cant change the character in c - c

Question

I'm learning c and I have a problem with the following code. I want to convert "Hello" to "H*llo". But the code does not work.
The code does not give an error and does not work.
#include <stdio.h>
int length(char *abc){
int i;
for (i = 0; i < abc[i]; i++);
return i;
}
int hideAfromB(char *a, char *b){
int n = 0;
int aLength = length(a);
int bLength = length(b);
for (int i = 0; i < bLength; i++){
if (a[0+n] == b[i]){
n = n + 1;
if (n == aLength){
for (int j = 0; j < aLength; j++)
{
b[i-j] = '*';
}
n = 0;
}
}
else{
n = 0;
}
}
printf("%s",b);
return 0;
}
int main()
{
hideAfromB("e","Hello");
return 0;
}
I need help.
Thanks.

Answer 1

Because the string "Hello" is a constant and you can't change it.
As other have stated, declaring explicitly a char array will sove the problem:
#include <stdio.h>
#include <string.h>
int length(char *abc){
int i;
for (i = 0; i < abc[i]; i++);
return i;
}
int hideAfromB(char *a, char *b){
int n = 0;
int aLength = strlen(a);
int bLength = strlen(b);
for (int i = 0; i < bLength; i++){
if (a[0+n] == b[i]){
n = n + 1;
if (n == aLength){
for (int j = 0; j < aLength; j++)
{
b[i-j] = '*';
}
n = 0;
}
}
else{
n = 0;
}
}
printf("%s",b);
return 0;
}
int main()
{
char t [] = "Hello";
hideAfromB("e",t);
return 0;
}
Link to the fixed code:

Answer 2

The main issue is that the second argument in hideAfromB("e","Hello"); is a constant string which can not be modified.
for (i = 0; i < abc[i]; i++);
This literally iterates through the array until the iterator value is bigger than the value in the array while executing an empty instruction (;).
size_t is the proper type for string length.
You could use strstr to find a single character in a string.
#include <stdio.h>
#include <string.h>
int length(char *abc){
for (int i = 0; i >= 0; i++) {
if (abc[i] == '\0') {
return i;
}
}
return -1; // indicate string end not found
}
int hideAfromB(char *a, char *b){
int n = 0;
size_t aLength = strlen(a); // standard function
int bLength = length(b); // modified own function
for (size_t i = 0; i < bLength; i++){
if (a[n] == b[i]){
n = n + 1;
if (n == aLength){
for (int j = 0; j < aLength; j++)
{
b[i-j] = '*';
}
n = 0;
}
}
else{
n = 0;
}
}
printf("%s\n",b);
return 0;
}
int main()
{
char hello[] = "Hello"; // the elements of the array can be modified
hideAfromB("e", hello);
return 0;
}
$ gcc -Wall compare.c
$ ./a.out
H*llo
$