初心者がマスターするためのC言語atoi関数の使い方！10の詳細なステップ

#include <stdlib.h>
int main() {
    char str[] = "123";
    int num = atoi(str);
    printf("%d\n", num);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>

int main() {
    char str[] = "789";
    int num = atoi(str);

    printf("The number is %d\n", num);
    return 0;
}

#include <stdio.h>
#include <stdlib.h>

int main() {
    char str1[10], str2[10];

    printf("Enter two numbers: ");
    scanf("%s %s", str1, str2);

    int num1 = atoi(str1);
    int num2 = atoi(str2);

    printf("The sum is %d\n", num1 + num2);

    return 0;
}

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

int is_numeric(char* str) {
    for (int i = 0; str[i] != '\0'; i++) {
        if (!isdigit(str[i])) {
            return 0;
        }
    }
    return 1;
}

int main() {
    char str[] = "123abc";

    if (is_numeric(str)) {
        int num = atoi(str);
        printf("The number is %d\n", num);
    } else {
        printf("The string is not a number\n");
    }

    return 0;
}

#include <stdio.h>
#include <stdlib.h>

int main() {
    char str[10];

    printf("Enter a number: ");
    scanf("%s", str);

    int num = atoi(str);

    if (num >= 10) {
        printf("The number is greater than or equal to 10\n");
    } else {
        printf("The number is less than 10\n");
    }

    return 0;
}

#include <stdio.h>
#include <stdlib.h>

int main() {
    char str1[10], str2[10];

    printf("Enter two numbers: ");
    scanf("%s %s", str1, str2);

    int num1 = atoi(str1);
    int num2 = atoi(str2);

    printf("The sum is %d\n", num1 + num2);

    return 0;
}

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

int main() {
    char line[100];
    char *token;
    int sum = 0;

    FILE *file = fopen("data.csv", "r");
    if (file == NULL) {
        printf("Could not open file\n");
        return 1;
    }

    while (fgets(line, sizeof(line), file)) {
        token = strtok(line, ",");
        while (token != NULL) {
            sum += atoi(token);
            token = strtok(NULL, ",");
        }
    }

    fclose(file);

    printf("The sum of the numbers in the file is %d\n", sum);

    return 0;
}

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

int calculate(int num1, int num2, char* operator) {
    if (strcmp(operator, "+") == 0) {
        return num1 + num2;
    } else if (strcmp(operator, "-") == 0) {
        return num1 - num2;
    } else if (strcmp(operator, "*") == 0) {
        return num1 * num2;
    } else if (strcmp(operator, "/") == 0) {
        if (num2 != 0) {
            return num1 / num2;
        } else {
            printf("Error: Division by zero is not allowed\n");
            exit(1);
        }
    } else {
        printf("Error: Invalid operator\n");
        exit(1);
    }
}

int main() {
    char str_num1[10], str_num2[10], operator[2];

    printf("Enter two numbers and an operator: ");
    scanf("%s %s %s", str_num1, str_num2, operator);

    int num1 = atoi(str_num1);
    int num2 = atoi(str_num2);

    printf("The result is %d\n", calculate(num1, num2, operator));

    return 0;
}

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

int main() {
    char line[100];
    char *token;
    int sum = 0;
    int count = 0;

    FILE *file = fopen("large_data.csv", "r");
    if (file == NULL) {
        printf("Could not open file\n");
        return 1;
    }

    while (fgets(line, sizeof(line), file)) {
        token = strtok(line, ",");
        while (token != NULL) {
            sum += atoi(token);
            count++;
            token = strtok(NULL, ",");
        }
    }

    fclose(file);

    if (count > 0) {
        printf("The average of the numbers in the file is %f\n", (double)sum / count);
    } else {
        printf("The file does not contain any numbers\n");
    }

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

int main() {
    char str[10] = "123abc";
    char *endptr;

    errno = 0;  // errnoをリセット
    long num = strtol(str, &endptr, 10);

    if (endptr == str) {
        printf("No digits were found\n");
    } else if (errno == ERANGE) {
        printf("The number is out of the range of representable values\n");
    } else {
        printf("The number is %ld and its followed by %s\n", num, endptr);
    }

    return 0;
}

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

int main() {
    char input[100];
    char *token;
    int sum = 0;

    printf("Enter numbers separated by spaces: ");
    fgets(input, sizeof(input), stdin);

    token = strtok(input, " ");
    while (token != NULL) {
        sum += atoi(token);
        token = strtok(NULL, " ");
    }

    printf("The sum of the numbers is %d\n", sum);

    return 0;
}

#include <stdio.h>
#include <stdlib.h>
#include <errno.h>

int main() {
    char str[10] = "123abc";
    char *endptr;

    errno = 0;  // errnoをリセット
    long num = strtol(str, &endptr, 10);

    if (endptr == str) {
        printf("数値が見つかりませんでした\n");
    } else if (errno == ERANGE) {
        printf("数値が表現可能な範囲を超えています\n");
    } else {
        printf("数値は %ld で、その後に %s が続いています\n", num, endptr);
    }

    return 0;
}

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

int main() {
    char input[100];
    char *token;
    int sum = 0;

    printf("スペースで区切って数値を入力してください: ");
    fgets(input, sizeof(input), stdin);

    token = strtok(input, " ");
    while (token != NULL) {
        sum += atoi(token);
        token = strtok(NULL, " ");
    }

    printf("入力された数値の合計は %d です\n", sum);

    return 0;
}