Store strings into array of strings with scanf

Question

Trying to store input into array of strings with following code:

#include <stdio.h>
#include <string.h>
int main()
{
    int noOfStrings;
    printf("Enter no of strings: ");
    scanf("%d", &noOfStrings);
    char *string[noOfStrings];
    for(int i=0; i<noOfStrings; i++){
        printf("\nEnter string %d: ", i);
        scanf("%s\n",string[i]);
    }
    return 0;
}
-----------------------------------------------------------------------------
Console:
Enter no of strings: 3                                                                                                   

Enter string 0: abc                                                                                                      

Enter string 1: def                                                                                                      

Enter string 2: ghi                                                                                                      

Segmentation fault (core dumped)                                                                                         


...Program finished with exit code 139                                                                                   
Press ENTER to exit console.
-----------------------------------------------------------------------------

I am not able to figure out why this is failing.

I also Tried following code with fixed size array.

#include <stdio.h>
#include <string.h>
int main()
{
    int noOfStrings;
    printf("Enter no of strings: ");
    scanf("%d", &noOfStrings);
    char string[noOfStrings][5];
    for(int i=0; i<noOfStrings; i++){
        printf("\nEnter string %d: ", i);
        scanf("%s\n",string[i]);
    }
    printf("\nPrinting Stored Strings");
    for(int i=0; i<noOfStrings; i++){
        printf("\nEnter string %d: ", i);
        printf("%s\n",string[i]);
    }
    return 0;
}
-----------------------------------------------------------------------------
Console:
Enter no of strings: 3                                                                                                 

Enter string 0: abc                                                                                                    
def                                                                                                                    

Enter string 1: ghi                                                                                                    

Enter string 2: jkl                                                                                                    

Printing Stored Strings                                                                                                
Enter string 0: abc

Enter string 1: def                                                                                                    

Enter string 2: ghi                                                                                                    


...Program finished with exit code 0                                                                                   
Press ENTER to exit console. 

After entering 1st string ('abc') There was no prompt for 2nd string, so proceeded by entering 'def'. Followed by 2 more strings. Notice that string 'jkl' is not printed.

Please tell me what i am missing in these 2 cases?

Thanks.

Answer 1

In the first case, you're defining an array of pointers:

char *string[noOfStrings];

However, these pointers are uninitialized. When you then attempt to use scanf , you dereference these invalid pointers. Doing so invokes undefined behavior , which in this case causes a crash.

Your second case fixes this by using a 2D array of characters big enough to hold the strings you input. But you get stuck because of your scanf format:

scanf("%s\n",string[i]);

The \\n in the format string matches any number of whitespace characters , so the function won't return until you enter a non-whitespace character. You can fix this by removing \\n from the format string.

scanf("%s",string[i]);