1. EECE.2160 ECE Application Programming
Instructor:
Dr. Michael Geiger
Fall 2018
Lecture 5:
Basic variable output with printf()
Basic variable input with scanf()

2. ECE Application Programming: Lecture 5
Lecture outline
Announcements/reminders
Program 2 due Friday, 9/21
Review
Operators
Basic variable output with printf()
Today’s lecture
printf() examples
scanf()
6/5/2019
ECE Application Programming: Lecture 5

3. Review: Arithmetic Operations
Operator
Addition +
Subtraction -
Multiplication *
Division /
Modulus Division
(Remainder) %
6/5/2019
ECE Application Programming: Lecture 5

4. Review: printf() basics
To print variables (or constants), insert %<type> in your printf() format string
%c: single character
%d or %i: signed decimal integer
%f: float; %lf: double
Prints 6 digits after decimal point by default
To control # digits, use precision
"%.4lf" prints with 4 digits (4th digit rounds)
"%.0lf" prints with 0 digits (round to nearest integer)
Each %<type> must correspond to a variable or constant that follows
printf("a=%.3f, b=%.2f", a, b);
6/5/2019
ECE Application Programming: Lecture 6

5. ECE Application Programming: Lecture 5
printf() example
float a=67.49,b= ; printf("hello %f there %f\n",a,b); printf("%f%f%f%f\n",a,a,b,b); printf("a=%.2f, b=%.1f",a,b); printf("Cool huh?\n");
Printed:
hello there a=67.49, b=10.0Cool huh?
6/5/2019
ECE Application Programming: Lecture 5

6. ECE Application Programming: Lecture 5
printf() details
Detailed slides on printf() follow
Skip these if you don’t want to go overboard with the full details of how the function works
6/5/2019
ECE Application Programming: Lecture 5

7. ECE Application Programming: Lecture 5
02/07/2005
printf()
Documentation info:
int printf(const char *format [,argument] ...)
Type of value returned
Name of function
( ) indicate printf is a function
First arg type and formal name (required, since no brackets)
next argument type and name (in this case it may be any simple type)
[ ] indicate optional arguments
… indicates previous argument repeated zero or more times
6/5/2019
ECE Application Programming: Lecture 5
(c) 2005, P. H. Viall

8. ECE Application Programming: Lecture 5
printf()
int printf(const char *format [,argument] ...)
Type of value returned (int in this case)
All functions return at most one value.
The type void is used to indicate a function returns no value
There is no requirement to use the value returned.
The printf() function returns the number of characters printed (including spaces); returns negative value if error occurs.
6/5/2019
ECE Application Programming: Lecture 5

9. ECE Application Programming: Lecture 5
printf()
int printf(const char *format [,argument] ...)
Name of function; printf( ) in this case
A function name is ALWAYS followed by a set of (), even if the function takes no arguments
6/5/2019
ECE Application Programming: Lecture 5

10. ECE Application Programming: Lecture 5
printf()
int printf(const char *format [,argument] ...)
Type (const char *) and name (format) of first argument
For the moment, const char * can be thought of as a series of characters enclosed in double quotes
The name format may be thought of as a code indicating how the arguments are to be interpreted, and how the output should look.
6/5/2019
ECE Application Programming: Lecture 5

11. ECE Application Programming: Lecture 5
printf()
int printf(const char *format [,argument] ...)
zero of more optional arguments, each preceded by a comma
zero because of the …
optional because of the [ ]
6/5/2019
ECE Application Programming: Lecture 5

12. ECE Application Programming: Lecture 5
Example: printf()
Show the output from each programs(assume #include <stdio.h> for all)
void main() {
int i=2, j=3, k, m;
k = j * i;
m = i + j;
printf("%d %d %d %d\n", i, j, k, m); }
double f, g;
f = 1.0 / 4.0;
g = f * 20;
printf("f = %lf,\ng = %.2lf\n", f, g);
int a = 5, b = 2;
printf("Output%doesn't%dmake%dsense", a, b, a + b);
6/5/2019
ECE Application Programming: Lecture 5

13. ECE Application Programming: Lecture 5
Example solution
void main() { int i=2, j=3, k, m; k = j * i; k = 2 * 3 = 6 m = i + j; m = = 5 printf("%d %d %d %d\n", i, j, k, m); } Output:
6/5/2019
ECE Application Programming: Lecture 5

14. Example solution (cont.)
void main() { double f, g; f = 1.0 / 4.0; f = 0.25 g = f * 20; g = 0.25 * 20 = 5 printf("f = %lf,\ng = %.2lf\n", f, g); } Output: f = , g = 5.00 (remember, 6 places after decimal point printed by default with floating-point data)
6/5/2019
ECE Application Programming: Lecture 5

