String and for loop

Question

I wrote this C program to enter names and ages of 3 people. But the output wasn't my expectation. It was able to enter name and age for the first person, but it wasn't able for second and third persons. Please help.

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

int main()
{
    int i, age;
    char name[20];

    for(i=0; i<3; i++)
    {
        printf("\nEnter name: ");
        gets(name);

        printf("Enter age: ");
        scanf(" %d", &age);

        puts(name);
        printf(" %d", age);
    }

    return 0;
}

You should check the return value from `scanf()`. On your second loop, if you typed a name, that name would probably not be converted by `%d` and would be left in the input to be read the next time around the loop — while leaving you puzzled about what's going on. See [Why the `gets()` function is to dangerous to be used — ever!](https://stackoverflow.com/questions/1694036/) for why you should not use `gets()` and what alternatives are available. You should test that the replacement (which is likely to be `fgets()`) was successful. Always check input operations! — Jonathan Leffler, Oct 02 '18 at 05:44

score 1 · Answer 1 · answered Oct 02 '18 at 04:53

In short: Your 2nd puts is processing the '\n' from your scanf.

Fix by adding getchar(); after scanf

Explanation:

1st iteration:

    printf("\nEnter name: ");
    gets(name);                     // line is read from input
    printf("Enter age: ");
    scanf(" %d", &age);             // a number is read from input, and the newline char ('\n') remains in buffer
    puts(name);
    printf(" %d", age);

2nd iteration:

    printf("\nEnter name: ");
    gets(name);                     // previously buffered newline char is read, thus "skipping" user input
    printf("Enter age: ");
    scanf(" %d", &age);             
    puts(name);
    printf(" %d", age);

Same goes for 3rd iteration, and this is why you lose user input

It works now. Thank you – user10444184 Oct 02 '18 at 16:51 — user10444184, Oct 02 '18 at 16:51

VolAnd · Answer 2 · 2018-10-02T05:29:29.043

The best way to store information of more than one person is to use struct, like

  struct person {
      int age;
      char name[20];
  };

and make array of struct, like

 struct person people[3];

than use loop with accessing people[i].age and people[i].name, e.g.:

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

struct person {
    int age;
    char name[20];
};

#define ARR_SIZE 3

int main(int argc, char* argv[])
{
    struct person people[ARR_SIZE];
    int i;
    char *lastpos;
    for(i = 0; i < ARR_SIZE; i++)
    {
        printf("\nEnter name: ");
        scanf(" %s", people[i].name);
        if ((lastpos=strchr(people[i].name, '\n')) != NULL) *lastpos = '\0'; // remove newline from the end
        printf("Enter age: ");
        scanf(" %d", &people[i].age);
    }
    printf("This is the people you entered:\n");    
    for(i = 0; i < ARR_SIZE; i++)
    {
        printf("%d : %s : %d\n", i+1, people[i].name, people[i].age);
    }
    return 0;
}

UPDATE:

As you see I use scanf(" %s", people[i].name); instead of gets(people[i].name); to read name from stdin. Try both option for the following cases:

enter short name (e.g. John) and correct age (e.g. 15)
enter two word name (e.g. John Smith) and correct age (e.g. 17)
enter short name and uncorrect age (e.g. five)

Then read articles about value returned by scanf and cleaning input buffer

Thank you. I am a beginner to C language. But I will keep this for learning Struct later. — user10444184, Oct 02 '18 at 16:53
Good luck in C learning... keep putting one foot in front of the other — VolAnd, Oct 03 '18 at 10:48

String and for loop

2 Answers2