How to change newline character with one space when concatenating strings in C?

Question

Firstly, i must mention that i'm just learning about strings in C as a beginner. What i want to do is get 2 strings as input from an user and concatenate them. So here's what i did:

char firststring[40], secondstring[40];

printf ("Enter first string: ");
fgets (firststring, 40, stdin);
printf ("Enter second string: ");
fgets (secondstring, 40, stdin);

strcat(firststring, secondstring);
printf("%s", firststring);

The problem is that fgets also reads the newline character when the user inputs the first string so the output looks like this:

Hello World

I tried to use puts instead of fgets and it worked well, but too many people said NOT to use that function. Then i found out that i can use strcspn after the first fgets to remove the newline character, but that didn't gave me the one space i want between the words. Desired output: Hello World What i got: HelloWorld

Any suggestions how to do that?

Answer 1

You can do the following way

printf ("Enter first string: ");
fgets (firststring, 40, stdin);
printf ("Enter second string: ");
fgets (secondstring, 40, stdin);

size_t n = strcspn( firststring, "\n" );
firststring[n] = ' ';
strcpy( firststring + n + 1, secondstring );

provided that the firststring has enough space to append the string stored in the array secondstring.

Here is a demonstrative program

#include <stdio.h>
#include <string.h>

int main(void) 
{
    enum { N = 40 };
    char firststring[N], secondstring[N];

    printf( "Enter first string: " );
    fgets( firststring, N, stdin );

    printf( "Enter second string: " );
    fgets( secondstring, N, stdin );

    size_t n = strcspn( firststring, "\n" );
    firststring[n] = ' ';

    strcpy( firststring + n + 1, secondstring );

    puts( firststring );

    return 0;
}

Its output might look like

Enter first string: Hello
Enter second string: World!
Hello World!

A general approach to remove the new line character from a string entered by a call of fgets is the following

string[ strcspn( string, "\n" ) ] = '\0';