Exercise 7 Strings

An array of characters Used to store text Another way to initialize: char A[ ]=“blabla”;

The Terminator Strings terminate with NULL character, signed by ‘\0’ (ascii code 0) This is a convention used to know where the string ends It means that in order to hold a string of 7 chars we need an array of length 8 So the previous initialization is equivalent to char A[ ] = {‘b’, ‘l’, ‘a’, ‘b’, ‘l’, ‘a’, ‘\0’};

The fool on the null #include int main(void) { char str[]="I'm a full string"; printf("%s\n", str); str[7]='o'; str[8]='o'; printf("%s\n", str); str[11]='\0'; printf("%s\n", str); str[11] = ‘s’; printf("%s\n", str); return 0; }

Reading-in strings There are several ways of accepting strings as input from the user The obvious way to go is read character by character using getchar()

Example Read_String_with_getchar.c

Reading-in strings: scanf A simpler way is to use scanf To read in a string to a variable str, write :  scanf(“%s”, str);  Note there’s no ‘&’ sign!!!

Reading-in strings - scanf scanf reads-in letters until a space or newline (‘\n’) is encountered The maximum length can be stated in the parentheses:  scanf(“%10s”, str);  This will read in 10 letters, plus the ‘\0’ sign (so str should have place for 11 characters)

Example Read_String_with_scanf.c

Comparing strings We cannot just compare strings’ contents by == char A[7]=“Hello”; char B[7]=“Hello”; if (A==B) {... } Because A and B are addresses of A[0] and B[0] A==B only if A and B are the same string in memory In order to compare the contents we must scan char by char ‘H’‘e’‘l’ ‘o’‘\0’…. B ‘H’‘e’‘l’ ‘o’‘\0’…. A

Example Compare.c

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 0 i ‘Y’‘e’‘w’‘\0’ A

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 0 i ‘Y’‘e’‘w’‘\0’ A

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘w’‘\0’ A

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘w’‘\0’ A

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 2 i ‘Y’‘e’‘w’‘\0’ A

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 2 i ‘Y’‘e’‘w’‘\0’ A

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 2 i ‘Y’‘e’‘w’‘\0’ A

Compare – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 2 i ‘Y’‘e’‘w’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 0 i ‘Y’‘e’‘s’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 0 i ‘Y’‘e’‘s’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘s’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘s’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 2 i ‘Y’‘e’‘s’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 2 i ‘Y’‘e’‘s’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 3 i ‘Y’‘e’‘s’‘\0’ A

Equal strings – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 3 i ‘Y’‘e’‘s’‘\0’ A

Different length – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 0 i ‘Y’‘e’‘\0’ A

Different length – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 0 i ‘Y’‘e’‘\0’ A

Different length – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘\0’ A

Different length – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘\0’ A

Different length – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 2 i ‘Y’‘e’‘\0’ A

Different length – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘\0’ A

Different length – step by step for(i=0; A[i]!='\0' || B[i]!='\0'; i++) if(A[i]!=B[i]) { printf("A is different from B!\n"); return 0; } printf("A and B are the same!\n"); return 0; B ‘Y’‘e’‘s’‘\0’ 1 i ‘Y’‘e’‘\0’ A

String library Like in the case of stdio.h and math.h, we have a special library for handling strings We should #include string.h Functions:  strlen(s) – returns the length of s  strcmp(s1, s2) – compares s1 with s2  strcpy(s1, s2) – copies to contents of s2 to s1  and more…

Example easy_compare.c

If there’s time… Exercise: write a program that:  gets an input string from the user (up to 100 chars, no white spaces)  gets 2 characters from the user  replaces each occurrence of the first character in the string by the second character, and prints the result. Example:  input: “papa”, ‘p’, ‘m’  output: “mama”

Solution replace.c

If there’s time… Exercise: write a function:  void my_to_lower(char str[]);  The function receives an arbitrary string and converts all its letters to lower-case letters Demonstrate the use of your function by some example that prints the input and output on the screen