Strcat Function In C++

[Kamalsharma]

I'm new to C and C++ programming, can anyone give me a hint on what I'm doing wrong here. I'm trying to write to concat function that takes to pointers to chars and concatenates the second to the first. The code does do that, but the problem is that it adds a bunch of junk at the end.

For instance, when passing the arguments - "green" and "blue", the output will be "greenblue" plus a bunch of random characters. I also wrote the strlen function that strcat uses, which I will provide below it for reference. I'm using the online compiler at

###### The link given is false, it has been suppressed
and specification is this:

int main(int argc, char** argv)
{
const int MAX = 100;

char s1[MAX];
char s2[MAX];

cout << "Enter your first string up to 99 characters. ";
cin.getline(s1, sizeof(s1));
int size_s1 = strlen(s1);
cout << "Length of first string is " << size_s1 << "\n";

cout << "Enter your second string up to 99 characters. ";
cin.getline(s2, sizeof(s2));
int size_s2 = strlen(s2);
cout << "Length of second string is " << size_s2 << "\n";
cout << " Now the first string will be concatenated with the second
string ";
char* a = strcat(s1,s2);

for(int i = 0; i<MAX; i++)
cout <<a[i];

// system("pause");
return 0;
}

//strcat function to contatenate two strings
char* strcat(char *__s1, const char *__s2)
{
int indexOfs1 = strlen(__s1);
int s2L = strlen(__s2);
cout <<s2L << "\n";
int indexOfs2 = 0;
do{
__s1[indexOfs1] = __s2[indexOfs2];
indexOfs1++;
indexOfs2++;
}while(indexOfs2 < s2L);


return __s1;
}

//Returns length of char array
size_t strlen(const char *__s)
{
int count = 0;
int i;
for (i = 0; __s[i] != '\0'; i++)
count++;
return (count) / sizeof(__s[0]);

}

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[gienas]

Hello Kamalsharma and everybody

Welcome on Futura forums.

I'm new to C and C++ programming . .

1- the langage to be used on the forum is only French. May be no future response;

2- it's not a technology queestion, it will be placed on the correct section, about programming;

3- you used a link non valid which has been suppressed.

[umfred]

pourquoi réécrire une fonction qui existe déjà ? https://www.cplusplus.com/reference/cstring/strcat/
potentiellement, il y a un problème de taille des chaines; sinon une chaine se termine toujours par un caractère nul \0; ce que tu as "oublié" de faire après ta boucle.