makefile
.SUFFIXES: .c .o CC=gcc SRCS=test.c OBJS=$(SRCS:.c=.o) EXEC=test all: $(OBJS) $(CC) -o $(EXEC) $(OBJS) @echo '-------------ok--------------' .c.o: $(CC) -Wall -g -o $@ -c $< clean: rm -f $(OBJS) rm -f core*
myitoa
#include <stdio.h>
#include <string.h>
void resver(char *s)//反转字符串
{
int len = strlen(s);
//printf("len=%d\n",len);
int i = 0;
char tmp = 0;
for (; i<len/2; i++)
{
tmp = s[i];
s[i] = s[len-1-i];
s[len-1-i] = tmp;
}
}
const char *myitoa(int n)
{
static char buf[100];//必须为static,或者是全局变量
memset(buf, 0, sizeof(buf));
int FlagF = 0; //1-f, 0-z
int i = 0;
if (n < 0)
{
FlagF = 1;
n = 0 - n;
}
while (n)
{
buf[i++] = n % 10 + '0';
n = n / 10;
}
if (FlagF == 1)
{
buf[i++] = '-';
}
buf[i] = '\0';
printf("before buf:%s\n", buf);
resver(buf);
printf("after buf:%s\n", buf);
return buf;
}
int main()
{
printf("%s\n", myitoa(123));
printf("%s\n", myitoa(-123));
return 0;
}
myatoi
#include <stdio.h>
int mystrlen(const char *s)
{
int i = 0;
while (*s++)
{
i++;
}
return i;
}
int power10(int n)
{
if (n == 0)
{
return 1;
}
int val = 1;
int i = 0;
for (; i < n; i++)
{
val = val * 10;
}
return val;
}
int char2i(char c)
{
if ((c >= '0') || (c <= '9'))
{
return (c - '0');
} else
{
return 0;
}
}
int myatoi(const char *str)
{
int FlagF = 0; //1-f, 0-z
const char *p = str;
int i = 0;
int value = 0;
if (str[0] == '-')
{
FlagF = 1; //
p = ++str;
}
int len = mystrlen(p);
int lentmp = len;
for (; i < len; i++)
{
value += char2i(p[i]) * power10(lentmp - 1);
lentmp--;
}
if (FlagF == 1)
{
return (0 - value);
} else
{
return value;
}
}
int main()
{
const char *s = "-123";
printf("%d\n", myatoi(s));
return 0;
}
