIABLE DECLARATION
	char mode;
	int t = 0; 
	
	FILE *fp; 

	if ((fp = fopen("recording.raw", "r"))==NULL) {
		printf("NO RECORDING EXISTS...\nI WILL RECORD YOUR AUDIO FIRST!\n");
		mode = 1;
	}
	else {
		do {
			printf("Please indicate if you would like to: \nRecord [1]\nPlayback [2]\nUSER CHOICE: ");
			scanf("%c", &mode);
			fclose(fp);
		} while (mode != 1 && mode != 2); 
	}

[Thomas1965]

A char can only hold one char so there can't be a terminating '\0'.
You need to check while (mode != '1' && mode != '2');

[adibhatam]

Thank you for your help! @Thomas1965
I have one more question...

I have a char variable, and I am attempting to make it into an int. After searching online, people mentioned I should do the following:
char t;
int time = t - '0';
After doing this I get a Run-Time Check failure. What is the reason for this?
Thanks in advance.

  int main() {

	//VARIABLE DECLARATION
	char mode;
	char t; 
	
	FILE *fp; 

	if ((fp = fopen("recording.wav", "r"))==NULL) {
		printf("NO RECORDING EXISTS...\nI WILL RECORD YOUR AUDIO FIRST!\n");
		mode = '1';
	}
	else {
		do {
			printf("Please indicate if you would like to: \nRecord [1]\nPlayback [2]\nUSER CHOICE: ");
			scanf("%s", &mode);
			fclose(fp);
		} while (mode != '1' && mode != '2'); 
	}

	if (mode == '1') {
		do {
			printf("Please enter the duration of the recording [SECONDS]: ");
			scanf("%s", &t);
		} while (isalpha(t)); 
	}
	else {
		do {
			printf("Please indicate the duration of the playback [SECONDS]: ");
			scanf("%s", &t);
		} while (isalpha(t)); 
	}
	
	int time = t - '0'; 

	int size = (FREQUENCY * (int)time); 
	char *data = malloc(sizeof(char)*size);			//allocating memory

	if (mode == '1') {
		printf("Recording..."); 
		
		int user_input = 0; 

		Audio_Recording(data, size); 

		printf("Processing...\r"); 

		printf("Saving...\r"); 
		FILE *fp = fopen("recording.wav", "w"); 
		fwrite(data, sizeof(char), size, fp); 

		fclose(fp); 
	}
	else {
		printf("Playing...\r"); 
		FILE *fp = fopen("recording.wav", "r"); 
		fread(data, sizeof(char), size, fp); 

		fclose(fp); 

		Playback_Recording(data, size); 
	}
	free(data); 

	system("PAUSE"); 
	return 0; 
}