Thread: Validate positives

  1. #1
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    Sep 2017
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    Validate positives

    hi everyone i'm programming validation of a number that only accepts positive integers the code below is for only integers
    Code:
    • #include<ctype.h>
    • #include<stdio.h>
    • int main(void)
    • {
    • char buf[BUFSIZ];
    • int value, end;
    • printf("Enter an integer: ");
    • fflush(stdout);
    • while(fgets(buf,sizeof buf, stdin)== NULL ||
    • sscanf(buf,"%d%n",&value,&end)!=1||
    • !isspace(buf[end]))
    • {
    • printf("Invalid integer. Please try again: ");
    • fflush(stdout);
    • }
    • printf("You entered %d\n", value);
    • return0;
    • }
    But when i try to add it the validation of positives
    Code:
    
    
    • #include<ctype.h>
    • #include<stdio.h>
    • int main(void)
    • {
    • char buf[BUFSIZ];
    • int value, end;
    • printf("Enter an integer: ");
    • fflush(stdout);
    • while(value<0) { printf("Only positives numbers. Please try again: "); fflush(stdout); }
    • while(fgets(buf,sizeof buf, stdin)== NULL ||
    • sscanf(buf,"%d%n",&value,&end)!=1||
    • !isspace(buf[end]))
    • {
    • printf("Invalid integer. Please try again: ");
    • fflush(stdout);
    • }
    • printf("You entered %d\n", value);
    • return0;
    • }
    And when i compile ignores the validation of only positives. Help please.

  2. #2
    and the hat of int overfl Salem's Avatar
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    Because you didn't put your test in the same while condition as everything else.

    Try
    Code:
    while(fgets(buf,sizeof buf, stdin)== NULL ||
               sscanf(buf,"%d%n",&value,&end)!=1||
               !isspace(buf[end]) ||
               value < 0)
    Next time, make sure you post only code between code tags. No tables / formatting / fonts / colours.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  3. #3
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    i didn't put it because i want different messages, one message for only positives and another one for only integers

  4. #4
    and the hat of int overfl Salem's Avatar
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    So put the test inside the loop then
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

  5. #5
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    You mean put the (while<0) inside the other? i already do that, and the problem is when i enter a float number validates it then i enter a negative and doesn't validate it

  6. #6
    Hurry Slowly vart's Avatar
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    Quote Originally Posted by lifeless View Post
    You mean put the (while<0) inside the other? i already do that, and the problem is when i enter a float number validates it then i enter a negative and doesn't validate it
    No Salem means move your condition from while into loop body

    Code:
    while(fgets(buf,sizeof buf, stdin)== NULL ||
               sscanf(buf,"%d%n",&value,&end)!=1||
               !isspace(buf[end]))
        if(value < 0)
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

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