Input and Output Revisited

1. Input and Output Revisited

2. Print the value of an integer variable Display Integer Variables – I Preprocessor: interact with input/output of your computer #include <stdio.h> int main() Start point of the program { } Start and finish of function int value1, value2, sum; Declare Variables value1 = 50; value2 = 30; Define Values sum = value1 + value2; Summation printf(“The sum of 50 and 30 is %i\n“, sum); Printing results return 0; Finish and return value 0 The sum of 50 and 30 is 80

3. Display Integer Variables – II #include <stdio.h> int main() { int value1, value2, sum; value1 = 50; value2 = 30; sum = value1 + value2; return 0; } printf(“The sum of %i and %i is %i\n“, value1, value2, sum); The sum of 50 and 30 is 80

4. int: integer Variables – Special Case I Starting with digit “0” • Octal notation. Base 8, not 10 • 0,1,2,3,4,5,6,7 0177 = 1*64 + 7*8 + 7 = 127 0256 = ? • Display • %i – print out the decimal value • %o – print out the octal value • %#o – print out the octal value, starting with 0

5. int: integer Variables – Special Case II Starting with digit “0x” • Hexadecimal notation. Based 16, not 10 • 0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F 0x177 = 1*256 + 7*16 + 7 = 375 0xAF = ? 0x2AF = ? • Display • %i – print out the decimal value • %x – print out the hexadecimal value • %#x – print out the hexadecimal value, starting with 0

6. float Variables - III • Display • %f – print out the decimal value • %e – print out the scientific notation • %g – let printf decide the format • -4 < value of exponent < 5: %f format • Otherwise: %e format

7. char: character Variables • For single character • Enclosing the character within a pair of ‘ ’ • ‘a’ • ‘;’ • ‘P’ • ‘\n’ • ‘1’ • One Byte • Display • %c

8. _Bool: Boolean Type • For boolean • 0/1 • Normally means false/true • 1 Byte long • Display • %i

9. Special variable types • short • usually use less space • add “h” after “%” in printf • long, long long • usually use more space • use “l” to indicate • add “l” after “%” in printf • signed, unsigned • specify whether is a signed quantity • use “u” to indicate unsigned • %u for unsigned

10. Summary of Data Type

11. Summary of Data Type – cont.

12. Getting Input • Need input from user • scanf • Same format as printf, except put “&” in front of variable names • scanf(“%i”, &count); • “&” means the "address of“ • to store whatever the user enters into the memory address where number is stored • Leaving out the & will cause your program to work incorrectly! • Exception: double uses %lf in scanf and %f in printf

13. Formatting Output • Sometimes you would like your output to have nice tabular output • Conversion specification (%i, %f, etc) allows for formatting text • Format : %[flags][width][.prec][hlL]type • [] mean its optional • Only % and type are mandatory

14. Flags

15. Width and Precision

16. hlL – Type Modifiers

17. Example 1 – Formatting Ints Integers: 425, 651, 1a9, 425 1a9, 1A9, 0x1a9, 0X1A9 +425, 425, 425, 425, 00425, 0000425 17, 21, 11, 17 61817, 170571, f179, 61817 75000, 222370, 124f8, 75000 1311768465173141112, 110642547402215053170, ... 1234567812345678, 1311768465173141112 #include <stdio.h> int main() { int i = 425; short int j = 17; unsigned int u = 0xf179U; long int l = 75000L; long long int L = 0x1234567812345678LL; printf("Integers:\n"); printf("%i, %o, %x, %u\n", i, i, i, i); printf("%x, %X, %#x, %#X\n", i, i, i, i); printf("%+i, %i, %5i, % 5i, %05i, %.7i\n", i, i, i, i, i, i); printf("%i, %o, %x, %u\n", j, j, j, j); printf("%i, %o, %x, %u\n", u, u, u, u); printf("%ld, %lo, %lx, %lu\n", l, l, l, l); printf("%lli, %llo, %llx, %llu\n", L, L, L, L); return 0; }

