Thread: how to clear screen after short pause

When I run this program the numbers are supposed to display for a short time before screen clears. However the 'short pause' seems to happen before the numbers are displayed, then screen clears as soon as they do display, i.e. too fast for eye to see.

Also I'm using a 'for' loop to clear the screen because 'system("clear");' doesnt seem to work in Xcode.

Code:

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

int main(){
	int iNum1 = 0;
	int iNum2 = 0;
	int iNum3 = 0;
	int iAns1 = 0;
	int iAns2 = 0;
	int iAns3 = 0;
	int iCurrentTime = 0;
	int iElapsedTime = 0;
	int iRand = 0;
	int iCount = 0;
	char cYesorNo = '\0';
	int x = 0;
	
	srand(time(NULL));
	
	printf("\nPlay a Game YES (y) or NO (n): \n");
	scanf("%c", &cYesorNo);
	
	if (cYesorNo == 'Y' || cYesorNo == 'y') { //if1
		
		iNum1 = rand() % 100 + 1;
		iNum2 = rand() % 100 + 1;
		iNum3 = rand() % 100 + 1;
		
		printf("\nConcentrate on these 3 numbers:\n");
		printf("%d %d %d", iNum1, iNum2, iNum3);
		
		iCurrentTime = time(NULL); //
		
		do { // do1
			iElapsedTime = time(NULL);
		} while ((iElapsedTime - iCurrentTime) < 3); // do1
		
		//system ("clear");
		for (x = 0; x < 100; x++) {
			printf("\n");
		}
		
		printf("\nEnter the #'s, with a space between each one: \n");
		scanf("%d %d %d", &iAns1, &iAns2, &iAns3);
		
		if (iNum1 == iAns1 && iNum2 == iAns2 && iNum3 == iAns3) { // if 2
			printf("\n*** CONGRATULATIONS ***\n");
					}// if2
		else {//else1
			printf("\nSorry, the correct numbers were %d %d %d", iNum1, iNum2, iNum3);
			}//else2

	}//if1
	return 0;
}//main

cheers Salem

So fflush(stdout); - clears the output buffer and ensures the output is printed to the screen asap?

Now the time countdown works (output stays on screen for about 3 seconds) before the "clear" command starts.

My question are,
1. before I added the fflush, why did the output wait a few seconds before appearing on screen (I have never seen this before with a simple printf command)?
2. Why didn't the time delay do..while loop work before fflush was added above it?

Thanks for the help.

Originally Posted by dunsta

So fflush(stdout); - clears the output buffer and ensures the output is printed to the screen asap?

Now the time countdown works (output stays on screen for about 3 seconds) before the "clear" command starts.

My question are,
1. before I added the fflush, why did the output wait a few seconds before appearing on screen (I have never seen this before with a simple printf command)?
2. Why didn't the time delay do..while loop work before fflush was added above it?

Thanks for the help.

Just as what you type at the keyboard doesn't get passed to the system until you press enter-key, what the program types to the console doesn't get passed to the system until your program "presses enter-key" by printing a \n character or by doing fflush. (EDIT: Of course, this is a very large over-simplification, but it's the general idea.)

And your compiler should have options to switch between buffered (will wait), and unbuffered (prints right away).

As a student, you'll enjoy the unbuffered style, much more. Good to understand the buffered type, however.

I retyped the program and can't figure out why, after the user enters the 3 numbers and hits (enter) key, I get a windows error message pop-up

"Concentration game.exe has encountered a problem and needs to close. We are sorry for the inconvenience."

Code:

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

int main(){
	int x = 0;
	int iNum1 = 0;
	int iNum2 = 0;
	int iNum3 = 0;
	int iAns1 = 0;
	int iAns2 = 0;
	int iAns3 = 0;
	int iCurrentTime = 0;
	int iElapsedTime = 0;
	char YesOrNo = '\0';

	srand((unsigned)time(NULL));

		printf("\t***********************************\n");
		printf("\t*     A GAME OF CONCENTRATION     *\n");
		printf("\t***********************************\n");
		printf("\n\tWould you like to play a game ('Y' or 'N') ?: ");
		scanf("%c", &YesOrNo);

		if (YesOrNo == 'y' || YesOrNo == 'Y'){//if1
						
				
				iNum1 = ((unsigned)rand()) %100 + 1;
				iNum2 = ((unsigned)rand()) %100 + 1;
				iNum3 = ((unsigned)rand()) %100 + 1;
				printf("Watch the 3 numbers closely.\n");
				printf("\n\n%d %d %d\n", iNum1, iNum2, iNum3);
				fflush(stdout);

				iCurrentTime = ((unsigned)time(NULL));

				do{
					iElapsedTime = ((unsigned)time(NULL));
				}while((iElapsedTime - iCurrentTime) <2);

				system("cls");
				//for(x=0;x<100;x++){
				//	printf("\n");
				//}

				printf("Enter the 3 numbers with a space in between: \n");
				scanf("%d %d %d", &iAns1, iAns2, iAns3);
				if (iAns1 == iNum1 && iAns2 == iNum2 && iAns3 == iNum3){//if2
					printf("\n\n\t\tCONGRATULATIONS!\n");
				}//if2

				else{	//else2
					printf("\nSorry, the correct answers were %d %d %d", iNum1, iNum2, iNum3);
				}//else2

		
		}//if1
		/*else {
			printf("GOODBYE");
		}*/

		return 0;

}//main

I compared it to my code in post 1 and can't find why code in post 1 works, but the new one doesn't??

