Commonly Asked C/C++ Questions

#include <iostream>
#include <string>

using namespace std;

int main()
{
    string name;
    cout<<"Enter a name:\n";
    getline(cin, name);
    cout<<name<<endl;

    return 0;
}

#include <stdlib.h>
int main(void)
{
     char *buf1 = "42";
     char buf2[] = "69.00";
     int i;
     double d;
     long l;
     i = atoi(buf1);
     l = atol(buf1);
     d = atof(buf2);
     return 0;
}

#include <stdio.h>
int main(void)
{
    int i = 42;
    float f = 69.0;
    double d = 105.24;
    long l = 23;
    char buf[50];
 
    sprintf(buf, "%d", i);
    sprintf(buf, "%f", f);
    sprintf(buf, "%f", d);
    sprintf(buf, "%ld", l);
    sprintf(buf, "%d %f %ld", i, f, l);
    return 0;
}    

#include <sstream>
#include <string>
using namespace std;

int main(void) {
    stringstream ss;
    int i = 42;
    double d = 105.24;

    ss << i << " " << d;

    // Convert to string or char array
    string s = ss.str();
    char buf[50];
    sprintf(buf, ss.str().c_str());
}

#include <stdlib.h>
#include <stdio.h>
int main(void)
{
  long l; int i;
  unsigned int ui;
  char *hexstr = "12FC3";
  char *octstr = "1245";
  char *binarystr = "1101";

  l = strtol(hexstr, NULL, 16);
  l = strtol(octstr, NULL, 8);
  l = strtol(binarystr, NULL, 2);
  sscanf("12", "%d", &i);
  sscanf("14", "%ld", &l);
  sscanf(hexstr, "%x", &ui);
  sscanf(hexstr, "%o", &ui);

  return 0;
}

#include <sstream>
#include <string>
using namespace std;

int main(void)
{
  long l; int i;
  char *hexstr = "12FC3";
  char *octstr = "1245";
  stringstream ss;

  ss << hex << hexstr;
  ss >> l;
  ss.clear();
  ss << oct << octstr;
  ss >> i;

  return 0;
}

#include <stdio.h>
int main(void)
{
    int i = 42;
    char buf[50];
    sprintf(buf, "%x", i); /* convert to hex */
    sprintf(buf, "%o", i); /* convert to octal */
    return 0;
}

#include <sstream>
#include <string>
using namespace std;

int main(void)
{
  int i = 42;
  char buf[50];
  stringstream ss;
  ss << hex << i;
  ss >> buf;

  ss.clear();
  ss << oct << i;
  ss >> buf;
  return 0;
}

char ch;
int i;

ch = 'A';
i = ch; /* Assigns the ASCII value of 'A' (i.e.) 65 to i */
printf("%d\n", i); /* Prints 65 */

int i;
char ch;

i = 65;
ch = (char) i;
/* some compilers don't warn you if you do:
ch = i;
and some will, hence the explicit cast to char type. The cast
assures the compilers that warn you, that you know what you're doing. */
printf("%c\n", ch); /* prints 'A' */

char ConvertToUpperCase(char ch) {
   if (ch >= 'a' && ch <= 'z')
      ch = ch - 'a' + 'A';
   return ch;
}

#include <stdio.h>

int main(void)
{
  int i = 23; long l = 42;
  float f = 105.23; double d = 69.05;
  long double ld = 55.23; long long ll = 92;
  char c='a'; char s[] = "This is a string";

  printf("int = %d\nlong = %ld\n", i, l);
  printf("float = %f\ndouble = %fd\n", f, d);
  printf("long double = %Lf\nlong long = %lld\n", ld, ll);
  printf("char = "%c\nString=%s\n", c, s);

  return 0;
}

#include <stdio.h>

int main(void)
{
  float f = 105.2345;
  char buf[] = "This is a string";

  /* Limit to 2 decimals */
  printf("float = %.2f\n", f);
  /* Print 10 chars wide, limit to 2 decimals */
  printf("float = %10.2f\n", f);
  /* Print 10 chars wide, limit to 2 decimals and left-justify */
  printf("float = %-10.2f\n", f);
  /* Limit to 10 characters */
  printf("%.10s\n", buf);

  return 0;
}

#include <iostream>
#include <iomanip>
using namespace std;

int main(void)
{
  float f = 105.2345;
  char buf[] = "This is a string";

  cout.setf(ios::fixed);
  /* Limit to 2 decimals */
  cout << setprecision(2) << f << endl; 
  /* Print 10 chars wide, limit to 2 decimals */
  cout << setw(10) << setprecision(2) << f << endl; 
  /* Right justify to 30 chars */
  cout << setw(30) << buf << endl; 

  return 0;
}

char buf[25];
scanf("%20s", buf);

cin >> setw(20) >> buf;
cin.get(buf, 20);