18. Example 2 – Formatting Floats Floats & Doubles: 12.978000, 1.297800e+01, 12.978 12.98, 1.30e+01 13, 1e+01 12.98, 1.30e+01 -97.458300, -9.745830e+01, -97.4583 -97.458 -97.46 -0097.46 #include <stdio.h> int main() { float f = 12.978F; double d = -97.4583; printf("Floats & Doubles:\n"); printf("%f, %e, %g\n", f, f, f); printf("%.2f, %.2e\n", f, f); printf("%.0f, %.0e\n", f, f); printf("%7.2f, %7.2e\n", f, f); printf("%f, %e, %g\n", d, d, d); printf("%.*f\n", 3, d); printf("%*.*f\n", 8, 2, d); printf("%0*.*f\n", 8, 2, d); return 0; }

19. Example 3 – Formatting Characters Characters: X X X 58 #include <stdio.h> int main() { char c = 'X'; printf("Characters:\n"); printf("%c\n", c); printf("%3c%3c\n", c, c); printf("%x\n", c); return 0; }

20. Example 4 – Formatting Strings #include <stdio.h> int main() { char s[] = "abcdefghijklmnopqrstuvwxyz"; printf("Strings:\n"); printf("%s\n", s); printf("%.5s\n", s); printf("%30s\n", s); printf("%20.5s\n", s); printf("%-20.5s\n", s); return 0; } Strings: abcdefghijklmnopqrstuvwxyz abcde abcdefghijklmnopqrstuvwxyz abcde abcde

21. More on scanf • Takes multiple modifiers between % and conversion specifier • Modifiers tell different things • Conversion specifiers are pretty much the same as printf with a few exceptions

22. scanf modifiers • * - field is to be skipped and not assigned • size – Maximum size of an input field • hh – stored in a signed or unsigned char • h – stored in a short int • l – value is to be stored in a long int • ll – value is to be stored in a long long int • L – value is to be stored in a long double

23. Conversion Characters - scanf

24. Conversion Characters - scanf

25. scanf characteristics • Skips leading whitespace except when reading with %c or bracket specifier […] • Stop reading a value • Field width is reached (if specified) • An invalid character for that field type is reached • Non formatting characters in scanf string are expected in input • scanf(“%i,%i,%i”, &i, &j, &k); - Expects 3 numbers separated by commas • White space characters match an arbitrary number of whitespace characters on the input • % in input is specifed by %%

26. scanf(“%i:%i:%i”, &h, &m, &s); • Reads three ints • Stored in integers h, m and s • Colons separate each • 23:34:52

27. scanf(“%i%%”, &percentage); • Reads one int • Stored in percentage • % symbol follows the int • 23%

28. Given input “29 w” • scanf(“%i%c”, &i, &c); • i  29 • c  ‘ ‘ • scanf(“%i %c”, &i, &c); • i  29 • c  ‘ w‘

29. Given input “144abcde 736.55 (wine and cheese)” • scanf(“%i %5c %*f %s”, &i, text, string); • i  144 • text[]  “abcde” • 736.55 Matched but skipped • string[] ”(wine” • scanf(“%s %s %i”, string2, string3, &i2); • string2 and • string3  cheese) • i2  waits for an integer input from user

30. More examples • scanf(“%80c”, text); • Waits for and reads next 80 characters and stores them in text • scanf(“%[^\n]\n”, buf); • Reads entire line into buf (excluding the new line character)

31. scanf - return • Returns the number of read AND assigned in the function call • scanf(“%i, %f, %i”, &i, &g, &j); • returns 3 on successful read and assignment • scanf(“%i, %*f, %i”, &i, &j); • returns 2 on successful read and assignment • Use for error checking if(scanf(“%i, %f, %i”, &i, &g, &j) != 3) { printf(“Error\n”); }