CODEWITHSUNDEEP
cwindowsprintfscanf
Ilan Aizelman WS
Ilan Aizelman WS

Reputation: 1632

Why printf() is not used when scanf returns negative number?

I have written a code which checks when scanf() returns a negative number, for example if I press "Ctrl+Z" it should get out of the while loop and printf("Finish!") , but instead it is not printing the "finish!" can anybody take a look?

#include <stdio.h>
#include <conio.h>
#include <math.h>

#define G 9.81

float Height(float speed, float angle, float time);
float Horizontal(float speed, float angle, float time);


void main()
{
    float speed;
    float angle;
    float time = 0.1;
    float height = 0;
    float horizontal = 0;
    int res = 0;

    printf("Enter v <0.0 - 100.0 m/s> and a <0-90 degrees>: ");
    res = scanf_s("%f %f", &speed, &angle);
    while (res != -1)
    {
        for (time = 0.1; height >= 0; time += 0.1)
        {
            printf("Time: %.1f .... H = %.2f  S = %.2f \n", time, horizontal = Horizontal(speed, angle, time), height = Height(speed, angle, time));
        }
        height = 0;
        printf("Fallen!\n");
        printf("Enter v <0.0 - 100.0 m/s> and a <0-90 degrees>: ");
        res = scanf_s("%f %f", &speed, &angle);
    }
    printf("\nFinish!\n");
    getch();
}

float Height(float speed, float angle, float time)
{
    float height;
    angle = ((3.14 / 180) * angle);
    height = (speed * sin(angle) * time) - ((G*time*time) / 2);

    return height;
}

float Horizontal(float speed, float angle, float time)
{
    float horizontal;
    angle = ((3.14 / 180) * angle);
    horizontal = (speed * cos(angle)) * time;

    return horizontal;
}

I'm using Visual Studio (C language) on Windows.

Upvotes: 1

Views: 255

Answers (3)

nnn
nnn

Reputation: 4220

Be sure to press Enter after Ctrl+Z. By default, the terminal input is line-buffered, and it is passed to the program when newline is encountered.

Also, most probably you are running the program in a separated terminal window, which closes when the program exits. This would explain the need for getch(); at the end, to be able to see the output, and then close the window with a keypress.

By default, printf is buffered and the output is written to the terminal when newline \n is reached. The buffer is also flushed when the program exits (exit call or main return). In your case, it will be printed after you press a key, and you may not be able to see it, because the window closed.

To solve this, add a newline character at the end:

printf("\nFinish!\n");

Upvotes: 0

J91321
J91321

Reputation: 727

I believe it should work. Even with >= in while. Definitely works on unix with ordinary scanf().

What IDE and compiler are you using? Are you running this directly through cmd.exe? I'd suggest checking Having troubles with EOF on Windows 7 Also as mentioned in other answers add:

printf("\nFinish!\n");

Upvotes: 0

Christophe
Christophe

Reputation: 73376

Here the reference for scanf(): http://www.cplusplus.com/reference/cstdio/scanf/

When scanf() encounters end of file (that's the usual meaning of ctrl+z on the console), it is not a matching error: it's only that a part of the expected items could be read.

Make your while use >0 instead of >=0.

Upvotes: 1

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