CODEWITHSUNDEEP
cfor-loopchar
Smith Will Suffice
Smith Will Suffice

Reputation: 99

How do you break out of a loop by a terminating character?

I am trying to write a simple demonstration program that will break out of a loop upon entering a designated character. I was able to do this successfully until I wanted to add the extra condition that I did not exceed my array. This code will not break out of the loop when I enter the designated character and I cannot figure out why. The logic and setup of the code seems sound! 

#include <stdio.h>

char input[10];
char breakout = '!';
int idx;

int main(void)
{
printf("Input characters until %c character is used to break out", breakout);

for(idx = 0; input[idx] != breakout && idx < 10; idx++)
{
    scanf("%c", &input[idx]);
}

printf("Program terminated:");

getchar();
return 0;   
}

It seems as though the condition of the for loop SHOULD evaluate false upon entering the '!' character, but it is not. Thanks guys

Upvotes: 0

Views: 1449

Answers (3)

Musa
Musa

Reputation: 97672

You are testing the condition before the character is entered, if you use a do-while loop you can make the comparison after

idx = 0;
do
{
    scanf("%c\n", &input[idx]);
}
while( input[idx++] != breakout && idx < 10);

Upvotes: 2

baifuyou
baifuyou

Reputation: 69

You should testing the condition after the character is inputted. I modified your code:

#include <stdio.h>
char input[10];
char breakout = '!';
int idx;

int main(void)
{
    printf("Input characters until %c character is used to break out", breakout);

    for(idx = 0; idx < 10; idx++)
    {
            scanf("%c", &input[idx]);
            if(input[idx] == '!')
              break;
    }
    printf("Program terminated:");

    getchar();
    return 0;
}

Upvotes: 1

struthersneil
struthersneil

Reputation: 2750

Think about your for loop conditions. Your input[idx] is always looking at the next location in the array (which does not yet contain a character)--not the previous character received from the scanf call, which would be found at input[idx - 1]. But of course you can't check input[idx - 1] on the first iteration, so watch out for that.

for(idx = 0; (idx == 0 || input[idx - 1] != breakout) && idx < 10; idx++) 
{    
  ... 
}

Super-complex for loop conditions are rarely a good idea for more or less this reason--that idx++ iteration step occurs before the evaluation of the condition and it can be confusing. Use a do/while or have a break condition in your loop.

Upvotes: 2

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