C言語のisdigit関数を理解する5つのステップ

#include <ctype.h>
int isdigit(int c);

#include <stdio.h>
#include <ctype.h>

int main() {
    char c1 = '5';
    char c2 = 'a';

    if(isdigit(c1)) {
        printf("%c is a digit.\n", c1);
    } else {
        printf("%c is not a digit.\n", c1);
    }

    if(isdigit(c2)) {
        printf("%c is a digit.\n", c2);
    } else {
        printf("%c is not a digit.\n", c2);
    }

    return 0;
}

5 is a digit.
a is not a digit.

#include <stdio.h>
#include <ctype.h>

int main() {
    char input;

    printf("Enter a character: ");
    scanf("%c", &input);

    if(isdigit(input)) {
        printf("You entered a digit.\n");
    } else {
        printf("You did not enter a digit.\n");
    }

    return 0;
}

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main() {
    char str[] = "Hello, 1234!";
    int count = 0;

    for(int i = 0; i < strlen(str); i++) {
        if(isdigit(str[i])) {
            count++;
        }
    }

    printf("Number of digits in the string: %d\n", count);

    return 0;
}

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main() {
    char password[50];
    int hasDigit = 0;

    printf("Enter your password: ");
    scanf("%s", password);

    for(int i = 0; i < strlen(password); i++) {
        if(isdigit(password[i])) {
            hasDigit = 1;
            break;
        }
    }

    if(hasDigit) {
        printf("Your password contains a digit.\n");
    } else {
        printf("Your password does not contain a digit.\n");
    }

    return 0;
}

#include <stdio.h>
#include <ctype.h>
#include <string.h>

int main() {
    char input[50];
    int isAllDigits = 1;

    printf("Enter a string: ");
    scanf("%s", input);

    for(int i = 0; i < strlen(input); i++) {
        if(!isdigit(input[i])) {
            isAllDigits = 0;
            break;
        }
    }

    if(isAllDigits) {
        printf("Your input contains only digits.\n");
    } else {
        printf("Your input contains characters other than digits.\n");
    }

    return 0;
}

#include <stdio.h>
#include <ctype.h>
#include <limits.h>

int main() {
    int input;

    printf("Enter a number: ");
    scanf("%d", &input);

    if(input >= CHAR_MIN && input <= CHAR_MAX) {
        if(isdigit(input)) {
            printf("It is a digit.\n");
        } else {
            printf("It is not a digit.\n");
        }
    } else {
        printf("The input is out of the valid range.\n");
    }

    return 0;
}