Turning a simple python "program" in a C "program"!

Question

So i have this "program" in python3 which adds 3 strings but the middle part x times. But i decided to choose C as my first language after doing some simple stuff on Python 3. NOW this is how it looks in Python:

def printWord(begin, mid, end, r):
    print(begin, end="")
    for i in range(r+1):
        print(mid, end="")
    print(end)
begin = input("Enter your beginning.\t")
mid =input("Enter your middle.\t")
end = input("Enter your ending.\t")
r = int(input("How many times?\t"))

printWord(begin, mid, end, r)

So this works and every thing is cool!

Now C:

#include <stdio.h>
#include <stdlib.h>

int makeWord(char begin[], char mid[], char end[], int r)
{
    int i;
    printf("%s", begin);
    for(i=0;i<=r;i++){
        printf("%s", mid);
    }
    printf("%s", end);
    return 0;
}

int main()
{
    int r;
    char begin[3], mid[2], end[3];
    printf("Enter the beginning!\t");
    scanf("%s", begin);
    printf("Enter the middle!\t");
    scanf("%s", mid);
    printf("Enter the ending!\t");
    scanf("%s", end);
    printf("How many times?\t");
    scanf("%d", r);

    makeWord(begin, mid, end, r);

    return 0;
}

But this one stops

Now my question WHY? Thanks for answering

Notice `begin` and `end` can only hold 2 character plus the null-terminator, and `mid` can only hold 1 character. Because you are not controlling how many characters the user can input, this application is prone buffer overflow and crash. — Havenard, Feb 28 '17 at 17:55
Well, theres `scanf_s()` that lets you specify the capacity of your buffer, but it's not defined in the C standard until C11. The compiler `gcc` supports using `scanf()` with null pointer so it allocates the buffer for you, but that's not defined in the C standard either. I'm not entirely sure how to make `scanf()` safe to use. Escape to C++ if you can. — Havenard, Feb 28 '17 at 18:05
http://stackoverflow.com/questions/1787892/overflow-over-scanf8s-string — Havenard, Feb 28 '17 at 18:16

score 1 · Answer 1 · answered Feb 28 '17 at 17:50

You're misusing scanf. It takes pointers to the target variables, while you're passing the variables themselves - look at the documentation online.

This causes all of your variables to be uninitialized and contain garbage values - using them is therefore undefined behavior.

Turning a simple python "program" in a C "program"!

1 Answers1