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C programming language assumes any non-zero and non-null values as true, and if it is either zero or null, then it is assumed as false value. C programming language provides the following types of decision making statements. C, or c, is the third letter in the English and ISO basic Latin alphabets.Its name in English is cee (pronounced / ˈ s iː /), plural cees.
Decision making structures require that the programmer specifies one or more conditions to be evaluated or tested by the program, along with a statement or statements to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.
Show below is the general form of a typical decision making structure found in most of the programming languages −
C programming language assumes any non-zero and non-null values as true, and if it is either zero or null, then it is assumed as false value.
C programming language provides the following types of decision making statements.
C-diff
| Sr.No. | Statement & Description |
|---|---|
| 1 | if statement An if statement consists of a boolean expression followed by one or more statements. |
| 2 | if...else statement An if statement can be followed by an optional else statement, which executes when the Boolean expression is false. |
| 3 | nested if statements You can use one if or else if statement inside another if or else if statement(s). |
| 4 | switch statement A switch statement allows a variable to be tested for equality against a list of values. |
| 5 | nested switch statements You can use one switch statement inside another switch statement(s). |
The ? : Operator
We have covered conditional operator ? : in the previous chapter which can be used to replace if...else statements. It has the following general form −
Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.
The value of a ? expression is determined like this −
C-span
Exp1 is evaluated. If it is true, then Exp2 is evaluated and becomes the value of the entire ? expression.
If Exp1 is false, then Exp3 is evaluated and its value becomes the value of the expression.
- The C Standard Library
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The stdio.h header defines three variable types, several macros, and various functions for performing input and output.
Library Variables
Following are the variable types defined in the header stdio.h −
| Sr.No. | Variable & Description |
|---|---|
| 1 | size_t This is the unsigned integral type and is the result of the sizeof keyword. |
| 2 | FILE This is an object type suitable for storing information for a file stream. |
| 3 | fpos_t This is an object type suitable for storing any position in a file. |
Library Macros
Following are the macros defined in the header stdio.h −
| Sr.No. | Macro & Description |
|---|---|
| 1 | NULL This macro is the value of a null pointer constant. |
| 2 | _IOFBF, _IOLBF and _IONBF These are the macros which expand to integral constant expressions with distinct values and suitable for the use as third argument to the setvbuf function. |
| 3 | BUFSIZ This macro is an integer, which represents the size of the buffer used by the setbuf function. |
| 4 | EOF This macro is a negative integer, which indicates that the end-of-file has been reached. |
| 5 | FOPEN_MAX This macro is an integer, which represents the maximum number of files that the system can guarantee to be opened simultaneously. |
| 6 | FILENAME_MAX This macro is an integer, which represents the longest length of a char array suitable for holding the longest possible filename. If the implementation imposes no limit, then this value should be the recommended maximum value. |
| 7 | L_tmpnam This macro is an integer, which represents the longest length of a char array suitable for holding the longest possible temporary filename created by the tmpnam function. |
| 8 | SEEK_CUR, SEEK_END, and SEEK_SET These macros are used in the fseek function to locate different positions in a file. |
| 9 | TMP_MAX This macro is the maximum number of unique filenames that the function tmpnam can generate. |
| 10 | stderr, stdin, and stdout These macros are pointers to FILE types which correspond to the standard error, standard input, and standard output streams. |
Library Functions
Following are the functions defined in the header stdio.h −
| Sr.No. | Function & Description |
|---|---|
| 1 | int fclose(FILE *stream) Closes the stream. All buffers are flushed. |
| 2 | void clearerr(FILE *stream) Clears the end-of-file and error indicators for the given stream. |
| 3 | int feof(FILE *stream) Tests the end-of-file indicator for the given stream. |
| 4 | int ferror(FILE *stream) Tests the error indicator for the given stream. |
| 5 | int fflush(FILE *stream) Flushes the output buffer of a stream. |
