Sunday, October 24, 2021

[SOLVED] Why did the two prompts in this program to receive input show on the same line?

Issue

I have a problem when getting input from the user. I used the scanf function to get the input from the user, which I think is the cause of the problem.

I want the two prompts to be on separate lines.

The following code is a simple example of the problem:

#include <stdio.h>
int main(void)
{
    char name[20];
    int age = 0;
    int index;

    printf("1- Insert a new student.\n");
    printf("2- Delete a student.\n");
    printf("3- Show all students.\n");
    printf("4- Exit.\n\nChoose: ");
    scanf("%d", &index);

    printf("Enter your name: ");
    scanf("%20[^\n]s", name);
    //fgets(name, 20, stdin); // <--- Does the same thing.

    printf("Enter your age: ");
    scanf("%d", &age);

    printf("Name: %s, Age: %d\n", name, age);
    return 0;
}

The result as text:

1- Insert a new student.
2- Delete a student.
3- Show all students.
4- Exit.

Choose: 2
Enter your name: Enter your age:

An image:

Why did the two prompts show on the same line?


Solution

I suggest you change this:

scanf("%20[^\n]s", name);

to this:

scanf(" %19[^\n]", name);

for these reasons:

  • The buffer size you specify to scanf does not include the final NUL terminator (unlike with fgets).

  • The previous scanf left a newline in the input buffer, and the format specifiers %[] and %c do not automatically filter it (unlike %d and other specifiers). Adding the space tells scanf to filter it.

  • The final s is not part of the format %[] but is a frequent mistake by coders who have used %s.

Note too, that scanf with %[] is not equivalent to fgets(), which reads any final newline and places it in the buffer supplied.



Answered By - Weather Vane
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