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Today’s Material

This article explores the concept of variable scope in C programming, detailing how variables can be accessed within specific code blocks. It emphasizes the importance of temporary variables and illustrates their behavior within loops, explaining how they are created, used, and discarded. Examples demonstrate occlusion and overlapping scopes with variables having the same name, highlighting best practices for variable management to avoid confusion. Whether you're a beginner or an experienced programmer, understanding these concepts will improve your coding skills.

hilel-ramsey
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Today’s Material

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  1. Today’s Material • scope of variables • temporary variables • compound statements (blocks) and variables

  2. printed in the for loop scope of n printed at the end Scope of a Variable • "Scope of a variable" is the section of code where the variable can be accessed • That is, its value can be read/modified. int main(){ int n; for(n = 0; n < 5; n++) { printf("%d + ", n); } printf("%d = %d\n", n, n * (n + 1) / 2); return 0; } 0 + 1 + 2 + 3 + 4 + 5 = 15

  3. Scope of sum Scope of n Scope of a Variable • We can define new variables at the beginning of ANYcode block • In portions of the code enclosed within '{' and '}‘ • Scope of those variables will only be the code block in which they are declared + 0 = 0 + 1 = 1 + 2 = 3 + 3 = 6 + 4 = 10 int main(){ int n; for(n = 0; n < 5; n++) { int sum = n * (n + 1) / 2; printf(" + %d = %d\n", n, sum); } return 0; }

  4. Temporary Variables • In the previous program, sum is a temporary variable. • The for loop executes five times, for n = 0, 1, 2, 3, and 4. • Each time, a new sum variable is created, used to hold the value of a formula, printed on the screen, and thrown away at the end.

  5. Scope of x2 Scope of x6 Scope of x Temporary Variable Examples • This sample code uses a compound statement just to be able to create temporary variables: int main(){ double x = 0.12; printf("x = %.6lf\n", x); { double x2 = x * x; double x6 = x2 * x2 * x2; printf("x^2 = %.6lf\n", x2); printf("x^6 = %.6lf\n", x6); } return 0; } x = 0.120000 x^2 = 0.014400 x^6 = 0.000003

  6. Overlapping Scopes; Occlusion • Two variables by the same name can be used, but this is not a good idea. • The more local/temporary variable will occlude the other variable. • Only the local variable will be accessible. • The other variable can't be reached.

  7. Scope of first n Scope of temporary n Occluded Variable Example int main() { int n = 573; printf("n = %d\n", n); { int n = -1234; printf("n = %d\n", n); } printf("n = %d\n", n); return 0; } • These are two different variables • We can't access the first n • within the compound statement n = 573 n = -1234 n = 573

  8. Multiple Scopes and Occluded Variable Example int main() { double n = 1.99; printf("n = %.4lf\n", n); { int n = 573; printf("n = %d\n", n); } { int n = -1234; printf("n = %d\n", n); } printf("n = %.4lf\n", n); return 0; } There are three different variables n = 1.9900 n = 573 n = -1234 n = 1.9900

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