newbie c++ help

[mikki2]

hi, i'm new to c++(just 3 days) and new to this forum too (so pls go easy on me). my problem is i can't remember how to use the for, while and do loops. but when i see a program with these loops in them i completely understand the program but can't write one cuz i keep forgeting how it's done. is there any "method" or "trick" you guys use to remember them? and if it's just that i need more practice can you link me to a site that has a bunch of "worked" examples and exercises?
thanks!

[Jessehk]

A for() loop is best used when you know (either based on a variable's value, or a set number) how many times a loop should run. For example, if I wanted to have a message printed exactly 5 times, I would do this:

for(int x = 0; x < 5; x++)
    std::cout << "Hello, world!" << std::endl;

A [I]while()[/I] loop is often used when you don't know how many times a loop should run, or are dependant on a changing condition to determined when you should exit the loop. For example:

#include <iostream>

int main() {
    std::string input("");
    
    while(input != "q") {
        std::cout << "\nEnter a message (\'q\' to quit):\n>>> ";
        std::getline(std::cin, input);
    }
}

A

do {
} while()

loop is used when you always want something to happen once, and then check a condition to see if it should happen again.

Hope what helped somewhat. :)

[msaqib]

Well within three days you can not understand all of the three loops :P.

It will take some time, all you can do is practice more and more and try to understand the code of others. This will help you alot while understanding the programming.

[mikki2]

thanks for the info..i havent checked my mail in a while thats why i'm just replying. and i have one more loop question...its a program to make a simple calculator. with this calculator presing "C" will clear the number and "Q" will exit the program. i've seen the way the book says it but i have changed a few things in it just for practice but it keeps saying "switch quantity not". i dont know what that means...any help?
anyway, here is the program pls show me where i have gone wrong. thanks

#include<iostream>
#include<stdlib.h>
using namespace std;
int main()
{
    double on_value = 0.0;
    double initial_value;
    double new_value;
    double second_value;
    double entry;
    double operand;
    double answer;
    cout<<on_value<<endl;
    
    cout<<"Input first entry: ";
    cin>>entry;
    new_value = on_value + entry;
    cout<<new_value<<endl;
    
    cout<<"Input operand: ";
    cin>>operand;
    
    switch (operand)
    {    
    case "C":
    cout<<on_value;
    break;
    
    case "+":
    cout<<"Input next number: ";
    cin>>entry;
    answer = new_value + entry;
    break;
    case "-":
    cout<<"Input next number: ";
    cin>>entry;
    answer = new_value - entry;
    break;
    case "/" :
    cout<<"Input next number: ";
    cin>>entry;
    answer = new_value / entry;
    break;
    case "*":
    cout<<"Input next number: ";
    cin>>entry;
    answer = new_value * entry;
    break;
    default:
    cout<<"Not understood. Inout proper operand"<<endl;
    }
    system("pause");
    return 0;
    }

p.s.
i have erased and put back a few things so i think it's a bit messy

[Dave Sinkula]

but i have changed a few things in it just for practice but it keeps saying "switch quantity not". i dont know what that means...any help?

double operand;
// ...
switch (operand)
{
   case "C":
   // ...

"switch quantity not an integer"? You can't use a switch with strings, either.

[mikki2]

thanks for the reply ...that was FAST!!! i changed the double operand to char operand and it worked fine thanks. oh yea i also changed the quotation (" ")marks found in the switch loop to apostrophe (' '). is there a way of knowing which is to be used?

[Dave Sinkula]

oh yea i also changed the quotation (" ")marks found in the switch loop to apostrophe (' '). is there a way of knowing which is to be used?

A single character enclosed within single-quotes is a character constant '@' .
A string of zero or more characters enclosed in double-quotes is a string literal: "string literal" .