Is the initialization of the empty char array valid? - c++

Question

int main()
{
cout<<"Enter a word"<<endl;
char word1[]={0}; //first char array initialization
cin>>word1;
cout<<"Enter another word"<<endl;
char word2[]={0}; //second char array initialization
cin>>word2;
char word3[]={0};
char word4[]={0};
int i=0;
while (word1[i]!='\0') //this converts both words to lower case by usinction tolower
{
word3[i]=char(tolower(word1[i])); //word3 and word4 stores the new arrays
word4[i]=char(tolower(word2[i]));
i++;
}
int output; //output stores the value of 0,1 or -1
output=compareString(word3,word4);
if (output==0)
{
cout<<"The two words are the same."<<endl; //if arrays are same
}
if (output==1)
{
cout<<"the 1st character of 1st word has a larger value than of 2nd word."<<endl;
}
if (output==-1)
{
cout<<"the 1st character of 2nd word has a larger value than of 1st word."<<endl;
}
return 0;
}
int compareString(char string1,char string2)
{
int size1=0; //initialize size of string1
int j=0; //string1 position initialize
while (string1[j]!='\0') //loop to determine size of string1
{
size1+=1;
j+=1;
}
int a=0; //initialize size of string2
int size2=0; //string2 position
while (string2[a]!='\0') //loop determines size of string2
{
size2+=1;
a+=1;
}
int i=0;
int k=0;
for (i=0;i<size1;i++) //loop to compare the two strings
{
if (string1[i]!=string2[i])
{
if (string1[i]>string2[i]) //comparing 1st character of string1 & string2
{
return 1;
}
else //if string2's first character is greater in value
{
return -1;
}
}
else
{
k++; //incrementing k when character of string1 matches string2 character
}
}
if (k==size1) //to cjheck if all characters of both strings are same
{
if (k==size2)
{
return 0;
}
}
}
This is a function which compares two char arrays and returns 0 if characters correspond to each other,returns 1 if first character of string1 is greater than first character of string2 in value and returns -1 if first character of string1 is less than first character of string2.The problem is that when i run it,even when the two words are different,the output is always 0 and the text "The words are the same" appears.
Am i initializing the two arrays correctly in my main program?or is there some other problem?

Answer 1

This declaration
char word1[]={0};
declares an array of size 1, meaning when you do your input it will overwrite the stack. The same for all other arrays.
When dealing with string in C++ it is highly recommended to use std::string!

Answer 2

char word1[]={0};
This line creates an array word1 that has exactly one element, set to 0. When using this array to hold a string, you cannot hold anything in this except the empty string. You are causing a buffer overflow here, because you read a non-empty string into this array, which will then write into other parts of memory not allocated to this array. This is very bad.
Consider using std::string to hold strings instead. It will automatically resize its allocation as necessary.