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Pointers and Arrays

Started by SubImpact Aug 22, 2006 at 5:19 PM 3 replies 1k views

Original Post

Aug 22, 2006 at 5:19 PM

Im doing a part in my C++ book about pointers and arrays and this is the example from the book. When I compile and run it it only shows Array of integers 98 at 2359120 -486 at 2359124 301589 at 2359128 Array of chars: Array of doubles: ------------------------------------------------------- Here is the code, what is wrong with it?

[source lang ="cpp"]
#include <iostream>

int main(){
    const unsigned short ITEMS = 3;
    
    int intArray[ITEMS] = {98,-486,301589};
    char charArray[ITEMS] = {'A','B','C'};
    double doubleArray[ITEMS] = {3.14315614, 2.74546944, 7.349e14};
    
    int *intPtr = intArray;
    char *charPtr = charArray;
    double *doublePtr = doubleArray;
    
    std::cout<<"Array of integers:\n";
    
    for (int i; i < ITEMS; ++i){
        std::cout<< *intPtr <<" at "<< reinterpret_cast<unsigned long>(intPtr)<<"\n";
        intPtr++;
        }
        
    std::cout<<"\nArray of chars:\n";
    
    for (int i; i< ITEMS; ++i){
        std::cout<< *charPtr <<" at "<< reinterpret_cast<unsigned long>(charPtr)<<"\n";
        charPtr++;
        }
        
    std::cout<<"\nArray of doubles:\n";
    
     for (int i; i< ITEMS; ++i){
        std::cout<< *doublePtr <<" at "<< reinterpret_cast<unsigned long>(doublePtr)<<"\n";
        doublePtr++;
        }
     
     std::cin.get();
     return 0;
}

ToohrVyk

238

ToohrVyk

Aug 22, 2006 at 5:21 PM

Initialize i.

Sam Gamgee

Aug 22, 2006 at 5:26 PM

Yup, as the above poster said, those 'for' statements should be something like so:

for (int i=0; i < ITEMS; ++i){

SubImpact

Author

SubImpact

Aug 22, 2006 at 6:56 PM

Woops, dumb mistake, I messed up on the first for loop and just copyed it and pasted and change the vars. Thanks.

Zahlman

257

Zahlman

Aug 23, 2006 at 2:33 AM

Quote:
Original post by SubImpact
Woops, dumb mistake, I messed up on the first for loop

That's why you don't write for loops when there are standard library algorithms that deal with your situation, or at least iterate using iterators instead of a count variable if possible.

Quote:
and just copyed it and pasted and change the vars. Thanks.

That's why you (much more importantly than above) don't copy-and-paste things, but instead make helper functions.

#include <iostream>#include <algorithm>template <typename T>// Have to pass by reference here, so that '&value' yields the address of the// original rather than a copy.void report(const T& value) {  std::cout << value << " at "             << reinterpret_cast<unsigned long>(&value) << "\n";}template <typename T>void reportArray(T* begin, T* end, const char* type_label) {  std::cout << "Array of " << type_label << "s:\n";  std::for_each(begin, end, report<T>);  std::cout << std::endl;}int main(){    const unsigned short ITEMS = 3;        int intArray[ITEMS] = {98,-486,301589};    reportArray(intArray, intArray + ITEMS, "integer");    char charArray[ITEMS] = {'A','B','C'};    reportArray(charArray, charArray + ITEMS, "char");    double doubleArray[ITEMS] = {3.14315614, 2.74546944, 7.349e14};    reportArray(doubleArray, doubleArray + ITEMS, "double");}

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