C: Loop only prints the last index - arrays

Question

I am new to C, so excuse me for asking a seemingly easy question. but I have a loop which loops depending on the user, and inside the loops it asks for a name and an age, however when I go to print, it only prints the last entry and not all the entries I want.
#include <stdio.h>
int main()
{
int size,age;
char name [30];
printf("How long to loop for: ");
scanf("%d", &size);
for (int i=0; i<size; i++)
{
printf("Enter first name: ");
scanf("%s", name);
printf("Enter %s's age: ",name);
scanf("%d",&age);
printf("name: %s, age: %d\n", name,age);
}
return 0;
}

Answer 1

Right now your name and age variables will only hold the last input they received, thats why you're program only prints the last index. You need an array of int as well as an array of char [] to "hold" each input they receive, otherwise those inputs get lost and you only get input for the last index.
your variables should be initialized like:
int size;
printf("Enter size: ");
scanf("%d", &size);
int age [size];
char name[size][30];
in order to get user input and print each entry you will need to access each index by looping through the array size.
to access each index:
age[i]
name[i]
Please Note: using scanf to get a string from user input is generally bad, as it can cause problems if you happen to use a space(such as inputting your full name for example) in your input, and it can cause a buffer overflow if your string is longer than the buffer. Instead you can use fgets, but for your question it isn't necessary, just something to considered in the future in case you want to have spaces in your inputs.

Answer 2

Are you sure that the first scanf actually reads a number.
You want the following to check
if (scanf(" %d", &size) != 1) { // Note space - Eats white space/new lines
printf("Error - invalid size\nExiting\n");
return -1;
}
Prevent buffer overruns
Use:
scanf(" %29s", name); // See above
See point 1 for age
I think this will solve your problems

Answer 3

Okay so if I am understanding you correctly, you are looping through the for loop size number of times and each time you are setting the contents of the variables age and name. It sounds like you are expecting each iteration through the loop to save your entered instance of age and name but this is not the case.
Since you only have one age and one name variable they are going to store whatever the most recently taken input was. So this means whatever was entered on the last loop is what was last written into the variables name and age.
If you then try to print the contents of those variables you are going to see whatever was most recently entered into those variables. you would need more than one name and more than one age variable to write into if you were trying to save multiple entries.
Okay so Anthony, maybe you need to try a little bit of review when it comes to allocating memory. So when we declare the variable
int age;
we are telling the compiler to allocate enough memory to store one single integer that we will call 'age' in our program. since we only asked for enough memory to store one integer, every time you scanf() into the age variable, the single integer is written into that space.
What you want is to store a new integer every time you do another run through your for loop. So, you could declare an array of integers as follows.
int age[20];
Now we have asked the compiler to allocate enough space to store 20 different integers. there will an integer in position age[0] and another integer in age[1] and another in age[2] so on. So now you could use a loop to index through your array and store each entered age from stdin into a different position in the array as follows
for(int i=0; i<20; i++)
{
printf("Please enter your age: ");
scanf("%i", &age[i]);
}
So this loop starts with i=0 and so enters the input from stdin to age[0], the next iteration through the loop has i=1 and so enters the stdin input to age[1] and so on.
Hopefully this clarifies things a bit more?

Answer 4

A major fault is that your printfs will not be displayed as they are buffered.
You need a fflush after them
i.e.
printf("How long to loop for: ");
fflush(stdout);
And
printf("Enter first name: ");
fflush(stdout);
etc...