How to assign array to an array variable

[High Voltage]

Problem text :

Load a string ,which certainly can't be longer than 30 characters . If the loaded series
contains some characters other than uppercase and lowercase letters of the English alphabet and digits 0-9 , print
Message : loaded string not properly entered.
If an array is properly entered, it is necessary to amend a series so that the lowercase a, e , and substitute with
numbers 9,8,7 in the order given .
Print original , and the resulting string .

For example , the input string UlazniNizOd20Znakova prints:


UlazniNizOd20Znakova Ul9zn7NIZOd20Zn9kov9

#include <stdio.h>
#include <conio.h>


int main(){
	
	char string[30+1];
	int i;
	
	scanf("%s", &string);
	
	for( i = 0; string[i] != '\0'; i++){
		
		if( !(string[i] >= '0' && string[i] <= '9'  || string[i] >= 'a' && string[i] <= 'z' || string[i] >= 'A' && string[i] <= 'Z') ){
			printf("Loaded string is not properly entered.");
		}
		
	}
	char changedString[30+1] = string; 
	
	for( i = 0; i < 31; i++){
		
		if(string[i] == 'a'){
			string[i] = '9';	
		}else if(string[i] == 'b'){
			string[i] = '8';
		}else if( string[i] == 'c'){
			string[i] = '7';
		}
	}
	printf("Unchanged string: %s\n", string);
	printf("Changed string: %s", changedString);


}

How to assign array to an array variable,
and why my approach won't work ( guess it has to do something with adresses of the variables)
I assume that in this kind of problems we use pointers but I just started learning about the pointers so I am not so practical with using them yet.

[laserlight]

This:

scanf("%s", &string);

should have been:

scanf("%30s", string);

Remember, when passed as an argument, an array is converted to a pointer to its first element. Furthermore, the 30 in the format specification avoids buffer overflow. You should also check the return value of scanf.

Next:

char changedString[30+1] = string;

You can initialise an array with an initialiser, but not with another array. You can assign to the elements of an array of non-const elements, but you cannot assign to an array. Therefore, you should do something like:

char changedString[30+1] = "";
strncat(changedString, string, 30)

Though you should then #include <string.h>

[High Voltage]

char changedString[30+1] = "";
strncat(changedString, string, 30)

When initializing array variable 'changedString[30+1]' why do I have to put "" sign ?

[Salem]

Firstly, initialisation is different from assignment.

Secondly,

char s[] = "hello";

is just a syntactic sugared version of

char s[] = { 'h', 'e', 'l', 'l', 'o', '\0' };