c  go  java  js  lua  py  vbs  rkt  scm  pro  

This page looks at the string as a character array and endfile loop processing.

Note: For example purposes, declarations, input, processing, and output will not be separated in the following program.

In all cases, the output is exactly the same.

C has a string library.
#include <string.h>

Here is one way to represent the string "A bad cat.".
char a1[256] = "A bad cat."; int alen1; alen1 = strlen(a1); printf("a: %s [%d characters]\n",a1,alen1);
The strlen function from the string.h library returns the length of a string.

A string in C is an array of characters. A character array literal can be used as a string, but the terminating null byte (zero) must be included at the end.
char b1[256] = {'A', ' ', 'b', 'a', 'd', ' ', 'c', 'a', 't', '.', '\0'}; int blen1; blen1 = strlen(b1); printf("b: %s [%d characters]\n",b1,blen1);

A string can be input from the standard input.
char c1[256]; int clen1; scanf("%[^\n]s",&c1); clen1 = strlen(c1); printf("c: %s [%d characters]\n",c1,clen1);

The string c1 can be processed (after input using scanf) explicitly, character by character, as follows.
int dpos1; int dlen1; dlen1 = 0; while (c1[dlen1] != 0) { dlen1++; } printf("d: "); for (int dpos1=0; dpos1 < dlen1; dpos1++) { printf("%c",c1[dpos1]); } printf(" [%d characters]",dlen1);

Here is the C code.
#include <stdio.h> #include <string.h> int main() { char a1[256] = "A bad cat."; int alen1; alen1 = strlen(a1); printf("a: %s [%d characters]\n",a1,alen1); char b1[256] = {'A', ' ', 'b', 'a', 'd', ' ', 'c', 'a', 't', '.', '\0'}; int blen1; blen1 = strlen(b1); printf("b: %s [%d characters]\n",b1,blen1); char c1[256]; int clen1; scanf("%[^\n]s",&c1); clen1 = strlen(c1); printf("c: %s [%d characters]\n",c1,clen1); int dpos1; int dlen1; dlen1 = 0; while (c1[dlen1] != 0) { dlen1++; } printf("d: "); for (int dpos1=0; dpos1 < dlen1; dpos1++) { printf("%c",c1[dpos1]); } printf(" [%d characters]",dlen1); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
A bad cat.
For the above example input, here is the expected output.
a: A bad cat. [10 characters] b: A bad cat. [10 characters] c: A bad cat. [10 characters] d: A bad cat. [10 characters]

Here is a program that explicitly reads in a string, character by character, until the end of file is detected.

Here is the C code.
#include <stdio.h> int main() { // declarations char ch1; char s1[256]; int slen1; // input slen1 = 0; scanf("%c",&ch1); while (! feof(stdin)) { s1[slen1] = ch1; slen1++; scanf("%c",&ch1); } // add the null byte s1[slen1] = 0; printf("%s [%d characters]\n",s1,slen1); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
A bad cat.
For the above example input, here is the expected output.
A bad cat. [10 characters]

We can write our own string length function as follows.
int rsStrLen1(char s1[]) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; }
The function strlen in string.h is a similar function. Do you see how the rsStrLen function could not work right if the zero byte is not at the end? This and related issues make string processing tedious and hard to get always correct in languages such as C.

In C, the keyword const is a hint to the compiler that this variable is not allowed to be changed. We can use that in the above function rsStrLen1 to get function rsStrLen2 as follows.
int rsStrLen2(const char s1[]) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; }

As if the above is not confusing enough, in C one can use a pointer as a formal parameter instead of empty array brackets as follows.
int rsStrLen3(char *s1) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; }
Here is the const version using a pointer formal parameter.
int rsStrLen4(const char *s1) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; }
Remember, the const keyword means that the variable is a pseudo-constant and cannot be changed. Note: In all of the above four functions, the body is exactly the same. What has changed is the formal parameter signature.

Rule: Arrays are always passed by reference. But a variable passed by reference as a pointer can be accessed as an array. This can cause bizarre behavior if the passed variable is not actually an array. See Arrays and lack of bounds checking .

Here then is a program that explicitly reads in a string, character by character, until the end of file is detected.

Here is the C code.
#include <stdio.h> #include <string.h> int rsStrLen1(char s1[]) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; } int rsStrLen2(const char s1[]) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; } int rsStrLen3(char *s1) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; } int rsStrLen4(const char *s1) { int n1 = 0; while (s1[n1] != 0) { n1++; } return n1; } int main() { char c1[256]; int clen1; scanf("%[^\n]s",&c1); clen1 = strlen(c1); printf("c: %s [%d characters]\n",c1,clen1); int dlen1; dlen1 = rsStrLen1(c1); printf("d: %s [%d characters]\n",c1,dlen1); dlen1 = rsStrLen2(c1); printf("d: %s [%d characters]\n",c1,dlen1); dlen1 = rsStrLen3(c1); printf("d: %s [%d characters]\n",c1,dlen1); dlen1 = rsStrLen4(c1); printf("d: %s [%d characters]\n",c1,dlen1); return 0; }

Here are some examples of input and output for the above program code.

Here is an example input.
A bad cat.
For the above example input, here is the expected output.
c: A bad cat. [10 characters] d: A bad cat. [10 characters] d: A bad cat. [10 characters] d: A bad cat. [10 characters] d: A bad cat. [10 characters]