1. 16.216 ECE Application Programming Instructor: Dr. Michael Geiger Spring 2013 Lecture 6: printf() formatting

2. Lecture outline Announcements/reminders  Program 2 due Wednesday, 2/6  Program 3 to be posted; due 2/13 Today’s class  printf() formatting  Operators 5/15/2015 ECE Application Programming: Lecture 6 2

3. Formatted output: field width Specifying field width (min # characters) (assume n = 12):  printf(“%10d”, n);  12 (8 spaces, then number 12) To left justify value in field, use – flag before width  printf(“%-10d”, n);  12________ (Number 12, then 8 spaces) To force the sign to show, use + flag before width  printf(“%+10d”, n);  +12 (7 spaces, a plus sign, then number 12) To place 0s before the value, use 0 flag before width  printf(“%010d”, n);  0000000012  printf(“%+010d”, n);  +000000012  printf(“%-010d”, n);  12________ To use a variable to specify field width, use * as the width  printf(“%*d”, n, n);  12 (Field width = 12  10 spaces, then the number 12) Field width never truncates  printf(“%1d”, n);  still prints 12 5/15/2015 ECE Application Programming: Lecture 4 3

4. Formatted output: precision For examples, int n = 12; double x = 3.754 Specifying precision:  # chars after decimal point for FP (%f, %lf) Rounds last digit printf(“%.6lf”, x);  3.754000 printf(“%.1lf”, x);  3.8 printf(“%.0lf”, x);  4  Minimum # chars for integer (%d, %i, %u, %x) Does not truncate; will pad with leading 0s printf(“%.1d”, n);  12 printf(“%.3d”, n);  012  Max # chars for string (%s) printf(“%.5s”, “one”);  one printf(“%.5s”, “one two”);  one t  No effect for char (%c) As with field width, can use * to specify that field width is a variable 5/15/2015 ECE Application Programming: Lecture 4 4

5. Formatting and scanf() Formatting specified above used only for printf() Have very different meaning for scanf()  printf("%3d", x)  print x w/field width of 3  scanf("%3d", &x)  read 3 characters into x If you enter: 12  x = 12 If you enter: 1234  x = 123 Bottom line: you probably don’t want to “format” your input! 5/15/2015 ECE Application Programming: Lecture 4 5

6. Note The next three slides contain full specification for printf() flags, field width, and precision Read on if you want lots of details; skip these slides if the previous ones were sufficient 5/15/2015 ECE Application Programming: Lecture 4 6

7. 7 printf format specifications General form:% [flags] [width] [.precision] [ { h | l | I64 | L } ] type flagmeaningdefault -Left align the result within the given field widthRight align +Prefix the output value with a sign (+ or -) if the output value is of a signed type. Sign appears only for negative signed values (-) 0If width is prefixed with 0, zeros are added until the minimum width is reached. If 0 and - appear, the 0 is ignored. No padding (actually space padding) blankPrefix the output value with a blank if the output value is signed and positive; the blank is ignored if both the blank and + flags appear. No blank appears #When used with the o, x, or X format, the # flag prefixes any nonzero output with 0, 0x, or 0X, respectively. Ignored when used with c, d, i, u, or s. No prefix #When used with the e, E, or f format, the # flag forces the output value to contain a decimal point in all cases. Decimal point appears only if digits follow it. #When used with g or G format, forces the output value to contain a decimal point in all cases and prevents the truncation of trailing zeros. Decimal point appears only if digits follow it. Trailing zeros are truncated. This slide adapted from information in MSDN Library 5/15/2015 ECE Application Programming: Lecture 4

8. 8 printf format specifications General form:% [flags] [width] [.precision] [ { h | l | I64 | L } ] type The width argument is a nonnegative decimal integer controlling the minimum number of characters printed. If the number of characters in the output value is less than the specified width, blanks are added to the left or the right of the values — depending on whether the – flag (for left alignment) is specified — until the minimum width is reached. Notes: If width is prefixed with 0, zeros are added until the minimum width is reached (not useful for left-aligned numbers). The width specification never causes a value to be truncated. If the number of characters in the output value is greater than the specified width, or if width is not given, all characters of the value are printed (subject to the precision specification). This slide adapted from information in MSDN Library 5/15/2015 ECE Application Programming: Lecture 4

9. 9 printf format specifications General form:% [flags] [width] [.precision] [ { h | l | I64 | L } ] type typmeaningdefault cThe precision has no effectcharacter is printed d,i, u,o, x,X The precision specifies the minimum number of digits to be printed. If the number of digits in the argument is less than precision, the output value is padded on the left with zeros. The value is not truncated when the number of digits exceeds precision Default precision is 1. e,EThe precision specifies the number of digits to be printed after the decimal point. The last printed digit is rounded. Default precision is 6; if precision is 0 or the period fThe precision value specifies the number of digits after the decimal point. If a decimal point appears, at least one digit appears before it. The value is rounded to the appropriate number of digits. (.) appears without a number following it, no decimal point is printed. g,GThe precision specifies the maximum number of significant digits printed. Six significant digits are printed, with any trailing zeros truncated. s,SThe precision specifies the maximum number of characters to be printed. Characters in excess of precision are not printed. Characters are printed until a null character is encountered. This slide adapted from information in MSDN Library 5/15/2015 ECE Application Programming: Lecture 4

10. 10 examples - printf() float a=67.49,b=9.999925; printf("Price:█%10f█%10f\n",a,b); printf("%8.2f█%8.4f█%5.1f█%7.5f\n",a,a,b,b); printf("a=%5.5f,█b=%0.2f\n",a,b); Printed: 00000000011111111112222222222333333 print 12345678901234567890123456789012345 position Price:██67.499000███9.999925 columns ███67.49██67.4900██10.0█9.99993 1 to 35 a=67.49000,█b=10.00 Note: On last line of output, the actual value was output; the printf routine overrode the specified width. 5/15/2015 ECE Application Programming: Lecture 4

