Notes for Tuesday 1 February

  • Meeting 5
  • read §4.1–4.2

Boolean expressions, logical operators, if, and else.

(We're one lecture behind, so above topics will be covered in Meeting 6.)

1 Assignment 2 solution 

#include <stdio.h>
int main1()
{
  float temp_f, temp_c;
  temp_f = 71.5;
  temp_c = (temp_f-32)/1.8f;
  printf("%f degrees Fahrenheit is"
         " %f degrees Celsius.\n",
         temp_f, temp_c);
  return 0;
}

2 Formatted Output

We learned about %f and %d format codes for printf. These are used to output floats and integers, respectively. But they have a few more features for formatted output. By default, for example, our float values were printing out with six digits after the decimal: 

printf("The answer is %f\n", 3.4);
// Result: The answer is 3.400000

2.1 Digits after decimal

It's possible to specify how many digits you want after the decimal point, just by modifying the format code. For example, %.2f will round off after two digits: 

printf("The answer is %.2f\n", 2.3491);
// Result: The answer is 2.35

2.2 Field width

2.3 More examples 

#include <stdio.h>
int ()
{
  printf("==%6.1f==\n", 358.26);
  printf("==%3.0f==\n\n", 15.9);
  printf("milk  %5.2f\n", 2.49);
  printf("bread %5.2f\n", 3.86);
  printf("candy %5.2f\n\n", 25.99);
  printf("Amount: %09.2f\n\n", 350.46);
  return 0;
}

3 Formatted Input 

#include <stdio.h>
int main()
{
  float temp_f, temp_c;

  printf("Enter temperature (F): ");
  scanf("%f", &temp_f);

  temp_c = (temp_f-32)/1.8f;
  printf("%.2f degrees Fahrenheit is"
         " %.0f degrees Celsius.\n",
         temp_f, temp_c);
  return 0;
}