Thanks for any help.

oh man!



Thanks

now after I have added a loop, the program runs once, but then after the loop, runs twice, then waits for user input?

Code:

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

int main(){
	int x = 0;
	int iNum1 = 0;
	int iNum2 = 0;
	int iNum3 = 0;
	int iAns1 = 0;
	int iAns2 = 0;
	int iAns3 = 0;
	int iCurrentTime = 0;
	int iElapsedTime = 0;
	char YesOrNo = '\0';

	srand((unsigned)time(NULL));

	
		
	do {
		printf("\n\t***********************************\n");
		printf("\t*     A GAME OF CONCENTRATION     *\n");
		printf("\t***********************************\n");
		printf("\n\tWould you like to play a game ('Y' or 'N') ?: ");
		scanf("%c", &YesOrNo);

		if (YesOrNo == 'y' || YesOrNo == 'Y'){//if1
						
				
				iNum1 = ((unsigned)rand()) %100 + 1;
				iNum2 = ((unsigned)rand()) %100 + 1;
				iNum3 = ((unsigned)rand()) %100 + 1;
				printf("Watch the 3 numbers closely.\n");
				printf("\n\n%d %d %d\n", iNum1, iNum2, iNum3);
				fflush(stdout);

				iCurrentTime = ((unsigned)time(NULL));

				do{
					iElapsedTime = ((unsigned)time(NULL));
				}while((iElapsedTime - iCurrentTime) <2);

				system("cls");
				//for(x=0;x<100;x++){
				//	printf("\n");
				//}

				printf("Enter the 3 numbers with a space in between: \n");
				scanf("%d %d %d", &iAns1, &iAns2, &iAns3);
				if (iAns1 == iNum1 && iAns2 == iNum2 && iAns3 == iNum3){//if2
					printf("\n\n\t\tCONGRATULATIONS!\n");
				}//if2

				else{	//else2
					printf("\nSorry, the correct answers were %d %d %d\n", iNum1, iNum2, iNum3);
				}//else2

		
		}//if1

		else if  (YesOrNo == 'n' || YesOrNo == 'n'){
				
					printf("\nGOODBYE\n");
					break;
						}
	
	}while(1);

		return 0;

}//main

I tried to understand the article as best as I could, but some of it is a bit over my head at the moment. The code I thought might help, didn't. I assume I am using it wrong, or I'm way off. But I still get the "would you like ??" offered twice.

Code:

printf("\n\tWould you like to play a game ('Y' or 'N') ?: ");
		scanf("%c", &YesOrNo);
		//fgets(YesOrNo, 2, stdin);
		while (scrap != '\n') scrap = getchar();

Code:

	printf("Enter the 3 numbers with a space in between: \n");
	scanf("%d %d %d", &iAns1, &iAns2, &iAns3);

Try here.

I entered the scrap newline loop after the user enters the 3 answers, but sometimes the "Would you like..." appears only once on the first iteration, but then runs through twice after selecting a new game??

Code:

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

int main(){
	int scrap = 0;
	int iNum1 = 0;
	int iNum2 = 0;
	int iNum3 = 0;
	int iAns1 = 0;
	int iAns2 = 0;
	int iAns3 = 0;
	int iCurrentTime = 0;
	int iElapsedTime = 0;
	char YesOrNo = '\0';
	//char YesOrNo[2];
	
	srand((unsigned)time(NULL));
	
	
	
	do {
		printf("\n\t***********************************\n");
		printf("\t*     A GAME OF CONCENTRATION     *\n");
		printf("\t***********************************\n");
		printf("\n\tWould you like to play a game ('Y' or 'N') ?: ");
		scanf("%c", &YesOrNo);
		//fgets(YesOrNo, 2, stdin);
		while (scrap != '\n') scrap = getchar();
		
		if (YesOrNo == 'y' || YesOrNo == 'Y'){//if1
			
			
			iNum1 = ((unsigned)rand()) %100 + 1;
			iNum2 = ((unsigned)rand()) %100 + 1;
			iNum3 = ((unsigned)rand()) %100 + 1;
			printf("Watch the 3 numbers closely.\n");
			printf("\n\n%d %d %d\n", iNum1, iNum2, iNum3);
			fflush(stdout);
			
			iCurrentTime = ((unsigned)time(NULL));
			
			do{
				iElapsedTime = ((unsigned)time(NULL));
			}while((iElapsedTime - iCurrentTime) <2);
			
			system("cls");
			//for(x=0;x<100;x++){
			//	printf("\n");
			//}
			
			printf("Enter the 3 numbers with a space in between: \n");
			scanf("%d %d %d", &iAns1, &iAns2, &iAns3);
			
			while(scrap != '\n') scrap = getchar();
			
			if (iAns1 == iNum1 && iAns2 == iNum2 && iAns3 == iNum3){//if2
				printf("\n\n\t\tCONGRATULATIONS!\n");
				
			}//if2
			
			else{	//else2
				printf("\nSorry, the correct answers were %d %d %d\n", iNum1, iNum2, iNum3);
			
			}//else2
			
			
		}//if1
		
		else if  (YesOrNo == 'n' || YesOrNo == 'n'){
			
			printf("\nGOODBYE\n");
			break;
		}
		
	}while(1);
	
	return 0;
	
}//main