11. ポインタの応用と構造体

Source code

ポインタ引数で値を戻す

#include <stdio.h>
void func(int *dt);
int main(void)
{
    int nn;
    nn = 1234;
    printf("main: nn=%d\n", nn);
    func(&nn);
    printf("main: nn=%d\n", nn);
    return 0;
}
void func(int *dt)
{
    *dt = 5678;
    printf("func: *dt=%d\n", *dt);
}

ポインタで配列を関数に渡す

#include <stdio.h>
void func1(int d[], int len)
{
    int i;
    for (i = 0; i < len; i++)
        printf("%d ", d[i]);
    printf("\n");
}
void func2(int *d, int len)
{
    int i;
    for (i = 0; i < len; i++)
        printf("%d ", *(d + i));
    printf("\n");
}
int main(void)
{
    int nn[4] = {10, 20, 30, 40};
    func1(nn, 4);
    func2(nn, 4);
    return 0;
}

ポインタで文字列を関数に渡す

#include <stdio.h>
void strout_p(char *ss);
int main(void)
{
    char st[] = "ABCDEF";
    strout_p(st);
    return 0;
}
void strout_p(char *pp)
{
    printf("pp=%s\n", pp);
    while (*pp)
    { /* *pp!='\0'でも同じ */
        printf("%X ", *pp);
        ++pp;
    }
    printf("\n");
}

Problem

Problem 1. 下線部(4カ所)を埋めて，プログラムを完成させよ．

#include <stdio.h>
// void cmp(char ____, int *r)
{
    char *s2 = "microwave oven\n";
    // *r = ____;
    while (*s1 || *s2)
    {
        if (*s1 != *s2)
            return;
        // ____++;
        s2++;
    }
    *r = 0;
}
int main(void)
{
    char s[80];
    int result;
    fgets(s, 80, stdin);
    // cmp(s, ____);
    if (result == 1)
        printf("No\n");
    else
        printf("Yes\n");
    return 0;
}

Problem 2. 文字列を渡すと逆順にする関数reverse()を作れ．

#include <stdio.h>
#include <string.h> /*for strlen()*/
void reverse(char *s);
int main(void)
{
    
}
void reverse(char *s)
{
    int wk, n1 = 0, n2;
    n2 = strlen(s) - 1;
    while (n1 < n2)
    {
        wk = *(s + n1);
        *(s + n1) = *(s + n2);
        *(s + n2) = wk;
        ++n1;
        --n2;
    }
}

Problem 3. 文字列と繰り返す文字を，渡した文字数分，入力した文字列を繰り返し表示する関数を作れ．

#include <stdio.h>
void repeat(char *strp, int n);
int main(void)
{

}
void repeat(char *strp, int n)
{
    int i;
    char *p = strp;
    for (i = 0; i < n; i++)
    {
        if (*strp == '\0')
            strp = p;
        printf("%c", *(strp++));
    }
    printf("\n");
}

Problem 4. 下線部を埋めて，プログラムを完成させよ．

#include <string.h>
struct myst
{
    char name[40];
    int age;
};
int main(void)
{
    struct ____ Taro, Hanako;
    strcpy(______, "Tanaka Taro");
    ___ = 18;
    strcpy(______, "Yamada Hanako");
    ______ = 16;
    printf("%s is %d years old.\n", ______, ______);
    printf("%s is %d years old.\n", ______, ______);
    return 0;
}

Solutions

#include <stdio.h>
void cmp(char *s1, int *r)
{
    char *s2 = "microwave oven\n";
    *r = 1;
    while (*s1 || *s2)
    {
        if (*s1 != *s2)
            return;
        s1++;
        s2++;
    }
    *r = 0;
}
int main(void)
{
    char s[80];
    int result;
    fgets(s, 80, stdin);
    cmp(s, &result);
    if (result == 1)
        printf("No\n");
    else
        printf("Yes\n");
    return 0;
}

#include <stdio.h>
#include <string.h> /*for strlen()*/
void reverse(char *s);
int main(void)
{
    char str[] = "program";
    reverse(str);
    printf("str=%s\n", str);
    return 0;
}
void reverse(char *s)
{
    int wk, n1 = 0, n2;
    n2 = strlen(s) - 1;
    while (n1 < n2)
    {
        wk = *(s + n1);
        *(s + n1) = *(s + n2);
        *(s + n2) = wk;
        ++n1;
        --n2;
    }
}

#include <stdio.h>
void repeat(char *strp, int n);
int main(void)
{
    char str[100];
    printf("Input a string:");
    scanf("%s", str);
    repeat(str, 20);
    return 0;
}
void repeat(char *strp, int n)
{
    int i;
    char *p = strp;
    for (i = 0; i < n; i++)
    {
        if (*strp == '\0')
            strp = p;
        printf("%c", *(strp++));
    }
    printf("\n");
}

#include <stdio.h>
#include <string.h>
struct myst
{
    char name[40];
    int age;
};
int main(void)
{
    struct myst Taro, Hanako;
    strcpy(Taro.name, "Tanaka Taro");
    Taro.age = 18;
    strcpy(Hanako.name, "Yamada Hanako");
    Hanako.age = 16;
    printf("%s is %d years old.\n", Taro.name, Taro.age);
    printf("%s is %d years old.\n", Hanako.name, Hanako.age);
    return 0;
}