11. 11 examples - printf() float a=67.49,b=9.999925; int i=184,j=-51; double x=123.456, y=-22.33; printf("%7.1lf%5d%8.2f\n",y,i,a); printf("%13.2f%4d%9.2lf\n",b,j,x); //changed Printed: 00000000011111111112222222222333333 print 12345678901234567890123456789012345 position -22.3 184 67.49 columns 10.00 -51 -22.33 1 to 35 Notes: d indicates decimal int eger f indicates float lf (that’s lower case L and f) indicates double (for double output, f OK too; not OK for input) 5/15/2015 ECE Application Programming: Lecture 4

12. 12 printf() examples printf("vv% dww%-dxx%+dyy%dzz\n",-12,-34,-56,-78);..../....1..../....2..../....3..../<= ruler vv-12ww-34xx-56yy-78zz printf("vv% dww%-dxx%+dyy%dzz\n",12,34,56,78);..../....1..../....2..../....3..../<= ruler vv 12ww34xx+56yy78zz printf("vv% 5dww%-5dxx%+5dyy%5dzz\n",-12,-34,-56,-78);..../....1..../....2..../....3..../<= ruler vv -12ww-34 xx -56yy -78zz printf("vv% 5dww%-5dxx%+5dyy%5dzz\n",12,34,56,78);..../....1..../....2..../....3..../<= ruler vv 12ww34 xx +56yy 78zz 5/15/2015 ECE Application Programming: Lecture 4

13. 13 printf() examples printf("v% 05dw%-05dx%+05dy%05dz\n",-12,-34,-56,-78);..../....1..../....2..../....3..../<= ruler v-0012w-34 x-0056y-0078z printf("v% 05dw%-05dx%+05dy%05dz\n",12,34,56,78);..../....1..../....2..../....3..../<= ruler v 0012w34 x+0056y00078z printf("v%7.3dw% 7.3dx%-7.3dy%+7.3dz\n",-12,-34,-56,-78);..../....1..../....2..../....3..../<= ruler v -012w -034x-056 y -078z print("v%7.3dw% 7.3dx%-7.3dy%+7.3dz\n", 12, 34, 56, 78);..../....1..../....2..../....3..../<= ruler v 012w 034x056 y +078z 5/15/2015 ECE Application Programming: Lecture 4

14. 14 printf() examples printf("w%7.2fx%7.2fy%7.2fz\n",-1.234,-3.456,-5.6);..../....1..../....2..../....3..../<= ruler w -1.23x -3.46y -5.60z printf("w%7.2fx%7.2fy%7.2fz\n", 1.234, 3.456, 5.6);..../....1..../....2..../....3..../<= ruler w 1.23w 3.46y 5.60z printf("w%7.2fx%7.2f\n",-1234567.8,1234567.8);..../....1..../....2..../....3..../<= ruler w-1234567.8x1234567.8z 5/15/2015 ECE Application Programming: Lecture 4

15. Example: Formatted output Assume int x = 123; float y = 4.56; double z = 7.89991 What does each of the following lines print?  printf("%4d %5f %6lf\n", x, y, z);  printf("%.4d %.4f %.4lf\n", x, y, z);  printf("%08d %-7.1f %+-4.1lf !\n", x, y, z); The second and third specifiers have precision of 1 One is a float (%f), the other is a double (%lf) 5/15/2015 ECE Application Programming: Lecture 5 15

16. Example solution printf("%4d %5f %6lf\n", x, y, z);  █123█4.560000█7.899910 printf("%.4d %.4f %.4lf\n", x, y, z);  0123█4.5600█7.8999 printf("%08d %-7.1f %+-4.1lf!\n", x, y, z);  00000123 █ 4.6 █████ +7.9 █ ! 5/15/2015 ECE Application Programming: Lecture 5 16

17. Example: Formatted output Write a short code sequence to do each of the following:  Print three integers—x, y, and z Use field widths of 10, 20, and 30, respectively Put an extra space between each field Show the signs of all values and left justify them  Print four double s—d1, d2, d3, d4 Use field widths of 7 for all values Put an extra space between each field Show 1, 2, 3, and 4 places after the decimal point, respectively  Given three variables— int w, p; double var; Read values for w and p from the input Print var using field width w and precision p 5/15/2015 ECE Application Programming: Lecture 5 17

18. Example solution Print three integers—x, y, and z  Use field widths of 10, 20, and 30, respectively  Put an extra space between each field  Show the signs of all values and left justify them printf(“%+-10d %+-20d %+-30d\n”, x, y, z); Print four double s—d1, d2, d3, d4  Use field widths of 7 for all values  Put an extra space between each field  Show 1, 2, 3, and 4 places after the decimal point, respectively printf(“%7.1lf %7.2lf %7.3lf %7.4lf\n”, d1, d2, d3, d4); 5/15/2015 ECE Application Programming: Lecture 5 18

19. Example solution (cont.) Given three variables— int w, p; double var;  Read values for w and p from the input  Print var using field width w and precision p scanf(“%d %d”, &w, &p); printf(“%*.*lf\n”, w, p, var); 5/15/2015 ECE Application Programming: Lecture 5 19

20. Next time Operators Conditional statements: if Reminders:  Program 2 due Wednesday, 2/6  Program 3 to be posted; due Wednesday, 2/13 5/15/2015 ECE Application Programming: Lecture 6 20