STRINGS. If you follow the rule of array initialization then you can write the above statement as follows:

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Loren Goodwin
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1 STRINGS The string in C programming language is actually a one-dimensional array of characters which is terminated by a null character '\0'. Thus a null-terminated string contains the characters that comprise the string followed by a null. The following declaration and initialization create a string consisting of the word "Hello". To hold the null character at the end of the array, the size of the character array containing the string is one more than the number of characters in the word "Hello." char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'; If you follow the rule of array initialization then you can write the above statement as follows: char greeting[] = "Hello"; Following is the memory presentation of above defined string in C/C++: Actually, you do not place the null character at the end of a string constant. The C compiler automatically places the '\0' at the end of the string when it initializes the array. Let us try to print above mentioned string: #include <stdio.h> int main () { char greeting[6] = {'H', 'e', 'l', 'l', 'o', '\0'; printf("greeting message: %s\n", greeting ); return 0; When the above code is compiled and executed, it produces result something as follows: Greeting message: Hello

2 C supports a wide range of functions that manipulate null-terminated strings: S.N Function & Purpose strcpy(s1, s2); Copies string s2 into string s1. strcat(s1, s2); Concatenates string s2 onto the end of string s1. strlen(s1); Returns the length of string s1. strcmp(s1, s2); Returns 0 if s1 and s2 are the same; less than 0 if s1<s2; greater than 0 if s1>s2. strchr(s1, ch); Returns a pointer to the first occurrence of character ch in string s1. strstr(s1, s2); Returns a pointer to the first occurrence of string s2 in string s1. Following example makes use of few of the above-mentioned functions: #include <stdio.h> #include <string.h> int main () { char str1[12] = "Hello"; char str2[12] = "World"; char str3[12]; int len ; /* copy str1 into str3 strcpy(str3, str1); printf("strcpy( str3, str1) : %s\n", str3 ); /* concatenates str1 and str2 strcat( str1, str2); printf("strcat( str1, str2): %s\n", str1 ); /* total lenghth of str1 after concatenation len = strlen(str1); printf("strlen(str1) : %d\n", len ); return 0; When the above code is compiled and executed, it produces result something as follows: strcpy( str3, str1) : Hello strcat( str1, str2): HelloWorld strlen(str1) : 10

3 STRINGS in C string: array of characters terminated by NULL character string in/output: printf("%s",s), scanf("%s",s) string.h : collection of functions for string manipulation no standard operators for string assignment and comparisons! (remember: strings are arrays!) Arrays of Characters /* strings are array of characters * terminated by the NULL character * which is different from '0' char S[MAX_STRING_LEN]; int l, i; S[0] = 'a'; S[1] = 'b'; S[2] = 'c'; S[3] = 'd'; S[4] = 'e'; S[5] = 'g'; S[6] = '0'; S[7] = 0; l = strlen(s); printf("s:\t%s\n",s); printf("length:\t%d\n",l); /* print characters in S printf("forward\n"); for (i = 0; i < l; ++i) printf("a[%d] = %c\n",i,s[i]); /* print characters in S backwards printf("\nbackward\n"); for (i = l-1; i >= 0; --i)

4 printf("a[%d] = %c\n",i,s[i]); String IO /* strings can be read using scanf with %s * string.h contains many useful functions * for working with strings: * strcmp for string comparisons * strcpy to copy strings *... * * Check what happens if your input contains * spaces, tabs, etc * char S1[MAX_STRING_LEN]; char S2[MAX_STRING_LEN]; int i, l; printf("string:\t"); scanf("%s",s1); /* we need to copy all the characters, and * the final NULL character! l = strlen(s1); /* rather than writing this loop we could also write strcpy(s2,s1) for (i = 0; i < l+1; ++i) S2[i] = S1[i]; /* change original S1 S1[0] = S1[1] = S1[2] = '*'; S1[3] = 0; /* print both strings

5 String Comparison /* What is the result of the following * for different strings S1, S2? char S1[MAX_STRING_LEN]; char S2[MAX_STRING_LEN]; int i, l, res; printf("string1:\t"); scanf("%s",s1); printf("string2:\t"); scanf("%s",s2); res = strcmp(s1,s2); printf("strcmp(%ss1,%ss2) = %d\n",s1,s2,res); Copying Strings /* Warning: Strings aren't regular variables * You've to be careful with string comparison * and assignments. char* S1 = "AAAAAAAAAA"; char* S2 = "BBBBBBBBBB"; int i, l; /* assign S1 to S2 S2 = S1; /* change S1 S1[0] = S1[1] = S1[2] = '*';

6 S1[3] = 0; /* print both strings Equality of Strings /* Warning: Strings aren't regular variables * You've to be careful with string comparison * and assignments. char* S1 = "AAAAAAAAAA"; char* S2 = "AAAAAAAAAA"; int cmp1, cmp2, cmp3, cmp4; cmp1 = (S1 == S2); cmp2 = strcmp(s1,s2); printf("s1 == S2:\t%d\n",cmp1); printf("strcmp(s1,s2):\t%d\n",cmp2); S2 = S1; cmp3 = (S1 == S2); cmp4 = strcmp(s1,s2); printf("\nafter assignment\n"); printf("s1 == S2:\t%d\n",cmp3); printf("strcmp(s1,s2):\t%d\n",cmp4); Strcat #define MAX_STRING_LENGTH 80 /* strcat is another useful command:

7 * it appends a copy of a second string char S1[MAX_STRING_LENGTH]; char S2[MAX_STRING_LENGTH]; strcat(s1,s2); printf("s1:\t"); scanf("%s",s1); printf("s2:\t"); scanf("%s",s2); strcat(s1,s2); printf("\nafter strcat(s1,s2)\n");

ASCII Encoding. The char Type. Manipulating Characters. Manipulating Characters

ASCII Encoding. The char Type. Manipulating Characters. Manipulating Characters The char Type ASCII Encoding The C char type stores small integers. It is usually 8 bits. char variables guaranteed to be able to hold integers 0.. +127. char variables mostly used to store characters