String handling using library functions - Step-by-Step Execution

Concept Flow - String handling using library functions

Start

↓

Declare strings

↓

Call library function

↓

Function processes strings

↓

Return result

↓

Use result (print, compare, etc.)

↓

End

This flow shows how C string library functions take strings as input, process them, and return results used in the program.

Execution Sample

C

#include <stdio.h>
#include <string.h>

int main() {
  char str1[] = "Hello";
  char str2[] = "World";
  int result = strcmp(str1, str2);
  printf("Compare result: %d\n", result);
  return 0;
}

This code compares two strings using strcmp and prints the comparison result.

Execution Table

Step	Action	Input Values	Function Called	Function Result	Program Output
1	Declare str1	str1 = "Hello"	N/A	N/A	N/A
2	Declare str2	str2 = "World"	N/A	N/A	N/A
3	Call strcmp	str1 = "Hello", str2 = "World"	strcmp(str1, str2)	Negative value (e.g., -15)	N/A
4	Print result	result = -15	printf	N/A	Compare result: -15
5	Return from main	N/A	N/A	N/A	Program ends

💡 Program ends after printing the comparison result.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
str1	undefined	"Hello"	"Hello"	"Hello"	"Hello"
str2	undefined	undefined	"World"	"World"	"World"
result	undefined	undefined	undefined	Negative value (e.g., -15)	Negative value (e.g., -15)

Key Moments - 2 Insights

Why does strcmp return a negative number instead of just true or false?

strcmp returns a negative, zero, or positive number to show if the first string is less than, equal to, or greater than the second string. See step 3 in execution_table where result is a negative value meaning str1 < str2.

Why do we use char arrays for strings instead of just char variables?

Strings in C are arrays of characters ending with a special '\0' character. Each char variable holds one character only. See steps 1 and 2 where str1 and str2 are arrays holding multiple characters.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of 'result' after step 3?

A -15

B 0

C 15

D Undefined

💡 Hint

Check the 'Function Result' column in row for step 3.

At which step is the output 'Compare result: -15' printed?

A Step 2

B Step 4

C Step 3

D Step 5

💡 Hint

Look at the 'Program Output' column to find when the output appears.

If str1 was "World" and str2 was "Hello", what would strcmp likely return?

A A negative number

B Zero

C A positive number

D An error

💡 Hint

strcmp returns positive if first string is greater than second; see explanation in key_moments.

Concept Snapshot

C strings are char arrays ending with '\0'.
Use library functions like strcmp, strcpy, strlen.
strcmp compares strings and returns <0, 0, or >0.
strcpy copies one string to another.
strlen returns string length excluding '\0'.
Always include <string.h> to use these functions.

Full Transcript

This example shows how C handles strings using library functions. We declare two strings as char arrays: str1 with "Hello" and str2 with "World". Then we call strcmp to compare them. strcmp returns a negative number because "Hello" is less than "World" alphabetically. We store this result in the variable 'result'. Next, we print the result using printf, showing "Compare result: -15". Finally, the program ends. Key points: strcmp returns a number indicating order, not just true/false. Strings are arrays of chars ending with a null character. This trace helps visualize each step and variable change.