Programming Language B

Transcription

1 Programming Language B Takako Nemoto (JAIST) 10 December Takako Nemoto (JAIST) 10 December 1 / 15

2 Strings A string literal is a strings of characters included by double quotations. Examples String literals "ABC" "cde" "!?" Not string literals ABC cde" "!? In the memory location ( ), string literals are stored followed by the null character, which is written by \n. A B C \0 The null character indicates the end of the literal. It is assigned 0 in the system. Takako Nemoto (JAIST) 10 December 2 / 15

3 Some properties of string literals You can see that the size of string literals are (the length of the string)+1. This is because the null character in the end of the string. #include <stdio.h> printf("sizeof(\"123\") = %u\n", (unsigned)sizeof("123")); printf("sizeof(\"ab\\tc\") = %u\n", (unsigned)sizeof("ab\tc")); printf("sizeof(\"abc\\0def\") = %u\n", (unsigned)sizeof("abc\0def")); String literals has static strage duration. It depends on the system if the two literals in the following function func are stored as A B C \0 or void func(void){ puts("abc"); puts("abc");} A B C \0 A B C \0 Takako Nemoto (JAIST) 10 December 3 / 15

4 String and initialization Strings are sequence of characters. Usually, strings are stored as arrays of type char. A B C \0 Caution "ABC" is a string and a string literal. "AB\0C" is a not a string but a string literal. Takako Nemoto (JAIST) 10 December 4 / 15

5 Two ways of initialization of strings #include <stdio.h> //9-2.c char str[4]; str[0] = 'A'; str[1] = 'B'; str[2] = 'C'; str[3] = '\0'; printf("str = \"%s\".\n", str); #include <stdio.h> //9-3.c char str[] = "ABC"; printf("str = \"%s\".\n", str); char str[]="abc"; is same as char str[]={'a', 'B', 'C','\0'}; But we can not asign by char s[4]; s = {'A', 'B', 'C','\0'}; s = "ABC"; Takako Nemoto (JAIST) 10 December 5 / 15

6 Two ways of initialization of strings #include <stdio.h> //9-2.c char str[4]; str[0] = 'A'; str[1] = 'B'; str[2] = 'C'; str[3] = '\0'; printf("str = \"%s\".\n", str); #include <stdio.h> //9-3.c char str[] = "ABC"; printf("str = \"%s\".\n", str); Exercise Change "ABC" into "ABC\0DEF" in 9-3.c and run the modified program. What output do you have? Takako Nemoto (JAIST) 10 December 6 / 15

7 Two ways of initialization of strings #include <stdio.h> //9-2.c char str[4]; str[0] = 'A'; str[1] = 'B'; str[2] = 'C'; str[3] = '\0'; printf("str = \"%s\".\n", str); #include <stdio.h> //9-3.c char str[] = "ABC"; printf("str = \"%s\".\n", str); We can initialize str[] by the null string as follows: char str[] = ""; or char str[] = {\0}; Takako Nemoto (JAIST) 10 December 7 / 15

8 Scan of strings #include <stdio.h> //9-4.c } char name[48]; printf("what's your name?\n"); scanf("%s", name); printf("hi! %s!!\n", name); return 0; %s is the conversion specification for strings. Note that & is NOT needed in front of name in scanf. Takako Nemoto (JAIST) 10 December 8 / 15

9 Formatting of strings #include <stdio.h> //9-5.c char str[] = "12345"; } printf("%s\n", str); printf("%3s\n", str); printf("%.3s\n", str); printf("%8s\n", str); printf("%-8s\n", str); return 0; % 9. 9 s %A..B C A. The minimum width of the field B. Precision (maximum digits here) C. Conversion specifier Takako Nemoto (JAIST) 10 December 9 / 15

10 Arrays of strings #include <stdio.h> //9-7.c int i; char s[3][128]; for(i = 0; i < 3; i++){ printf("s[%d]: ", i); scanf("%s", s[i]); } } for (i = 0; i < 3; i++) printf("s[%d] = \"%s\"\n",i, s[i]); return 0; Takako Nemoto (JAIST) 10 December 10 / 15

11 Operation for strings #include <stdio.h> //9-8.c int str_length(const char s[]) { int len = 0; while (s[len]) len++; return len; } int main(void) { char str[128]; printf("input a string: "); scanf("%s", str); printf("the length of the string \"%s\" is %d.\n", str, str_length(str)); Takako Nemoto (JAIST) 10 December 11 / 15

12 Usage of putchar #include <stdio.h> //9-9.c void put_string(const char s[]){ int i = 0; while(s[i]) putchar(s[i++]);} char str[128]; printf("input a string: "); scanf("%s", str); printf("your input is "); put_string(str); printf(".\n"); Takako Nemoto (JAIST) 10 December 12 / 15

13 #include <ctype.h> //9-11.c, Conversion of upper & lower characters #include <stdio.h> void str_toupper(char s[]){ int i = 0; while (s[i]){ s[i] = toupper(s[i]); i++;}} void str_tolower(char s[]){ int i = 0; while (s[i]){ s[i] = tolower(s[i]); i++;}} char str[128]; printf("input a string:\n"); scanf("%s", str); str_toupper(str); printf("%s\n", str); str_tolower(str); printf("%s\n", str); Takako Nemoto (JAIST) 10 December 13 / 15

14 Some more example #include <stdio.h> void put_strary(const char s[][6], int n){ int i; for (i = 0; i < n; i++) printf("s[%d] = \"%s\"\n", i, s[i]); } char cs[][6] = {"Turbo", "NA", "DOHC"}; put_strary(cs, 3); } return 0; Takako Nemoto (JAIST) 10 December 14 / 15

15 Today s homework 1 Do Exercise 9-5 ( 9-5) in p.249 (in the latest edition). The type of second argument of str_char coud be changed. Make also the function main so that to input the string and the character you want to search and to print the result. 2 Do Exercise 9-9 ( 9-9) in p.251 (in the latest edition). Make also the function main so that to input the string and to print the result. 3 Make a function convert_up_low(char s[]) s.t. it converts lower characters into upper ones and upper characters into lower ones in a string. Make also the function main so that to input the string and to print the result. As usual, send the programs and the text file as attached files to me via , with the title Homework Lecture 10 by the next lecture. Please make sure to include your name and student ID number. Takako Nemoto (JAIST) 10 December 15 / 15