Week04--newLecture2

# A local variable containing an address by using this

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Unformatted text preview: i++) sum += *(px+i); sum += x[i]; 18 Pointers and Arrays (cont’d) Recall that the name of an array is the address of the iniCal element of the array. • Thus these two assignments are equivalent: – py = &amp;y[0]; py = y; However, there is one diﬀerence between a pointer (py) and an array name (y): • – A pointer is a variable, thus py++ and py = y are legal statements – An array name is not a variable, thus y++ and y = py are illegal statements 19 Pointers and Arrays (cont’d) • When we pass an array name to a funcCon, we are passing the memory locaCon of the iniCal element (passing by reference) – Within the invoked funcCon, this argument is a local variable. A local variable containing an address. • By using this local variable (the address) we may manipulate the contents of the memory using indirecCon. • Because the address variable is local to the funcCon, it can be manipulated without aﬀecCng the memory 20 Pointers and Arrays (cont’d) • Example: /* charfind: return the position of an char in an array of char*/ int charfind(char *ptr, char c, int num) { int n; for (n=0;((*ptr != c)&amp;&amp;(n &lt; num)); ptr++) n++; return(n); } Since ptr is a pointer, we may increment it, and doing so will have no eﬀect on our array because we are only incremenCng our local copy of the pointer variable. 21 Pointers and Arrays (cont’d) • As a formal parameter in a funcCon deﬁniCon, char s; and char *s; are equivalent. However, when using an array the former is normally preferred because it explicitly indicates you are using an array. 22 Example of Pointer Use #include&lt;stdio.h&gt; void cubebyref(int *nptr); /*function prototype*/ int main() { int number = 5; /*initialize number...
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