函数名: abs 功 能: 求整数的绝对值
用 法: int abs(int i);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
int number = -1234;
printf("number: %d absolute value: %d/n", number, abs(number));
return 0;
}
函数名: atof
功 能: 把字符串转换成浮点数
用 法: double atof(const char *nptr);
程序例:
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
float f;
char *str = "12345.67";
f = atof(str);
printf("string = %s float = %f/n", str, f);
return 0;
}
函数名: atoi
功 能: 把字符串转换成长整型数
用 法: int atoi(const char *nptr);
程序例:
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
int n;
char *str = "12345.67";
n = atoi(str);
printf("string = %s integer = %d/n", str, n);
return 0;
}
函数名: atol
功 能: 把字符串转换成长整型数
用 法: long atol(const char *nptr);
程序例:
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
long l;
char *str = "98765432";
l = atol(lstr);
printf("string = %s integer = %ld/n", str, l);
return(0);
}
函数名: bsearch
功 能: 二分法搜索
用 法: void *bsearch(const void *key, const void *base, size_t *nelem, size_t width, int(*fcmp)(const void *, const *));
程序例:
#include <stdlib.h>
#include <stdio.h>
#define NELEMS(arr) (sizeof(arr) / sizeof(arr[0]))
int numarray[] = {123, 145, 512, 627, 800, 933};
int numeric (const int *p1, const int *p2)
{
return(*p1 - *p2);
}
int lookup(int key)
{
int *itemptr;
/* The cast of (int(*)(const void *,const void*))
is needed to avoid a type mismatch error at
compile time */
itemptr = bsearch (&key, numarray, NELEMS(numarray),
sizeof(int), (int(*)(const void *,const void *))numeric);
return (itemptr != NULL);
}
int main(void)
{
if (lookup(512))
printf("512 is in the table./n");
else
printf("512 isn't in the table./n");
return 0;
}
函数名: ceil
功 能: 向上舍入
用 法: double ceil(double x);
程序例:
#include <math.h>
#include <stdio.h>
int main(void)
{
double number = 123.54;
double down, up;
down = floor(number);
up = ceil(number);
printf("original number %5.2lf/n", number);
printf("number rounded down %5.2lf/n", down);
printf("number rounded up %5.2lf/n", up);
return 0;
}
函数名: div 功 能: 将两个整数相除, 返回商和余数
用 法: div_t (int number, int denom);
程序例:
#include <stdlib.h>
#include <stdio.h>
div_t x;
int main(void)
{
x = div(10,3);
printf("10 div 3 = %d remainder %d/n", x.quot, x.rem);
return 0;
}
函数名: ecvt
功 能: 把一个浮点数转换为字符串
用 法: char ecvt(double value, int ndigit, int *decpt, int *sign);
程序例:
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
int main(void)
{
char *string;
double value;
int dec, sign;
int ndig = 10;
clrscr();
value = 9.876;
string = ecvt(value, ndig, &dec, &sign);
printf("string = %s dec = %d /
sign = %d/n", string, dec, sign);
value = -123.45;
ndig= 15;
string = ecvt(value,ndig,&dec,&sign);
printf("string = %s dec = %d sign = %d/n",
string, dec, sign);
value = 0.6789e5; /* scientific
notation */
ndig = 5;
string = ecvt(value,ndig,&dec,&sign);
printf("string = %s dec = %d/
sign = %d/n", string, dec, sign);
return 0;
}
函数名: exp 功 能: 指数函数
用 法: double exp(double x);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
double result;
double x = 4.0;
result = exp(x);
printf("'e' raised to the power /
of %lf (e ^ %lf) = %lf/n",
x, x, result);
return 0;
}
函数名: fabs
功 能: 返回浮点数的绝对值
用 法: double fabs(double x);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
float number = -1234.0;
printf("number: %f absolute value: %f/n",
number, fabs(number));
return 0;
}
函数名: fcvt
功 能: 把一个浮点数转换为字符串
用 法: char *fcvt(double value, int ndigit, int *decpt, int *sign);
程序例:
#include <stdlib.h>
#include <stdio.h>
#include <conio.h>
int main(void)
{
char *string;
double value;
int dec, sign;
int ndig = 10;
clrscr();
value = 9.876;
string = ecvt(value, ndig, &dec, &sign);
printf("string = %s dec = %d /
sign = %d/n", string, dec, sign);
value = -123.45;
ndig= 15;
string = ecvt(value,ndig,&dec,&sign);
printf("string = %s dec = %d sign = %d/n",
string, dec, sign);
value = 0.6789e5; /* scientific
notation */
ndig = 5;
string = ecvt(value,ndig,&dec,&sign);
printf("string = %s dec = %d/
sign = %d/n", string, dec, sign);
