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Matt Bishop Office: 2209 Watershed Sciences Phone: +1 (530) 752-8060 Email: mabishop@ucdavis.edu |
Version of April 2, 2024 at 12:13PM
/*
* SCANF -- shows how to read using a format
*
* Usage: scanf (or ./scanf)
*
* Inputs: You are prompted for these
* Outputs: various formatted values
* Exit Code: 0 because all goes well
*
* IMPORTANT NOTE:
* When you compile this with gcc and -Wall, you get
* warnings about bad printfs; those are there for
* demonstration
*
* written for ECS 36A, Fall 2019
* modified for ECS 36A, Spring 2025 to fix incompatibilities with earlier version
*
* Matt Bishop, Oct. 11, 2019
* original program written
* Matt Bishop, Apr. 6m,2025
* modified for C11 to fix incompatibilities with earlier version of C
*/
#include <stdio.h>
int main(void)
{
int i, j; /* variables for input */
int r; /* return value of scanf */
int k; /* used to break out of a while loop */
int c; /* used to read a line */
char x; /* variable for input */
/*
* read in an integer
*/
printf("enter an integer: ");
if ((r = scanf("%d", &i)) == 1)
printf("You typed '%d'\n", i);
else if (r == EOF){
printf("You typed EOF to end input\n");
return(0);
}
else
printf("You didn't type an integer\n");
/*
* now read 2 integers
*/
printf("enter 2 integers: ");
if ((r = scanf("%d %d", &i, &j)) == 2)
printf("You typed '%d %d'\n", i, j);
else if (r == 1)
printf("You typed '%d' and a non-integer\n", i);
else if (r == EOF){
printf("You typed EOF to end input\n");
return(0);
}
else
printf("You didn't type an integer\n");
/*
* here's a good way to mess up
*/
printf("enter a string that doesn't begin with a number: ");
k = 100;
while (k > 0 && scanf("%d %d", &i, &j) != 2){
if (k % 10 == 0)
printf("Going around for the %d-th time\n", k);
k = k - 1;
}
printf("What happened is it tries to read another. But it sees a non-digit\n");
printf("Bnd so does not read it, and returns -1. But it then goes back (the\n");
printf("while loop) and repeats this. Were it not for the k this would go\n");
printf("on indefinitely. So *always* check that the return value of scanf is\n");
printf("EOF or what you expect.\n");
/*
* Here's an idiom to clean out the unread part of the line
*/
while ((c = getchar()) != '\n' && c != EOF)
printf("read char '%c'\n", c);
/*
* now we can read an integer
*/
printf("enter an integer: ");
if ((r = scanf("%d", &i)) == 1)
printf("You typed '%d'\n", i);
else if (r == EOF){
printf("You typed EOF to end input\n");
return(0);
}
/*
* now we read a character
*/
printf("Now we read the character following the integer you typed above\n");
printf("If we didn't type anything else, just hit return or enter, it\n");
printf("that's what is read and printed; if it's any other character,\n");
printf("the rest of the line is discarded; if you typed EOF, then every\n");
printf("future scanf in the program returns EOF.\n");
if ((r = scanf("%c", &x)) == 1)
printf("You typed '%c'\n", x);
else if (r == EOF){
printf("You typed EOF to end input\n");
return(0);
}
else
printf("You didn't type an integer\n");
return(0);
}
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ECS 36A, Programming & Problem Solving Version of April 2, 2024 at 12:13PM
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You can get the raw source code here.
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