15. Example solution (cont.)
void main() {
int a = 5, b = 2;
printf("Output%doesn't%dmake%dsense",
a, b, a + b); }
Output: Output5oesn't2make7sense
(Every %d gets replaced with a number, which is underlined above to show what happens—in practice, the console isn’t going to underline your output!)
6/5/2019
ECE Application Programming: Lecture 5

16. ECE 160 - Introduction to Computer Engineering I
02/09/2005
scanf() function
Used to get input from user
Returns number of items successfully assigned
First argument is format specifiers
Essentially same as printf() format string
Every format specifier (%d, %lf, etc.) corresponds to an input value to be read
Format string can contain other characters, which will be ignored if they are present
If they’re not, you have a problem …
Remaining arguments are variable addresses
Use “address of” operator: &
For example, given: int a;
 The address of a is: &a
6/5/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

17. ECE Application Programming: Lecture 6
scanf() and scanf_s()
Visual Studio users will see an error message when using scanf()
Function is technically not secure (not that it matters for our purposes)
Suggests use of scanf_s()
Windows-specific “secure” scan function
Preferred method of removing warnings:
#define _CRT_SECURE_NO_WARNINGS
That line must come before
#include <stdio.h>
6/5/2019
ECE Application Programming: Lecture 6

18. ECE 160 - Introduction to Computer Engineering I
02/09/2005
scanf() function
Documentation info:
int scanf(const char *format [,argument] ...)
format - is format specifiers similar to printf() specifiers
arguments - are ADDRESSES of where to store what the user enters
6/5/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

19. ECE 160 - Introduction to Computer Engineering I
02/09/2005
scanf() function
int hours; float rate;
scanf("%d %f",&hours,&rate);
If user types:
34 5.7
hours ?
1284
rate ?
1288
hours 34
1284
rate
5.7
1288
6/5/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

20. scanf() format strings
scanf() will skip space characters for all types but %c
Read input until it finds something that’s not a space, then see if it matches the desired type
If type matches, value will be stored in specified variable
If type doesn’t match, nothing stored; function stops
Space in string only matters if using %c
%c will read any character
Includes spaces, newlines, etc.
Example: given scanf("%d%c", &i, &c);
Input: 3a  i = 3, c = 'a'
Input: 3 a  i = 3, c = ' '
Input: 3
a  i = 3, c = '\n' (assuming newline directly after 3)
6/5/2019
ECE Application Programming: Lecture 6

21. ECE Application Programming: Lecture 6
scanf() return value
scanf() returns # of successfully read items
Ex.: given scanf("%d%d", &x, &y);
Input: 3 7  x = 3, y = 7, return value = 2
Input:  x = 3, y = 7, return value = 2
Input:  x = 3, y = ?, return value = 1
y is unchanged
Input: x1 7  x = ?, y = ?, return value = 0
x, y both unchanged
Can assign return value to variable
Example:
int numRead; // # input values read
numRead = scanf("%d%d", &x, &y);
6/5/2019
ECE Application Programming: Lecture 6

22. ECE Application Programming: Lecture 6
Example
Variables: int i; double d; char c;
What values are read for each of the following inputs and scanf() calls? Assume the input is as follows:
scanf("%d%lf", &i, &d)
scanf("%d %lf", &i, &d)
scanf("%lf%d", &d, &i)
scanf("%d%c", &i, &c)
scanf("%d %c", &i, &c)
6/5/2019
ECE Application Programming: Lecture 6

23. ECE Application Programming: Lecture 6
Example solution
What values are read for each of the following inputs and scanf() calls?
scanf("%d%lf", &i, &d)
 i = 34, d = 5.7
scanf("%d %lf", &i, &d)
scanf("%lf%d", &d, &i)
 d = 34, i = 5
scanf("%d%c", &i, &c)
 i = 34, c = ' ' (space)
scanf("%d %c", &i, &c)
 i = 34, c = '5'
6/5/2019
ECE Application Programming: Lecture 6

24. Using scanf() and printf() together
ECE Introduction to Computer Engineering I
02/09/2005
Using scanf() and printf() together
#include <stdio.h>
int main() { int hours; float rate; float grosspay; printf("Enter hours: "); scanf("%d",&hours); printf("Enter pay rate: "); scanf("%f",&rate); grosspay = hours * rate; printf("You earned $%f\n",grosspay); }
6/5/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

25. scanf() function - Payroll Ver 2
ECE Introduction to Computer Engineering I
02/09/2005
scanf() function - Payroll Ver 2
#include <stdio.h>
int main() { double hours; double rate; double grosspay; printf("Enter hours: "); scanf("%lf",&hours); printf("Enter pay rate: "); scanf("%lf",&rate); grosspay = hours * rate; printf("You earned $%lf\n",grosspay); }
6/5/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

26. ECE Application Programming: Lecture 5
Final notes
Next time
PE1: Flowcharts and debugging
Reminders:
Program 2 due Friday, 9/21
6/5/2019
ECE Application Programming: Lecture 5