Question

So I have some code that looks like this:

int a[10]; a = arrayGen(a,9); 

and the arrayGen function looks like this:

int* arrayGen(int arrAddr[], int maxNum) {     int counter=0;     while(arrAddr[counter] != '\0') {         arrAddr[counter] = gen(maxNum);         counter++;     }     return arrAddr; } 

Right now the compilier tells me ‘warning: passing argument 1 of ‘arrayGen’ makes integer from pointer without a cast’

My thinking is that I pass ‘a’, a pointer to a[0], then since the array is already created I can just fill in values for a[n] until I a[n] == ‘\0’. I think my error is that arrayGen is written to take in an array, not a pointer to one. If that’s true I’m not sure how to proceed, do I write values to addresses until the contents of one address is ‘\0’?

Answer 1

The basic magic here is this identity in C:

*(a+i) == a[i] 

Okay, now I’ll make this be readable English.

Here’s the issue: An array name isn’t an lvalue; it can’t be assigned to. So the line you have with

a = arrayGen(...) 

is the problem. See this example:

int main() {     int a[10];      a = arrayGen(a,9);      return 0; } 

which gives the compilation error:

gcc -o foo foo.c foo.c: In function 'main': foo.c:21: error: incompatible types in assignment  Compilation exited abnormally with code 1 at Sun Feb  1 20:05:37 

You need to have a pointer, which is an lvalue, to which to assign the results.

This code, for example:

int main() {     int a[10];     int * ip;      /* a = arrayGen(a,9);  */     ip = a ; /* or &a[0] */     ip = arrayGen(ip,9);      return 0; } 

compiles fine:

gcc -o foo foo.c  Compilation finished at Sun Feb  1 20:09:28 

Note that because of the identity at top, you can treat ip as an array if you like, as in this code:

int main() {     int a[10];     int * ip;     int ix ;      /* a = arrayGen(a,9);  */     ip = a ; /* or &a[0] */     ip = arrayGen(ip,9);      for(ix=0; ix < 9; ix++)         ip[ix] = 42 ;      return 0; } 

---

Full example code

Just for completeness here’s my full example:

int gen(int max){     return 42; }  int* arrayGen(int arrAddr[], int maxNum) {     int counter=0;     while(arrAddr[counter] != '\0') {         arrAddr[counter] = gen(maxNum);         counter++;     }     return arrAddr; }  int main() {     int a[10];     int * ip;     int ix ;      /* a = arrayGen(a,9);  */     ip = a ; /* or &a[0] */     ip = arrayGen(ip,9);      for(ix=0; ix < 9; ix++)         ip[ix] = 42 ;      return 0; }