第四章 函数与程序结构

#include <stdio.h>
#define MAXLINE 1000
int add_getline(char line[], int max);
int strindex(char source[], char searchfor[]);

char pattern[] = "ray";

int main(void)
{
char line[MAXLINE];
int found = 0;

while(add_getline(line, MAXLINE) > 0){
printf("run here1\n");
if(strindex(line, pattern) >= 0){
printf("%s", line);
found++;
printf("run here2\n");
}
}
return found;
}

int add_getline(char s[], int lim)
{
int c, i;
i = 0;
while(--lim > 0 && (c=getchar()) != EOF && c != '\n') //EOF：ctrl+d,  '\n':enter
s[i++] = c;
if(c == '\n')
s[i++] = c;
s[i] = '\0';
printf("run here3 i:%d\n", i);
return i;
}

int strindex(char s[], char t[])
{
int i, j, k;
printf("run here4\n");
for(i = 0; s[i] != '\0'; i++){
printf("run here5\n");
for(j=i, k=0; t[k]!='\0' && s[j]==t[k]; j++, k++)
printf("s[%d]=%c, t[%d]=%c\n", j,s[j],k, t[k]);
if(k > 0 && t[k] == '\0'){
printf("k:%d\n",k);
return i;
}
}
printf("run here6\n");
return -1;
}
编译后执行，输入：hello world,显示：
hello world
run here3 i:12
run here1
run here4
run here5
run here5
run here5
run here5
run here5
run here5
run here5
run here5
run here5
s[8]=r, t[0]=r
run here5
run here5
run here5
run here6

输入：hello wrayorld，显示：
hello wrayorld
run here3 i:15
run here1
run here4
run here5
run here5
run here5
run here5
run here5
run here5
run here5
run here5
s[7]=r, t[0]=r
s[8]=a, t[1]=a
s[9]=y, t[2]=y
k:3
hello wrayorld
run here2

#include <ctype.h>
#include <stdio.h>
/* atof: convert string s to double */
double _atof(char s[])
{
double val, power;
int i, sign;
for (i = 0; isspace(s[i]); i++) /* skip white space */
;
sign = (s[i] == '-') ? -1 : 1;
printf("s[%d] = %d run here1\n", i, sign);
if (s[i] == '+' || s[i] == '-'){
i++;
printf("i=%d run here2\n", i);
}
for (val = 0.0; isdigit(s[i]); i++){
printf("i=%d\n", i);
val = 10.0 * val + (s[i] - '0');
printf("val = %lf run here4\n", val);
}
printf("i=%d\n", i);
if (s[i] == '.'){
printf("run here5\n");
i++;
}
if(isdigit(s[i]))
printf("Yes\n");
else
printf("No\n");
for (power = 1.0; isdigit(s[i]); i++) {
val = 10.0 * val + (s[i] - '0');
printf("run here6\n");
power *= 10;
}
printf("run here7\n");
return sign * val / power;
}
int main(void)
{
char s[100] = "-1234";
double res;
res = _atof(s);
printf("res value:%lf\n", res);
return 0;
}
编译后执行，显示：
s[0] = -1 run here1
i=1 run here2
i=1
val = 1.000000 run here4
i=2
val = 12.000000 run here4
i=3
val = 123.000000 run here4
i=4
val = 1234.000000 run here4
i=5
No
run here7
res value:-1234.000000

#include <stdio.h>
#define MAXLINE 100
/* rudimentary calculator */
int _getline(char s[], int lim)
{
int c, i;
i = 0;
printf("请输入数字：");
while(--lim > 0 && (c=getchar()) != EOF && c != '\n')
s[i++] = c;
if(c == '\n')
s[i++] = c;
s[i] = '\0';
return i;
}

main()
{
double sum, atof(char []);
char line[MAXLINE];
int _getline(char line[], int max);
sum = 0;
while (_getline(line, MAXLINE) > 0)
printf("相加后输出：%g\n", sum += atof(line));
return 0;
}
编译执行，显示：
请输入数字：1
相加后输出：1
请输入数字：2
相加后输出：3
请输入数字：10
相加后输出：13
请输入数字：a
相加后输出：13
请输入数字：=
相加后输出：13
请输入数字：7
相加后输出：20
请输入数字：