return 0;
}
函数名: floor
功 能: 向下舍入
用 法: double floor(double x);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
double number = 123.54;
double down, up;
down = floor(number);
up = ceil(number);
printf("original number %10.2lf/n",
number);
printf("number rounded down %10.2lf/n",
down);
printf("number rounded up %10.2lf/n",
up);
return 0;
}
函数名: fmod
功 能: 计算x对y的模, 即x/y的余数
用 法: double fmod(double x, double y);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
double x = 5.0, y = 2.0;
double result;
result = fmod(x,y);
printf("The remainder of (%lf / %lf) is /
%lf/n", x, y, result);
return 0;
}
函数名: gcvt
功 能: 把浮点数转换成字符串
用 法: char *gcvt(double value, int ndigit, char *buf);
程序例:
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
char str[25];
double num;
int sig = 5; /* significant digits */
/* a regular number */
num = 9.876;
gcvt(num, sig, str);
printf("string = %s/n", str);
/* a negative number */
num = -123.4567;
gcvt(num, sig, str);
printf("string = %s/n", str);
/* scientific notation */
num = 0.678e5;
gcvt(num, sig, str);
printf("string = %s/n", str);
return(0);
}
函数名: itoa
功 能: 把一整数转换为字符串
用 法: char *itoa(int value, char *string, int radix);
程序例:
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
int number = 12345;
char string[25];
itoa(number, string, 10);
printf("integer = %d string = %s/n", number, string);
return 0;
}
函数名: labs
功 能: 取长整型绝对值
用 法: long labs(long n);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
long result;
long x = -12345678L;
result= labs(x);
printf("number: %ld abs value: %ld/n",
x, result);
return 0;
}
函数名: ldexp
功 能: 计算value*2的幂
用 法: double ldexp(double value, int exp);
程序例:
#include <stdio.h>
#include <math.h>
int main(void)
{
double value;
double x = 2;
/* ldexp raises 2 by a power of 3
then multiplies the result by 2 */
value = ldexp(x,3);
printf("The ldexp value is: %lf/n",
value);
return 0;
}
函数名: ldiv
功 能: 两个长整型数相除, 返回商和余数
用 法: ldiv_t ldiv(long lnumer, long ldenom);
程序例:
/* ldiv example */
#include <stdlib.h>
#include <stdio.h>
int main(void)
{
ldiv_t lx;
lx = ldiv(100000L, 30000L);
printf("100000 div 30000 = %ld remainder %ld/n", lx.quot, lx.rem);
return 0;
}
函数名: lfind
功 能: 执行线性搜索
用 法: void *lfind(void *key, void *base, int *nelem, int width, int (*fcmp)());
程序例:
#include <stdio.h>
#include <stdlib.h>
int compare(int *x, int *y)
{
return( *x - *y );
}
int main(void)
{
int array[5] = {35, 87, 46, 99, 12};
size_t nelem = 5;
int key;
int *result;
key = 99;
result = lfind(&key, array, &nelem,
sizeof(int), (int(*)(const void *,const void *))compare);
if (result)
printf("Number %d found/n",key);
else
printf("Number %d not found/n",key);
return 0;
}
函数名: log 功 能: 对数函数ln(x)
用 法: double log(double x);
程序例:
#include <math.h>
#include <stdio.h>
int main(void)
{
double result;
double x = 8.6872;
result = log(x);
printf("The natural log of %lf is %lf/n", x, result);
return 0;
}
函数名: log10
功 能: 对数函数log
用 法: double log10(double x);
程序例:
#include <math.h>
#include <stdio.h>
int main(void)
{
double result;
double x = 800.6872;
result = log10(x);
printf("The common log of %lf is %lf/n", x, result);
return 0;
}
函数名: lsearch
功 能: 线性搜索用 法: void *lsearch(const void *key, void *base, size_t *nelem, size_t width, int (*fcmp)(const void *, const void *));
程序例:
#include <stdio.h>
#include <stdlib.h>
int compare(int *x, int *y)
{
return( *x - *y );
}
int main(void)
{
int array[5] = {35, 87, 46, 99, 12};
size_t nelem = 5;
int key;
int *result;
key = 99;
result = lfind(&key, array, &nelem,
sizeof(int), (int(*)(const void *,const void *))compare);
if (result)
printf("Number %d found/n",key);
else
printf("Number %d not found/n",key);
return 0;
}
函数名: memcpy
功 能: 从源source中拷贝n个字节到目标destin中
用 法: void *memcpy(void *destin, void *source, unsigned n);
程序例:
#include <stdio.h>
#include <string.h>
int main(void)
{
char src[] = "******************************";
char dest[] = "abcdefghijlkmnopqrstuvwxyz0123456709";
char *ptr;
