C/C++ Syllabus

Strings

Strings are actually character arrays. The array points to the first character. String are terminated with a '\0'. String constants in a C program are enclosed in double quotes.

Some, but not all C++ implementations offera string class.

Declaring strings.

When declaring a string remember to include room for the `\0`. Strings may be initialized when declared as:

void declare()
{
  // Character arrays

  char a[20]="George Washington";
  char b[]  ="John Adams";

  cout << "1. a size = " << sizeof(a) << " = " << a << endl
       << "2. b size = " << sizeof(b) << " = " << b << endl;
          
  // String type

  string c = "Thomas Jefferson" ;

  cout << "3. c size = " << sizeof(c) << " = " << c << endl;

}
1. a size = 20 = George Washington
2. b size = 11 = John Adams
3. c size = 16 = Thomas Jefferson

Line Oriented input

To grab a line at a time use getline.

void line_input()
{
   char a[20];
   char b[20];
   char x;
   
   
   // Character arrays
   
   cout << " Please enter a string";
   cin >> a;
   cout << "4. " << a << endl;
   do { 
      cin.get(x);
   } while (x != '\n');   /// clear the line
   cout << " Please enter a string";
   cin.getline(b,20,'\n');
   cout << "5. " << b << endl;
   
   // string type 
   string c;
   
   cout << " Please enter a string";
   cin >> c;
   cout << "6. " << c << endl;
   do { 
      cin.get(x);
   } while (x != '\n');   /// clear the line
   cout << " Please enter a string ";
   getline(cin,c );
}
 Please enter a string James Madison
4. James
 Please enter a string James Madison
5.  James Madison
 Please enter a stringJames Monroe
6. James
 Please enter a string James Monroe
7. James Monroe

String functions.

Because strings are used in many programming applications there is a C library of common string functions. Note all string functions assumed the string is terminated with '\0'. To use these functions the header file <string>

void copycat()
{
// Character arrays;
   
   int a;
   char b[30]="John Q. Adams";
   a=strlen(b);
   cout <<"8. " <<  b << "size = " << sizeof(b) 
        << " length = " << strlen(b) << endl;
   
   char c[30]="Andrew Jackson";
   strcpy(b,c);
   cout << "9. " <<  b << endl;
   
   char d[30]="";
   strncpy(d,c,6);
   cout << "10. " <<  d << endl;
     
   char e[30]="Martin ";
   strcat(e,"Van Buren");
   cout << "11. " <<  e << endl;
   
   char f[30];
   strcat(strcpy(f,"William")," Henry Harrison");
   cout << "12. " << f << endl;
   
   // string types;
   
   string g;
   g="John Tyler";
   cout << "13. " << g << endl;
   
   string h="James ";
   h = h + "Polk";
   cout << "14. " << h <<endl;

}
8. John Q. Adamssize = 30 length = 13
9. Andrew Jackson
10. Andrew
11. Martin Van Buren
12. William Henry Harrison
13. John Tyler
14. James Polk

void compare()
{
   // Character arrays;
   
   char i[30]="Zachry Taylor";
   char j[30]="Abraham Lincoln";
    
   if(strcmp(i,j)!=0) {
      cout <"15. " << i << " Is no " << j <<endl;
   }
   if(strncmp(i,"Zach",4) == 0){
      cout <g< "16. but is a Zach" <<endl;
   }
   
   // string types
   string k = "Millard Fillmore";
   string l = "Abraham Lincoln";
   
   if(k != l ) {
      cout <g< "17. " << k << " is no " << l << endl;
   }
   if( k.substr(0,7) == "Millard") {
      cout <g<"18.  but is a  Millard" << endl;
   }
}
15. Zachry Taylor Is no Abraham Lincoln
16. but is a Zach
17. Millard Fillmore is no Abraham Lincoln
18.  but is a  Millard

void reverse()
   {
   
   // character arrays
   
   char m[30]="Franklin Pierce";
   char *p;   
   cout << "19. " << m << endl;
   p=strchr(m,' ');
   *p='\0';
   p++;
   cout << "20. " << p << ", " << m << endl;
   
   // string types
   
   string n ="James Buchanan";
   int here;
   string::size_type there;
   cout << "20. " << n << endl;
   here = n.find(' ');
   there = n.length();
   cout << "21. " << n.substr(here+1,there) << ", " << n.substr(0,here) << endl;

}
19. Franklin Pierce
20. Pierce, Franklin
20. James Buchanan
21. Buchanan, James

example

coneverting binary and decimal

/*
 reads in numbers as strings
 binary number preceeded with 0 (zero)
 converts to other base. handles base ten and 2.

  BLUE code uses string types, Gray code (not blue) uses
  character arrays
*/

#ifdef BLUE
  #include <string> 
#else
  #include <string.h>
#endif

#include <iostream>
using namespace std;



#ifdef BLUE
  int  input(string,int);   // Protoype for using string
#else
  int  input(char*,int);     // prototype for using char*
#endif

void print(int,int);

void main()
{

#ifdef BLUE
   string s1;
#else
   char s1[20];
#endif

  int inbase,outbase,number;

#ifdef BLUE
   cout << " Running BLUE code " << endl;
#else
   cout << " Running Gray code " << endl;
#endif

   do {
      cout << " Enter the number, q to quit :";
      cin >> s1;
      if(s1[0] == 'q' ) break;
      if(s1[0] == '0' ) {
           inbase =2;
           outbase=10;
      } else {
           inbase=10;
           outbase=2;
      }
      number=input(s1,inbase);
      print(number,outbase);
      cout << endl;
   } while (1);
}
#ifdef BLUE
int input(string s1, int inbase)
{
   string::size_type len;
   int  i, value =0;

   len=s1.length();
   for(i=0;i<len;i++)
      value=value*inbase + s1[i] -'0';
   return value;
}
#else
int input(char *s1,int inbase)
{
   int value=0;
   while(*s1) {
      value=value * inbase + *s1 - '0';
      s1++;
   }
   return value;
}
#endif
void print(int number, int outbase)
{
   int q,r;

   q=number/outbase;
   r=number%outbase;
   if(q) {
      print(q,outbase);
   }
   cout << r;
}

 Running Gray code
 Enter the number, q to quit :010101
21
 Enter the number, q to quit :21
10101
 Enter the number, q to quit :q
Press any key to continue

Then add 
#define BLUE to code;
recompile and rerun:

 Running BLUE code
 Enter the number, q to quit :011011011
219
 Enter the number, q to quit :219
11011011
 Enter the number, q to quit :q
Press any key to continue