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@derekmma
Created Oct 8, 2021
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Demo program for Week 2, CS31 Fall 2021 Discussion 1C
/* Demo program for CS31 Discussion 1C Week 2
Oct 8, 2021, Mingyu Derek Ma
*/
#include <string>
#include <iostream>
using namespace std;
void example1(){
/*
Example 1: cin only takes numeric part
*/
// cin only takes numeric part
int num1, num2;
cin >> num1;
cout << num1 << endl;
// if input is " 12 ", the num is 12
cin >> num2;
cout << num2 << endl;
// if input is " 12 34 567 ", the num is 12
}
void example2(){
/*
Example 2: use getline() to get string input
*/
// 1- Use getline() to get string input
cout << "Input a string: ";
string stringInput;
getline(cin, stringInput); // reads whole line (with spaces) into a string variable
// cin >> stringInput; // WRONG - doesn't read spaces
cout << "The string input is " << stringInput << endl;
}
void example3(){
/*
Example: use getline() right after cin
*/
// Wrong version
string stringInput = "";
cout << "Input a double: "; // example input: 2.5, ' 11 22 33'
double x;
cin >> x;
cout << "Input a string: ";
getline(cin, stringInput); // only takes newline and stop
cout << x << endl;
cout << stringInput << endl;
// Right version
stringInput = "";
cout << "Input a double: ";
cin >> x;
cin.ignore(10000, '\n'); // add this line!
cout << "Input a string: ";
getline(cin, stringInput);
cout << x << endl;
cout << stringInput << endl;
}
void example4(){
/*
Example: arithmetic operators
*/
int x;
x = 11 * 2 + 3;
cout << x << endl;
x = 3 + 11 * 2;
cout << x << endl;
x = 11 * (2 + 3);
cout << x << endl;
// Data types in arithmetic operation
int a;
double b;
a = 10/4;
b = 10/4;
cout << a << endl;
cout << b << endl;
}
void example5(){
/*
Example: component assignment and
incremental operators
*/
int i = 5;
i += 200;
cout << i << endl;
i -= 200;
cout << i << endl;
i *= 100;
cout << i << endl;
i /= 20;
cout << i << endl;
i %= 20;
cout << i << endl;
i++;
cout << i << endl;
i--;
cout << i << endl;
int j;
j = ++i;
cout << i << ' ' << j << endl; // 6 6
j = i++;
cout << i << ' ' << j << endl; // 7 6
int a=5, b, c;
b = ++a; // a is 6, b is also 6
cout << "a is " << a << ", b is " << b << ", c is " << c << endl;
c = b++; // c is 6, b becomes 7
cout << "a is " << a << ", b is " << b << ", c is " << c << endl;
}
void example6(){
/*
Example: If else statements
*/
int a = 61;
int gold_criteria = 80;
if(a < gold_criteria)
cout << "a does not get gold award." << endl;
else
cout << "Congratulations! a get gold award!" << endl;
cout << "--------" << endl;
// Wrong version: lead to compile error
// if(a != criteria)
// cout << "a does not meet criteria." << endl;
// cout << "Work harder" << endl;
// else
// cout << "Congratulations!" << endl;
// Right version
if(a < gold_criteria){
cout << "a does not get gold award." << endl;
cout << "Work harder" << endl;
} else
cout << "Congratulations! a get gold award!" << endl;
cout << "--------" << endl;
// Define variables inside block
if(a < gold_criteria){
cout << "a does not get gold award." << endl;
int silver_criteria = 60;
if(a >= silver_criteria)
cout << "You get silver award!" << endl;
} else
cout << "Congratulations!" << endl;
// Compile error: silver_criteria is not defined.
// cout << "Criteria for silver award is " << silver_criteria << " score.";
}
void example7(){
/*
Example: Scopes in if else statements, especially
when there is only if statements
*/
int a = 61;
int gold_criteria = 80;
int silver_criteria = 60;
// Wrong version
if(a > silver_criteria)
if(a > gold_criteria)
cout << "Congratulations! a get gold award!" << endl;
else // this else condition correspond to a > gold_criteria condition
cout << "Sorry, a does not get any award." << endl;
// Right version 1
cout << "--------" << endl;
if(a > silver_criteria)
{
if(a > gold_criteria)
cout << "Congratulations! a get gold award!" << endl;
}
else // this else condition correspond to a > silver_criteria condition
cout << "Sorry, a does not get any award." << endl;
// Right version 2
cout << "--------" << endl;
if(a > silver_criteria)
if(a > gold_criteria)
cout << "Congratulations! a get gold award!" << endl;
else ;
else // this else condition correspond to a > silver_criteria condition
cout << "Sorry, a does not get any award." << endl;
}
void example8(){
/*
Example: else if
*/
int a = 61;
int gold_criteria = 80;
int silver_criteria = 60;
int bronze_criteria = 40;
if(a > gold_criteria)
cout << "Congratulations! a get the gold award!" << endl;
else if(a > silver_criteria)
cout << "Congratulations! a get the silver award!" << endl;
else if(a > bronze_criteria)
cout << "Congratulations! a get the bronze award!" << endl;
else
cout << "Sorry, a does not get any award." << endl;
}
void example9(){
/*
Example: Take care of the boolean expression
many other things can return boolean value
*/
// If the condition is integer 0, then it's treated as False if you need a T/F value
// If the condition is non-zero integer, then it's treated as True if you need a T/F value
if (1)
cout << "We are in the True branch of the if statement" << endl;
else
cout << "We are in the False branch of the if statement" << endl;
if (0)
cout << "We are in the True branch of the if statement" << endl;
else
cout << "We are in the False branch of the if statement" << endl;
if (5)
cout << "We are in the True branch of the if statement" << endl;
else
cout << "We are in the False branch of the if statement" << endl;
int a = 666;
// Assignment statement means evaluate expression, then put result in variable and produce new value of variable. So a=333 when produce 333 if it's a condition
if (a = 333)
cout << "We are in the True branch of the if statement" << endl;
else
cout << "We are in the False branch of the if statement" << endl;
if (a = 0)
cout << "We are in the True branch of the if statement" << endl;
else
cout << "We are in the False branch of the if statement" << endl;
if ("hello world")
cout << "We are in the True branch of the if statement" << endl;
else
cout << "We are in the False branch of the if statement" << endl;
}
void example10(){
/*
Another example of setting scope for if statements
*/
int a = 4, b = 4;
if (a == 4)
if (a == b)
a++;
if (a != b)
a++;
cout << a << endl; // a is 6, b is 4
a = 4;
if (a == 4) {
if (a == b)
a++;
}
if (a != b)
a++;
cout << a << endl;
a = 4;
if (a == 4) {
if (a == b)
a++;
if (a != b)
a++;
}
cout << a << endl;
}
int main(){
example1();
// example2();
// example3();
// example4();
// example5();
// example6();
// example7();
// example8();
// example9();
}
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