printf("destination before memcpy: %s/n", dest);
ptr = memcpy(dest, src, strlen(src));
if (ptr)
printf("destination after memcpy: %s/n", dest);
else
printf("memcpy failed/n");
return 0;
}
函数名: memset
功 能: 设置s中的所有字节为ch, s数组的大小由n给定
用 法: void *memset(void *s, char ch, unsigned n);
程序例:
#include <string.h>
#include <stdio.h>
#include <mem.h>
int main(void)
{
char buffer[] = "Hello world/n";
printf("Buffer before memset: %s/n", buffer);
memset(buffer, '*', strlen(buffer) - 1);
printf("Buffer after memset: %s/n", buffer);
return 0;
}
函数名: pow 功 能: 指数函数(x的y次方)
用 法: double pow(double x, double y);
程序例:
#include <math.h>
#include <stdio.h>
int main(void)
{
double x = 2.0, y = 3.0;
printf("%lf raised to %lf is %lf/n", x, y, pow(x, y));
return 0;
}
函数名: pow10
功 能: 指数函数(10的p次方)
用 法: double pow10(int p);
程序例:
#include <math.h>
#include <stdio.h>
int main(void)
{
double p = 3.0;
printf("Ten raised to %lf is %lf/n", p, pow10(p));
return 0;
}
函数名: qsort
功 能: 使用快速排序例程进行排序 用 法: void qsort(void *base, int nelem, int width, int (*fcmp)());
程序例: #include <stdio.h>
#include <stdlib.h>
#include <string.h>
int sort_function( const void *a, const void *b);
char list[5][4] = { "cat", "car", "cab", "cap", "can" };
int main(void)
{
int x;
qsort((void *)list, 5, sizeof(list[0]), sort_function);
for (x = 0; x < 5; x++)
printf("%s/n", list[x]);
return 0;
}
int sort_function( const void *a, const void *b)
{
return( strcmp(a,b) );
} 函数名: sqrt 功 能: 计算平方根 用 法: double sqrt(double x); 程序例: #include <math.h> #include <stdio.h> int main(void) { double x = 4.0, result; result = sqrt(x); printf("The square root of %lf is %lf/n", x, result); return 0; } 函数名: sscanf 功 能: 执行从字符串中的格式化输入 用 法: int sscanf(char *string, char *format[,argument,...]); 程序例: #include <stdio.h> #include <conio.h> int main(void) { char label[20]; char name[20]; int entries = 0; int loop, age; double salary; struct Entry_struct { char name[20]; int age; float salary; } entry[20]; /* Input a label as a string of characters restricting to 20 characters */ printf("/n/nPlease enter a label for the chart: "); scanf("%20s", label); fflush(stdin); /* flush the input stream in case of bad input */ /* Input number of entries as an integer */ printf("How many entries will there be? (less than 20) "); scanf("%d", &entries); fflush(stdin); /* flush the input stream in case of bad input */ /* input a name restricting input to only letters upper or lower case */ for (loop=0;loop<entries;++loop) { printf("Entry %d/n", loop); printf(" Name : "); scanf("%[A-Za-z]", entry[loop].name); fflush(stdin); /* flush the input stream in case of bad input */ /* input an age as an integer */ printf(" Age : "); scanf("%d", &entry[loop].age); fflush(stdin); /* flush the input stream in case of bad input */ /* input a salary as a float */ printf(" Salary : "); scanf("%f", &entry[loop].salary); fflush(stdin); /* flush the input stream in case of bad input */ } /* Input a name, age and salary as a string, integer, and double */ printf("/nPlease enter your name, age and salary/n"); scanf("%20s %d %lf", name, &age, &salary); /* Print out the data that was input */ printf("/n/nTable %s/n",label); printf("Compiled by %s age %d $%15.2lf/n", name, age, salary); printf("-----------------------------------------------------/n"); for (loop=0;loop<entries;++loop) printf("%4d | %-20s | %5d | %15.2lf/n", loop + 1, entry[loop].name, entry[loop].age, entry[loop].salary); printf("-----------------------------------------------------/n"); return 0; } 函数名: stpcpy 功 能: 拷贝一个字符串到另一个 用 法: char *stpcpy(char *destin, char *source); 程序例: #include <stdio.h> #include <string.h> int main(void) { char string[10]; char *str1 = "abcdefghi"; stpcpy(string, str1); printf("%s/n", string); return 0; } 函数名: strcat 功 能: 字符串拼接函数 用 法: char *strcat(char *destin, char *source); 程序例: #include <string.h> #include <stdio.h> int main(void) { char destination[25]; char *blank = " ", *c = "C++", *Borland = "Borland"; strcpy(destination, Borland); strcat(destination, blank); strcat(destination, c); printf("%s/n", destination); return 0; } 函数名: strchr 功 能: 在一个串中查找给定字符的第一个匹配之处/ 用 法: char *strchr(char *str, char c); 程序例: #include <string.h> #include <stdio.h> int main(void) { char string[15]; char *ptr, c = 'r'; strcpy(string, "This is a string"); ptr = strchr(string, c); if (ptr) printf("The character %c is at position: %d/n", c, ptr-string); else printf("The character was not found/n"); return 0; } 函数名: strcmp 功 能: 串比较 用 法: int strcmp(char *str1, char *str2); 程序例: #include <string.h> #include <stdio.h> int main(void) { char *buf1 = "aaa", *buf2 = "bbb", *buf3 = "ccc"; int ptr; ptr = strcmp(buf2, buf1); if (ptr > 0) printf("buffer 2 is greater than buffer 1/n"); else printf("buffer 2 is less than buffer 1/n"); ptr = strcmp(buf2, buf3); if (ptr > 0) printf("buffer 2 is greater than buffer 3/n"); else printf("buffer 2 is less than buffer 3/n"); return 0; } 函数名: strcpy 功 能: 串拷贝用 法: char *strcpy(char *str1, char *str2); 程序例: #include <stdio.h> #include <string.h> int main(void) { char string[10]; char *str1 = "abcdefghi"; strcpy(string, str1); printf("%s/n", string); return 0; } 函数名: strrev 功 能: 串倒转用 法: char *strrev(char *str); 程序例: #include <string.h> #include <stdio.h> int main(void) { char *forward = "string"; printf("Before strrev(): %s/n", forward); strrev(forward); printf("After strrev(): %s/n", forward); return 0; } 函数名: strset 功 能: 将一个串中的所有字符都设为指定字符 用 法: char *strset(char *str, char c); 程序例: #include <stdio.h> #include <string.h> int main(void) { char string[10] = "123456789"; char symbol = 'c'; printf("Before strset(): %s/n", string); strset(string, symbol); printf("After strset(): %s/n", string); return 0; } 函数名: strstr 功 能: 在串中查找指定字符串的第一次出现 用 法: char *strstr(char *str1, char *str2); 程序例: #include <stdio.h> #include <string.h> int main(void) { char *str1 = "Borland International", *str2 = "nation", *ptr; ptr = strstr(str1, str2); printf("The substring is: %s/n", ptr); return 0; } 函数名: strtod 功 能: 将字符串转换为double型值 用 法: double strtod(char *str, char **endptr); 程序例: #include <stdio.h> #include <stdlib.h> int main(void) { char input[80], *endptr; double value; printf("Enter a floating point number:"); gets(input); value = strtod(input, &endptr); printf("The string is %s the number is %lf/n", input, value); return 0; } 函数名: strtol 功 能: 将串转换为长整数 用 法: long strtol(char *str, char **endptr, int base); 程序例: #include <stdlib.h> #include <stdio.h> int main(void) { char *string = "87654321", *endptr; long lnumber; /* strtol converts string to long integer */ lnumber = strtol(string, &endptr, 10); printf("string = %s long = %ld/n", string, lnumber); return 0; } 函数名: strupr 功 能: 将串中的小写字母转换为大写字母 用 法: char *strupr(char *str); 程序例: #include <stdio.h> #include <string.h> int main(void) { char *string = "abcdefghijklmnopqrstuvwxyz", *ptr; /* converts string to upper case characters */ ptr = strupr(string); printf("%s/n", ptr); return 0; } 函数名: swab 功 能: 交换字节 用 法: void swab (char *from, char *to, int nbytes); 程序例: #include <stdlib.h> #include <stdio.h> #include <string.h> char source[15] = "rFna koBlrna d"; char target[15]; int main(void) { swab(source, target, strlen(source)); printf("This is target: %s/n", target); return 0; } 函数名: tolower 功 能: 把字符转换成小写字母 用 法: int tolower(int c); 程序例: #include <string.h> #include <stdio.h> #include <ctype.h> int main(void) { int length, i; char *string = "THIS IS A STRING"; length = strlen(string); for (i=0; i<length; i++) { string[i] = tolower(string[i]); } printf("%s/n",string); return 0; } 函数名: toupper 功 能: 把字符转换成大写字母 用 法: int toupper(int c); 程序例: #include <string.h> #include <stdio.h> #include <ctype.h> int main(void) { int length, i; char *string = "this is a string"; length = strlen(string); for (i=0; i<length; i++) { string[i] = toupper(string[i]); } printf("%s/n",string); return 0; }
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