I have just started learning loops in c programming, and have attempted to create a simple program to test my knowledge but it will not work

Question

I simply want a program that has the user input a value for a and b, and will ask the user to repeat this process if the value a is less than b. Here is my program:

#include <stdio.h>
#include <math.h>
int main(void)
{
        int a, b ,c;

while (a<=b)
{
        printf("Please enter a value for a:\n");
        scanf("%d", &a);
        printf("Please enter a value for b:\n");
        scanf("%d", &b);

        if (a<=b)
                printf("a must be greater than b:\n");
}
        c=a+b;
        printf("The answer of c is: %d\n", c);
return 0;
}

As soon as i run the program, it prints: "The answer of c is: 1829030" (Please note that the last number is always random)

Please help me run this program.

score 0 · Answer 1 · answered Apr 27 '17 at 10:17

The value of an uninitialized non static local variable is indeterminate. This means that the value can be anything at run time. In this case, the values of a, b, c are random and the loop may or may not be entered based on the random values of a, b, c.

try -

int a = 0, b = 0, c;

score 0 · Answer 2 · edited May 23 '17 at 12:02

0

You declare variables a, b, c but you do not give them an initial value. That means that they have an indeterminate value. Right after declaring a and b with no value given, you go on and compare them in your while (a <= b) condition. C does not know how to compare these value-less variables apparently, so it skips your loop altogether. You could avoid this problem by giving int a = 0, b = 1 values initially. This way you make sure that the loop will at least run once.

What happens with uninitialized variables is explained in this other SO answer

edited May 23 '17 at 12:02

Community

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answered Apr 27 '17 at 10:17

Freeman Lambda

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thank you! However i have used programs without declaring a and b with values and the program worked. Could you please explain when you are supposed to declare these with values? – L.Kay Apr 27 '17 at 10:21
Please read this other answer on SO: http://stackoverflow.com/questions/4532871/define-integer-int-whats-the-default-value – Freeman Lambda Apr 27 '17 at 10:25

I have just started learning loops in c programming, and have attempted to create a simple program to test my knowledge but it will not work

2 Answers2