| 6 | int fgetpos(FILE *stream, fpos_t *pos) Gets the current file position of the stream and writes it to pos. |
| 7 | FILE *fopen(const char *filename, const char *mode) Opens the filename pointed to by filename using the given mode. |
| 8 | size_t fread(void *ptr, size_t size, size_t nmemb, FILE *stream) Reads data from the given stream into the array pointed to by ptr. |
| 9 | FILE *freopen(const char *filename, const char *mode, FILE *stream) Associates a new filename with the given open stream and same time closing the old file in stream. |
| 10 | int fseek(FILE *stream, long int offset, int whence) Sets the file position of the stream to the given offset. The argument offset signifies the number of bytes to seek from the given whence position. |
| 11 | int fsetpos(FILE *stream, const fpos_t *pos) Sets the file position of the given stream to the given position. The argument pos is a position given by the function fgetpos. |
| 12 | long int ftell(FILE *stream) Returns the current file position of the given stream. |
| 13 | size_t fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream) Writes data from the array pointed to by ptr to the given stream. |
| 14 | int remove(const char *filename) Deletes the given filename so that it is no longer accessible. |
| 15 | int rename(const char *old_filename, const char *new_filename) Causes the filename referred to, by old_filename to be changed to new_filename. |
| 16 | void rewind(FILE *stream) Sets the file position to the beginning of the file of the given stream. |
| 17 | void setbuf(FILE *stream, char *buffer) Defines how a stream should be buffered. |
| 18 | int setvbuf(FILE *stream, char *buffer, int mode, size_t size) Another function to define how a stream should be buffered. |
| 19 | FILE *tmpfile(void) Creates a temporary file in binary update mode (wb+). |
| 20 | char *tmpnam(char *str) Generates and returns a valid temporary filename which does not exist. |
| 21 | int fprintf(FILE *stream, const char *format, ...) Sends formatted output to a stream. |
| 22 | int printf(const char *format, ...) Sends formatted output to stdout. |
| 23 | int sprintf(char *str, const char *format, ...) Sends formatted output to a string. |
| 24 | int vfprintf(FILE *stream, const char *format, va_list arg) Sends formatted output to a stream using an argument list. |
| 25 | int vprintf(const char *format, va_list arg) Sends formatted output to stdout using an argument list. |
| 26 | int vsprintf(char *str, const char *format, va_list arg) Sends formatted output to a string using an argument list. |
| 27 | int fscanf(FILE *stream, const char *format, ...) Reads formatted input from a stream. |
| 28 | int scanf(const char *format, ...) Reads formatted input from stdin. |
| 29 | int sscanf(const char *str, const char *format, ...) Reads formatted input from a string. |
| 30 | int fgetc(FILE *stream) Gets the next character (an unsigned char) from the specified stream and advances the position indicator for the stream. |
| 31 | char *fgets(char *str, int n, FILE *stream) Reads a line from the specified stream and stores it into the string pointed to by str. It stops when either (n-1) characters are read, the newline character is read, or the end-of-file is reached, whichever comes first. |
| 32 | int fputc(int char, FILE *stream) Writes a character (an unsigned char) specified by the argument char to the specified stream and advances the position indicator for the stream. |
| 33 | int fputs(const char *str, FILE *stream) Writes a string to the specified stream up to but not including the null character. |
| 34 | int getc(FILE *stream) Gets the next character (an unsigned char) from the specified stream and advances the position indicator for the stream. |
| 35 | int getchar(void) Gets a character (an unsigned char) from stdin. |
| 36 | char *gets(char *str) Reads a line from stdin and stores it into the string pointed to by, str. It stops when either the newline character is read or when the end-of-file is reached, whichever comes first. |
| 37 | int putc(int char, FILE *stream) Writes a character (an unsigned char) specified by the argument char to the specified stream and advances the position indicator for the stream. |
| 38 | int putchar(int char) Writes a character (an unsigned char) specified by the argument char to stdout. |
| 39 | int puts(const char *str) Writes a string to stdout up to but not including the null character. A newline character is appended to the output. |
| 40 | int ungetc(int char, FILE *stream) Pushes the character char (an unsigned char) onto the specified stream so that the next character is read. |
| 41 | void perror(const char *str) Prints a descriptive error message to stderr. First the string str is printed followed by a colon and then a space. |