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Several functions from <ctype.h> perform character tests and conversions. In the following, c is an int that can be represented as an unsigned char or EOF. The function returns int. (more…)

The standard library provides a rather restricted version of the function ungetch that we wrote in Chapter 4; it is called ungetc.

   int ungetc(int c, FILE *fp)
pushes the character c back onto file fp, and returns either c, or EOF for an error. Only one character of pushback is guaranteed per file. ungetc may be used with any of the input functions like scanf, getc, or getchar.

The function system(char *s) executes the command contained in the character string s, then resumes execution of the current program. The contents of s depend strongly on the local operating system. As a trivial example, on UNIX systems, the statement

   system(”date”);
causes the program date to be run; it prints the date and time of day on the standard output. system returns a system-dependent integer status from the command executed. In the UNIX system, the status return is the value returned by exit.

The functions malloc and calloc obtain blocks of memory dynamically.

   void *malloc(size_t n)
returns a pointer to n bytes of uninitialized storage, or NULL if the request cannot be satisfied. (more…)