c - Strings are not printed in accordance with the way they are allocated

Question

In the code below my first output is coming back with my second string combined with my third.

#include <stdio.h>

int bandNumber;
char colorOne[];
char colorTwo[];
char colorThree[];

int main(void) {
    printf("How many bands??
");
    scanf("%d",&bandNumber);
    if(bandNumber == 3) {
        printf("

Enter your first band color: ");
        scanf("%s",colorOne);
        printf("

Enter your second band color: ");
        scanf("%s",colorTwo);
        printf("

Enter your third band color: ");
        scanf("%s",colorThree);
        printf("

Band One: %s",colorOne);
        printf("

Band Two: %s",colorTwo);
        printf("

Band Three: %s

",colorThree);
    }
}

Can anyone explain the errors and what I can do to correct them?

Answer 1

Errors were not detected because either the warnings of your compiler are not enabled, being ignored or need for a better compiler. This code does not allocate space for data being read.

Simplest solution: used fixed size arrays and limit user input.

#include <stdio.h>

int main(void) {
    char colorOne[80+1];
    printf("How many bands??
");
    ...
    printf("

Enter your first band color: ");
    if (1 != scanf("%80s", colorOne)) Handle_EOForIOError();
    ...
    printf("

Band One: %s",colorOne);
}

A more robust solution would use fgets(). If the OS support getline(), consider that.

int main(void) {
    char colorOne[80+1+1];
    printf("How many bands??
");
    ...
    printf("

Enter your first band color: ");
    if (fgets(colorOne, sizeof colorOne, stdin) == NULL) Handle_EOForIOError();

    // Delete potential ending 

    size_t len = strlen(colorOne);
    if (len > 0 && colorOne[len-1] == '
') colorOne[--len] = 0;
    ...
    printf("

Band One: %s",colorOne);
}

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