Thread: Why do I have to press enter key twice the first time I call the function?

Code:

#include <stdio.h>


char getInput(){
    char temp;
    while(temp != EOF && (temp=getc(stdin)) != '\n');
    temp = getc(stdin);
    return temp;
}


void main(){
    char input; 
start:
    input = getInput();
    printf("%c\n",input);
    goto start;
}

Result:

I had to hit enter key twice the first time, but there is no problem on the succeeding input prompts. Why does this happen? Is there a way to fix this? Please, help me. What am I doing wrong?

You could get rid of that while loop in getInput. It looks like that's what's causing the problem.

In main, you should use an explicit loop instead of a label with goto. You probably want to check for EOF in the condition of this loop. If your aim is to discard newlines, you can just check for them here and print if the character is not a newline.

Also getInput should return an int because getc returns an int. getc returns an int in order to always allow you to correctly differentiate a valid char input from EOF. But if all you're really doing in getInput is calling getc, then you might as well call getc directly in main.

Likewise, in main input should be an int.

Change the return type of main to int.

1. main returns int.
2. Don't use goto to jump backwards, pick one of the loops like while, for, do
3. temp is a char, and needs to be an int to store and compare with EOF successfully.
4. you don't initialise temp, so you're comparing with garbage the first time around the loop.
5. you're calling getc twice each time

Code:

#include <stdio.h>


char getInput(){
    int temp;
    while( (temp=getc(stdin)) != EOF && temp == '\n');
    return temp;
}

int main() {
    char input;
    do {
      input = getInput();
      printf("%c\n",input);
    } while ( input != 'q' );
}

> Though, I don't understand why I need to change the main to int when I only want to print the integer and not return any value. Please, tell me why.
Because the standard says that main returns an int.

Originally Posted by C99 Standard

5.1.2.2.3 Program termination
If the return type of the main function is a type compatible with int, a return from the
initial call to the main function is equivalent to calling the exit function with the value
returned by the main function as its argument;
reaching the } that terminates the main function returns a value of 0.
If the return type is not compatible with int, the termination status returned to the host environment is unspecified.

Underneath your actual program is the C runtime, which is the bit of code that runs after the OS has done loading your program, and before your code.
Somewhere in there will be

Code:

result = main();  // call the user program
if ( result ...

If you say void, then there is no return value, and then garbage happens.

Modern compilers will do a return 0 if you say nothing, but to be super sure, you should explicitly state one of the following:
return 0;
return EXIT_FAILURE;
return EXIT_SUCCESS;