1. EECE.2160 ECE Application Programming
Instructors:
Dr. Michael Geiger & Dr. Lin Li
Spring 2019
Lecture 5:
Basic variable output with printf()
Basic variable input with scanf()

2. ECE Application Programming: Lecture 5
Lecture outline
Announcements/reminders
Textbook exercises due 3 days after each lecture
Program 2 due Monday, 2/11
Today’s lecture
Program 2 overview
Review: operators, printf() basics
printf() examples
scanf()
4/23/2019
ECE Application Programming: Lecture 5

3. ECE Application Programming: Lecture 5
Program 2 overview
Learn basic I/O
Basic circuit analysis
All formulas on last page of figures document
zyBooks-specific note
Must write all input for program ahead of time
Visual Studio-specific note
To avoid scanf() warnings, include following line before #include <stdio.h>:
#define _CRT_SECURE_NO_WARNINGS
4/23/2019
ECE Application Programming: Lecture 5

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

5. 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);
4/23/2019
ECE Application Programming: Lecture 6

6. 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?
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ECE Application Programming: Lecture 5

7. 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);
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ECE Application Programming: Lecture 5

8. 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:
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ECE Application Programming: Lecture 5

9. 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)
4/23/2019
ECE Application Programming: Lecture 5

10. 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!)
4/23/2019
ECE Application Programming: Lecture 5

11. 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
4/23/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

12. 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>
4/23/2019
ECE Application Programming: Lecture 6

13. 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
4/23/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

14. 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
4/23/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

15. 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)
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ECE Application Programming: Lecture 6

16. 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);
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ECE Application Programming: Lecture 6

17. 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)
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ECE Application Programming: Lecture 6

18. 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'
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ECE Application Programming: Lecture 6

19. 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); }
4/23/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

20. 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); }
4/23/2019
ECE Application Programming: Lecture 6
(c) 2005, P. H. Viall

21. ECE Application Programming: Lecture 5
Final notes
Next time
Finish scanf() introduction
PE1: Flowcharts and debugging
Reminders:
Textbook exercises due 3 days after each lecture
Program 2 due Monday, 2/11
4/23/2019
ECE Application Programming: Lecture 5