`int printf(const char *format, ...)`- The
`printf`function provides formatted output conversion. `int scanf(const char *format, ...)``atof`converts`s`to`double`.`int atoi(const char *s)`- converts
`s`to`int`. `int rand(void)``rand`returns a pseudo-random integer in the range 0 to`RAND_MAX`, which is at least 32767.`void srand(unsigned int seed)``srand`uses`seed`as the seed for a new sequence of pseudo-random numbers. The initial seed is 1.`void *malloc(size_t size)``malloc`returns a pointer to space for an object of size`size`, or`NULL`if the request cannot be satisfied. The space is uninitialized.`void free(void *p)``free`deallocates the space pointed to by`p`; it does nothing if`p`is`NULL`.`p`must be a pointer to space previously allocated by`malloc`.`int abs(int n)``abs`returns the absolute value of its`int`argument.`time_t time(time_t *tp)``time`returns the current calendar time or`-1`if the time is not available. If`tp`is not`NULL`, the return value is also assigned to`*tp`.

- The

In the following table, variables `s` is of type
`char *`; `cs` and `ct` are of type `const char *`;
and `c` is an `int`
converted to `char`.

char *strcpy(s,ct) |
copy string ct to string s, including '\0';
return s. |

char *strcat(s,ct) |
concatenate string ct to end of string s; return
s. |

int strcmp(cs,ct) |
compare string cs to string ct, return <0 if
cs<ct, 0 if cs==ct, or >0 if cs>ct. |

char *strchr(cs,c) |
return pointer to first occurrence of c in cs or
NULL if not present. |

char *strstr(cs,ct) |
return pointer to first occurrence of string ct in
cs, or NULL if not present. |

size_t strlen(cs) |
return length of cs. |

In the following
table, `s` is of type `void *`;
`ct` is of type `const void *`; `n` is of type
`size_t`; and `c` is an `int` converted to an `unsigned
char`.

void *memcpy(s,ct,n) |
copy n characters from ct to s, and return
s. |

void *memset(s,c,n) |
place character c into first n characters of
s, return s. |

In the following table, `x` and `y` are of type
`double`, and all functions return
`double`.

exp(x) |
exponential function e^{x} |

log(x) |
natural logarithm ln(x), x>0. |

log10(x) |
base 10 logarithm log_{10}(x), x>0. |

pow(x,y) |
x. A domain error occurs if ^{y}x=0 and
y<=0, or if x<0 and y is not an
integer. |

sqrt(x) |
square root of x, x>=0. |

fabs(x) |
absolute value |x| |