#include <stdio.h>
#include <stdlib.h> /* for atof() */
#include <ctype.h>
#include <ctype.h>
#define MAXVAL 100 /* maximum depth of val stack */
#define MAXOP 100 /* max size of operand or operator */
#define NUMBER '0' /* signal that a number was found */
#define BUFSIZE 100

int getop(char []);
void push(double);
double pop(void);
int getch(void);
void ungetch(int);

int sp = 0;
/* next free stack position */
double val[MAXVAL]; /* value stack */
char buf[BUFSIZE];
int bufp = 0;

/* reverse Polish calculator */
int main(void)
{
int type;
double op2;
char s[MAXOP];
printf("run here1\n");
while ((type = getop(s)) != EOF) {
switch (type) {
case NUMBER:
printf("run here2\n");
push(atof(s));
break;
case '+':
printf("run here3\n");
push(pop() + pop());
break;
case '*':
printf("run here4\n");
push(pop() * pop());
break;
case '-':
printf("run here5\n");
op2 = pop();
push(pop() - op2);
break;
case '/':
printf("run here6\n");
op2 = pop();
if (op2 != 0.0)
push(pop() / op2);
else
printf("error: zero divisor\n");
break;
case '\n':
printf("run here7\n");
printf("\t%.8g\n", pop());
break;
default:
printf("run here8\n");
printf("error: unknown command %s\n", s);
break;
}
}
return 0;
}

/* push: push f onto value stack */
void push(double f)
{
printf("run here9\n");
if (sp < MAXVAL)
val[sp++] = f;
else
printf("error: stack full, can't push %g\n", f);
}
/* pop: pop and return top value from stack */
double pop(void)
{
printf("run here10\n");
if (sp > 0)
return val[--sp];
else {
printf("error: stack empty\n");
return 0.0;
}
}

/* getop: get next character or numeric operand */
int getop(char s[])
{
printf("run here11\n");
int i, c;
while ((s[0] = c = getch()) == ' ' || c == '\t')
printf("run here11-1\n");
s[1] = '\0';
printf("run here11-2\n");
if (!isdigit(c) && c != '.'){
printf("run here11-3\n");
return c;    /* not a number */
}
i = 0;
if (isdigit(c)){
printf("run here11-4\n");
while (isdigit(s[++i] = c = getch()))
;
}
if(c == '.'){
printf("run here11-5\n");
while(isdigit(s[++i] = c = getch()))
;
}
s[i] = '\0';
if (c != EOF)
ungetch(c);
printf("run here11-6\n");
return NUMBER;
}

int getch(void)
{
printf("run here12\n");
return (bufp > 0) ? buf[--bufp] : getchar();
}

void ungetch(int c)
{
printf("run here13\n");
if (bufp >= BUFSIZE)
printf("ungetch: too many characters\n");
else
buf[bufp++] = c;
}
编译执行，显示：
run here1
run here11
run here12
3 7 +
run here11-2
run here11-4
run here12
run here13
run here11-6
run here2
run here9
run here11
run here12
run here11-1
run here12
run here11-2
run here11-4
run here12
run here13
run here11-6
run here2
run here9
run here11
run here12
run here11-1
run here12
run here11-2
run here11-3
run here3
run here10
run here10
run here9
run here11
run here12
run here11-2
run here11-3
run here7
run here10
10
run here11
run here12

#include <stdio.h>
/* printd: print n in decimal */
void printd(int n)
{
if (n < 0) {
putchar('-');
n = -n;
}
printf("debug1\n");
if (n / 10){
printf("debug2\n");
printd(n / 10);
}
printf("debug3\n");
putchar(n % 10 + '0');
printf("debug4\n");
printf("\n");
}

int main()
{
printd(123);
}
显示：
debug1
debug2
debug1
debug2
debug1
debug3
1debug4

debug3
2debug4

debug3
3debug4